JPH0983079A - Semiconductor element - Google Patents

Abstract

(57) Abstract: A semiconductor device having a low operating voltage is provided. An n-type GaAs semiconductor substrate (11) and a buffer layer (1) formed on the semiconductor substrate (11).
2). The buffer layer (12) is 1 × 10 ⁸ cm ^-2
It has the above defect density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device such as a semiconductor light emitting device and a semiconductor laser device which can operate at a low operating voltage.

[0002]

2. Description of the Related Art In recent years, in order to improve the recording density of optical discs and the resolution of laser printers, there is an increasing demand for semiconductor lasers capable of emitting light with a short wavelength.
Active research is being conducted to realize this.

As an example thereof, Electronics Letters, Vol. 29, No. 16,
1488-1489, n-type Ga on an n-type GaAs substrate
As buffer layer, n-type ZnSe buffer layer, n-type ZnS
Se layer, n-type ZnMgSeS cladding layer, n-type ZnSS
e light guide layer, ZnCdSe / ZnSSe multiple quantum well active layer, p-type ZnSSe light guide layer, p-type ZnMgSe
S cladding layer, p-type ZnSSe layer, p-type ZnSe layer, p
-Type ZnSe / ZnTe superlattice layer and p-type ZnTe contact layer are sequentially stacked, and Pd / is formed on the p-type ZnTe contact layer.
A semiconductor laser device in which a p electrode made of pt / Au and an n electrode made of In are formed on a GaAs substrate is described. It is reported that this semiconductor laser device emits blue-green light and can perform continuous oscillation at room temperature.

However, the above semiconductor laser device is
Continuous operation and high reliability at a temperature higher than room temperature required for a practical semiconductor laser have not been obtained. This is much higher than the voltage (about 2.5 V) corresponding to the oscillation wavelength expected as the operating voltage (10 to 20 V).
V) has to be applied, and as a result, ineffective heat is generated, and as a result, the element temperature rises higher than the ambient temperature.

The cause of such a rise in element temperature is
It has been reported so far that it is difficult to form an electrode capable of making ohmic contact with a p-type wide gap II-VI group compound semiconductor and that an excessive voltage drop occurs at the interface with the electrode. Measures have been taken against.

[0006]

However, even if the above problem is solved, a sufficient reduction of the operating voltage cannot be achieved. Therefore, an object of the present invention is to provide a semiconductor device that can be driven at a low operating voltage.

[0007]

The present invention firstly includes a semiconductor substrate and a semiconductor layer formed on the semiconductor substrate, the semiconductor layer being at least partially 1 × 10 ⁸ c.
Provided is a semiconductor device having a defect density of m ^-2 or more.

Secondly, the present invention comprises a semiconductor substrate and a semiconductor layer formed on the semiconductor substrate, wherein the semiconductor layer has a defect density of at least 1 × 10 ⁴ cm ^-2 or less. A semiconductor device characterized by the above.

Thirdly, the present invention comprises a semiconductor substrate and a semiconductor layer formed on the semiconductor substrate, wherein the semiconductor layer has a portion having a defect density of 1 × 10 ⁸ cm ^-2 or more.
A semiconductor element including a portion having a defect density of × 10 ⁴ cm ^-2 or less.

Fourthly, the present invention has a semiconductor substrate and a semiconductor layer formed on the semiconductor substrate, and a bond radius of a covalent bond between mother elements constituting the semiconductor layer constitutes the substrate. When the bond radius is larger than the bond radius of the covalent bond between the mother elements, the impurity having an atomic radius smaller than the bond radius or the bond radius of the covalent bond between the mother elements forming the semiconductor layer constitutes the substrate. When the semiconductor element has a bond radius smaller than the bond radius of the covalent bond between the mother elements, the semiconductor layer is doped with an impurity having an atomic radius larger than the bond radius.

When forming a semiconductor layer forming a II-VI group compound or other hetero interface on a semiconductor substrate, the present inventors at least partially form the semiconductor layer depending on the constituent material of the semiconductor layer, the crystal structure, and the like. By introducing a region having a defect density of 1 × 10 ⁸ cm ⁻² or more or at least a region having a defect density of 1 × 10 ⁴ cm ⁻² or less, the resistance value of the portion can be reduced. , And found that the operating voltage of the device can be significantly reduced.

That is, for example, when a ZnSe-based compound semiconductor layer is grown on a III-V group compound semiconductor substrate such as GaAs, the interface (hetero interface) between the substrate and the grown semiconductor layer is usually in the order of 10 ⁴ cm ^-2. To 10 ⁸ cm ^-2 , crystal defects with a density in the first half of the 10 'cm ² range occur. The occurrence of crystal defects is caused by lattice mismatch, the surface state of the substrate, the growth mode of semiconductor layer crystals, and the like. It is said that crystal defects such as dislocations generated at the hetero interface propagate to the active layer, or propagate dislocations multiply when the operating voltage is high to deteriorate the active layer and shorten the life of the laser. The crystal defect density generated at the hetero interface depends on (1) the selection of the growth substrate and the material to be deposited and grown on it, (2) the control of the surface state of the substrate and the buffer layer at the initial stage of growth, and (3) the control of the growth mode. Change. Conventionally, a method of reducing the density of crystal defects itself has been used in order to suppress the propagation of dislocations to the active layer as much as possible. For example, a GaAs substrate and Zn grown on it
In order to prevent the generation of dislocations at the interface with the semiconductor layer made of Se-based material, the surface of the GaAs substrate is As controlled by temperature control.
Method to control the three-dimensional growth by forming the GaAs surface,
A method of growing an nSe-based material has been adopted. By reducing the density of crystal defects such as dislocations introduced between the substrate and the growth layer in this way, deterioration of the active layer is suppressed. However, contrary to this, the present inventor has clarified that the operating voltage of the device increases as the crystal defect density decreases.

As a result of further diligent research conducted by the present inventors, in the first aspect of the present invention, for example, III--
When a ZnSe-based II-VI group compound semiconductor layer is formed on a Group V compound semiconductor substrate, a region having a crystal defect density of 10 ⁸ cm ⁻² or more is introduced into at least a part of the semiconductor layer to form a device. It was found that the operating voltage can be significantly reduced, and the present invention has been completed. As a method of introducing such a high density defect region, (1)
A method of forming a Ga surface on the substrate surface to promote three-dimensional growth in the initial stage of growth, (2) a method of using a substrate having many crystal defects, (3) a lattice mismatch between the substrate and the growth layer. A method of interposing a buffer layer made of a II-VI group or a III-V group compound for increasing matching, (4) a method of increasing the thickness of the buffer layer directly above the substrate to a critical film thickness or more are conceivable. These methods only introduce defect densities in the low 10 ⁸ cm ⁻² range. The most convenient method for forming a high density crystal defect region is to form a G on the substrate surface.
This is a method of growing a semiconductor layer after forming an a-plane and irradiating an area where a high-density crystal defect area is to be formed with an electron beam. A desired high density defect region is formed on the electron irradiation site.

According to the first aspect of the present invention, by introducing a region having a crystal defect density of 10 ⁸ cm ^-2 or more,
ZnSe, ZnMgSSe, ZnTe, CdZnS are semiconductors that can reduce the operating voltage of the device.
There are II-VI group compound semiconductors such as e and ZnMgCdSe.

By the way, depending on the kind of semiconductor material grown on the semiconductor substrate, the crystal defect density is 1 × 10 ⁴ c.
It has been found that the operating voltage of the device can be reduced by setting m ⁻² or less. In such a semiconductor material, when the crystal defect density is 1 × 10 ⁸ cm ⁻² or more, the operating voltage of the device becomes high. That is, the present invention provides, in a second aspect, a semiconductor layer grown on a substrate at least partially
A region having a crystal defect density of × 10 ⁴ cm ^-2 or less is formed.

Whether the high-density crystal defect region or the low-density crystal defect region has a high operating voltage (current hardly flows at the interface) or a low operating voltage (current easily flows at the interface) is a semiconductor. It was found that it depends on the type, crystal structure, and combination with the substrate. For example, as a combination in which a current easily flows in the interface in the high-density crystal defect region and a current hardly flows in the low-density crystal defect region in the interface, ZnSe / GaA
s substrate, ZnSe / GaAlAs buffer layer / GaAs
Substrate, ZnSe / InGaAs buffer layer / GaAs substrate, ZnSe / ZnSe substrate, GaN / SiC substrate and the like. On the other hand, as a combination in which a current does not easily flow in the interface in the high-density crystal defect region and a current easily flows in the interface in the low-density crystal defect region, a ZnSe / Si substrate, a ZnSe / InP substrate, and a ZeSe / InGaAlP substrate are available.
Buffer layer / GaAs substrate, GaN / GaAs substrate, G
An aN / Si substrate or the like.

As described above, the combination of the semiconductor type, the crystal structure, and the substrate determines which of the high-density crystal defect region and the low-density crystal defect region has the lower resistance, which is obtained by a simple experiment. be able to. For example, FIG. 3 shows the operating voltage of the laser when the density of defects introduced into the n-type ZnSe buffer layer 12 is variously changed in the semiconductor structure according to the first embodiment described in detail below.
In this case, as apparent from FIG. 3, the defect density is 1 ×.
If it exceeds 10 ⁸ cm ^-2 , the operating voltage drops sharply.

On the contrary, for example, an n-type ZnSe layer (thickness 10 nm), a CdZnSe quantum well active layer, a p-type ZnSSe (thickness 2 μm), a p-type on an n-type GaAs substrate via an InGaAlP buffer layer. ZnSe layer (thickness 10
0 nm) and a p-type ZnSe / ZnTe superlattice contact layer are sequentially stacked, and a semiconductor sample is cleaved into a 400 μm square,
N-type Z when a predetermined electrode is formed and a current is applied
FIG. 4 shows the relationship between the defect density of the nSe layer and the voltage at a current value of 1 KA / cm ² . In this case, as can be seen from FIG. 4, the defect density in the n-type ZnSe layer is 10 ⁴ cm.
^In the case of ⁻² or less, the voltage shows a low value of 3 V or less, whereas in the case of the defect density exceeding 10 ⁴ cm ⁻² , the voltage sharply rises. After that, the voltage gradually increases with the increase of the defect density, but when the defect density becomes higher than that, the voltage further rapidly increases to reach 30V or higher. As described above, even when the same GaAs substrate is used for growing a ZnSe-based semiconductor thin film, the inventors of the present invention depend on whether the As-based semiconductor material or the P-based semiconductor material is used as the buffer layer, depending on the crystal defect density at the interface. It was found that the relationship between and the ease of current flow is reversed.

By forming such a high-density crystal defect region and a low-density crystal defect region in the same semiconductor layer, a difference occurs in the ease with which an applied current flows in the semiconductor layer, so that a current confinement structure is formed. It turns out that we can offer. The invention, in a third aspect, provides such a semiconductor structure.

By the way, although the high-density crystal defect region or the low-density defect region can be provided in the same semiconductor layer according to the kind of semiconductor material, the crystal structure, etc. as described above, the operating voltage of the device can be lowered. If the semiconductor layer to be formed can be heavily doped, the operating voltage of the device can also be reduced by this.

For example, on an n-type GaAs substrate, n-type Ga
As buffer layer, n-type ZnSe layer, n-type ZnSSe layer,
Undoped ZnSSe layer, p-type ZnSSe layer and p-type Z
Regarding a semiconductor structure formed by sequentially stacking nSe layers, an n-type Z
Both the nSe layer and the n-type ZnSSe layer are C
When the p-type ZnSSe layer and the p-type ZnSe layer were both doped with nitrogen according to the prior art, the effective donor concentration of each layer and the acceptor layer were examined by capacitance-voltage measurement. As a result, as shown in FIG.
As designed in the ZeSe layer (5 × 10 ¹⁸ cm for Cl)
It was found that high-concentration doping of 5 × 10 ¹⁸ cm ⁻³ ) was achieved with ⁻³ and N, but high-concentration doping was not achieved with the ZnSSe layer.

As a result of diligent studies by the present inventors in order to solve this, when the bond radii of covalent bonds between the mother elements constituting the substrate and the semiconductor layer formed thereon are different from each other, that is, In order to achieve high-concentration doping (that is, to form a low-resistance semiconductor layer), when the lattice mismatch exists between the substrate and the semiconductor layer formed on the substrate, the lattice mismatch is reduced. It has been found that it is necessary to select the dopant in the direction. That is, in the fourth aspect of the present invention, when the bond radius of the covalent bond between the mother elements forming the semiconductor layer formed on the substrate is larger than the bond radius of the covalent bond between the mother elements forming the substrate. Is an impurity having an atomic radius smaller than the bond radius, when the bond radius of the covalent bond between the mother elements forming the semiconductor layer is smaller than the bond radius of the covalent bond between the mother elements forming the substrate, The semiconductor layer is doped with an impurity having an atomic radius larger than the bond radius.

By the way, according to the fourth aspect of the present invention, an element having the same structure as that shown in FIG. 7A was manufactured, and iodine (I) was used instead of Cl in the n-type ZnSSe layer, and p-type Z.
When the nSSe layers were doped with arsenic (As) instead of N, the ZnSSe layers were also highly doped as shown in FIG. 7 (b).

The above results show that GaA is obtained for each dopant.
s substrate and the degree and the effective donor concentration of lattice mismatch (N _D), FIG. 8 in relation to the effective acceptor concentration (N _A)
Shown in FIG. 8A shows the case where Cl (conventional example) or I (the present invention) is used as the dopant, and FIG.
The case where N (conventional example) or As (present invention) is used as a dopant is shown.

[0025]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a sectional view showing the outline of a semiconductor device (semiconductor laser) according to the first embodiment. As shown in FIG. 1, a Cl-doped n-type ZnSe buffer layer 12 having a crystal defect density of about 1 × 10 ⁹ cm ⁻² is formed on the n-type GaAs substrate 11. The buffer layer 12 is formed by irradiating the entire surface of the substrate 11 with an electron beam and growing Cl-doped n-type ZnSe on it. On the n-type ZnSe buffer layer 12,
Cl-doped n-type ZnSSe layer 13 and Cl-doped n-type Z
The nMgSSe layer 14 is formed. Furthermore, n-type Z
On the nMgSSe layer 14, 10 layers each of an n-type ZnMgSSe layer having a thickness of 5 nm and a strain of + 1% and an n-type ZnSSe layer having a thickness of 5 nm and having a strain of -1% are stacked in layers of 10 layers each (multi-superlattice structure (crystal defect propagation)). A stop layer) 15 is formed. A Cl-doped n-type ZnSSe optical guide layer 16 and ZnCdSe / ZnS are formed on the crystal defect propagation stopping layer 15.
Se multiple quantum well active layer 17, N-doped p-type ZnSSe
Optical guide layer 18, N-doped p-type ZnMgSeS cladding layer 19, N-doped p-type ZnSSe layer 20, N-doped p-type ZnSe layer 21, p-type ZnSe / ZnTe superlattice layer 22.
And an N-doped p-type ZnTe contact layer 23 are sequentially stacked. p-type ZnSe layer 21, p-type ZnSe / Zn
The laminated structure including the Te superlattice layer 22 and the p-type ZnTe contact layer 23 is processed into a mesa stripe shape having a width of 5 μm by chemical etching, and the insulating layer 24 is formed on the p-type ZnSSe layer 20 outside the mesa. . A p electrode 25 made of Pd / Pt / Au is formed on the contact layer 23 and the insulating layer 24, and an I electrode is formed on the substrate 11.
An n electrode 26 made of n is formed.

A semiconductor laser having this structure is used as a resonator 500 μm.
It was cleaved to m and mounted on a copper heat sink with In solder using the p electrode side as a fusion surface, and its characteristics were evaluated.

As a result, the oscillation wavelength is 525 nm,
The oscillation threshold current in continuous operation was 30 mA, and the operating voltage at this time was 2.75V. Further, the maximum oscillation temperature of continuous operation was 80 ° C., and operation was confirmed for 1000 hours or longer at an operating temperature of 50 ° C. and an operating light output of 5 mW, and it was found that the device life was extended 1000 times or more as compared with the conventional device. It was

In the semiconductor laser having the above structure,
The operating voltage of the laser when the density of defects introduced into the n-type ZnSe buffer layer 12 is variously changed is shown in FIG. 3 as already described.

(Second Embodiment) FIG. 2 is a sectional view showing the outline of a semiconductor device (surface-emitting light emitting diode) according to the second embodiment.

As shown in FIG. 2, p-type GaAs substrate 31
On top, a Be-doped p-type GaAs layer 32 (thickness 0.5 μm
m, carrier concentration 2 × 10 ¹⁸ cm ⁻³ ), Be-doped p-type InGaP buffer layer 33 (thickness 0.2 μm), Be-doped p-type InGaAlP buffer layer 34 (thickness 0.2 μm).
m), a Be-doped p-type InAlP buffer layer 35 (thickness: 0.2 μm) is formed.

N-doped p-type Zn is formed on the buffer layer 35.
The Se buffer layer 36 (thickness 30 nm) is formed. In the buffer layer 36, a region 36b other than the circular region 36a corresponding to a region of a circular n-electrode 42 having a diameter of 50 μm described later has a high crystal defect density region (crystal defect density 10 ⁹ c
m ⁻² ) and the circular region 36a constitutes a low crystal defect density region (crystal defect density 10 ⁴ cm ⁻² ). In such a buffer layer 36, the surface region of the buffer layer 35 corresponding to the region 36b is irradiated with an electron beam with an acceleration voltage of 20 kV, and then the entire surface of the buffer layer 35 is N-doped p-type ZnS.
It is formed by growing e. On the buffer layer 36, N-doped CdZ having a thickness of 5 nm and a strain of + 1% is formed.
A multiple superlattice structure (crystal defect propagation stopping layer) 37 is formed by stacking 10 layers each of nSe and a p-type ZnSSe layer having a thickness of 5 nm and -1% strain. N-doped p-type ZnSSe is formed on the crystal defect propagation stopping layer 37.
Clad layer 38 (thickness 0.2 μm), undoped CdZ
nSe quantum well active layer 39 (thickness 10 nm), Cl-doped n-type ZnSSe cladding layer 40 (thickness 2 μm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), Cl-doped n ⁺ -type ZnSe
Contact layer 41 (thickness 0.2 μm, carrier concentration 2 ×
10 ¹⁹ cm ⁻³ ) are sequentially laminated by the MBE method.

The contact layer 41 is processed into a circular shape having a diameter of 50 μm, a Ti / Au electrode 42 is formed thereon, and an Au / AuZn electrode 43 is formed on the back surface of the substrate 41. The conditions for growing the p-type cladding layer 48 are RF output of 150 W and nitrogen flow rate of 0.1 s.
It was set to ccm.

When a current is applied to the surface-emitting LED having this structure, as shown by the arrow in FIG.
On the side), the electric current cannot extract light from the electrode 42.
Since it flows while avoiding the lower region of the, it is possible to efficiently extract light. This is because the region 36a has a low crystal defect density and a current hardly flows, whereas the region 36b has a high crystal defect density and thus a current easily flows.
This LED has a current of 20 mA and a wavelength of 560 n.
A brightness of 5 cd was obtained at m. The brightness of the same LED when the high crystal defect density region was not provided was 1 cd or less under the same conditions. Therefore, the book L
It can be seen that the ED has a significantly improved luminous efficiency.

(Third Embodiment) FIG. 5 is a sectional view showing a schematic structure of a semiconductor device (semiconductor laser) according to a third embodiment of the present invention.

As shown in FIG. 5, an n-type GaAs substrate 51
On the upper side, the thickness is 500 nm and the donor concentration is 2 × 10 ¹⁸ cm ^−3.
The n-type GaAs buffer layer 52 and the n-type GaAlAs buffer layer 53 having a thickness of 500 nm and a donor concentration of 1 × 10 ¹⁸ cm ⁻³ are sequentially formed. On the n-type GaAlAs buffer layer 53, the thickness is 30 nm and the donor concentration is 5 × 10 ¹⁸ c.
A thickness of 5 n is provided through the n − type ZnSe buffer layer 54 of m ^−3.
-1% strained n-type Zn with a donor concentration of 5 × 10 ¹⁸ cm ⁻³ in m
Superlattice defect blocking layer 55 consisting of an SSe layer and a 10 nm + 1% strained n-type ZnMgSSe layer with a donor concentration of 5 × 10 ¹⁸ cm ⁻³ and a donor concentration of 1 × 1 with a thickness of 2 μm.
0 ¹⁸ cm ⁻³ n-type ZnMgSeS cladding layer 56, 100 nm thick n-type ZnSSe optical guide layer 57, thickness 10
nm CdZnSeS single quantum well active layer 58, thickness 1
00 nm p-type ZnSSe light guide layer 59, thickness 2 μm
And p-type ZnMgSS with an acceptor concentration of 4 × 10 ¹⁷ cm ^-3
The e-clad layer 60 is sequentially formed. p-type ZnMg
On the SeS cladding layer 60, a p-type ZnSe layer 61 having a thickness of 100 nm and an acceptor concentration of 1 × 10 ¹⁸ cm ^{−3 and} a p-type ZnSe / ZnTe superlattice contact layer 62 are formed. A thickness of 5 nm is formed on the p-type contact layer 62.
Pt film, 20 nm thick Ti film, 20 nm thick Pt film
A p-electrode 63 is formed by sequentially stacking a film and an Au film having a thickness of 300 nm. And n-type GaAs substrate 51
An n electrode 64 made of Ti / Au is formed on the back surface of the. In the above structure, the ZnMgSeS clad layer 5
6 and 60, ZnSSe optical guide layers 57 and 59 are GaAs
It is formed so as to be substantially lattice-matched to the substrate 51. In the above structure, the n-type ZnSe buffer layer 54 is
It is composed of a peripheral region 54b having a defect density of 1 × 10 ² cm ⁻² and a central region 54a having a defect density of 5 × 10 ⁸ cm ⁻² .

The semiconductor laser configured as described above can be manufactured, for example, as follows. First, the GaAs buffer layer 52 is formed by molecular beam epitaxy (MBE).
And a GaAlAs buffer layer 53 are grown in a III-V compound semiconductor growth chamber. The growth temperature was 600 ° C., and the ratio of the group V element (As) to the group III element (Ga, Al) (V / group III element ratio) was 10. The growth was completed by first closing the shutter of the group III element, passivating the growth surface with As, and then closing the shutter of As. Then 3
The temperature was lowered to below 00 ° C. Next, the acceleration voltage 20
A 5 μm wide stripe-shaped portion was scanned with an electron beam of KV. By irradiating with an electron beam, As that is passivated on the surface is evaporated and the Ga and Al surfaces are exposed. The wafer thus treated was transferred to a II-VI group compound semiconductor growth chamber through an ultra-vacuum transfer system to grow a ZnSe layer 54. By performing the above-described processing, the defect density is 5 × in the part irradiated with the electron beam.
It was 10 ⁸ cm ^-2 (central region 54a), and the defect density of the portion not irradiated with the electron beam could be 1 × 10 ³ cm ^-2 . This is because As is evaporated by the electron beam and damage is introduced, so that the defect density can be controlled in this way. That is, A
In the portion where s has evaporated, three-dimensional growth occurs when growing ZnSe, and many defects are introduced. On the other hand, ZnSe is two-dimensionally grown in the portion that is passivated with As to suppress the generation of defects. Subsequently, the layer structure as shown in FIG. 5 was sequentially grown.
After the growth was completed, a sample was taken out and a Pt / Ti / Pt / Au electrode metal was vapor-deposited on the p-type ZnTe layer 62 by an electron beam vapor deposition method to form a p-side electrode 63. In the structure of the present embodiment, the contact area of the p-electrode 63 can be remarkably large as compared with the conventional example in which it is difficult to manufacture the current confinement structure, so that the contact resistance can be reduced and good ohmic contact can be achieved. I found that was obtained. Also,
An In electrode is vapor-deposited on the back surface of the n-type GaAs substrate 51.
The electrode 64 was formed. After forming the electrode metal, 400 ° C, 10
Annealing was performed for about 2 seconds.

A semiconductor laser having the above structure is used as a resonator length 500.
After cleaving to μm, a p-electrode 63 side was used as a fusion surface to mount on a copper heat sink using In solder, and its characteristics were evaluated. When a current is passed through the light emitting diode having the structure shown in FIG. 5, the current preferentially flows through the central portion corresponding to the region 54a, as indicated by the arrow in FIG. As a result, the oscillation wavelength is 520 nm, and the continuous operation produces an oscillation threshold current of 35 mA.
It was a good one. The operating voltage at this time was 3 V, and the maximum oscillation temperature during continuous operation was 70 ° C. That is, according to the present embodiment, it is possible to reduce the operating voltage by realizing an effective current constriction structure,
Continuous oscillation was obtained at a temperature sufficiently higher than room temperature, which was difficult in the past. Further, by providing the superlattice defect blocking layer 55, defects in the n-type ZnSe layer are blocked by this layer and do not reach the active layer, and high reliability was obtained.
Actually, at an operating temperature of 40 ° C and an operating light output of 3 mW, 1
The operation was confirmed for more than 000 hours. In the structure of the present embodiment, ZnSe is described as an example of a layer having a different defect density, but similar effects can be obtained with Cd, Zn, Mg,
It was also obtained by a combination of other wide gearup II-VI group compound semiconductors composed of Te, Se, S and the like. Further, although an example in which the ZnSe layer is grown on the n-type GaAlAs layer is shown, the same effect can be obtained by directly growing the ZnSe layer on the GaAs layer. Further, it is needless to say that a good current constriction effect and reliability can be obtained even in a structure in which the conductivity type is reversed using a p-type substrate. Further, in the present embodiment, the electron beam was irradiated to evaporate As, but the same effect can be obtained by converging and using a laser beam or a mercury lamp.

(Fourth Embodiment) FIG. 6 is a sectional structural view of a semiconductor device (light emitting diode) according to a fourth embodiment.

As shown in FIG. 6, a p-type GaAs substrate 71
On top, the thickness is 500 nm and the acceptor concentration is 1 × 10 ¹⁸ c.
m ⁻³ p-type GaAs buffer layer 72, p-type InGaAlP having a thickness of 500 nm and an acceptor concentration of 1 × 10 ¹⁸ cm ⁻³
The puffer layer 73 is sequentially formed.

On the p-type InGaAlP buffer layer 73, a p-type ZnSe buffer layer 74 having a thickness of 30 nm and an acceptor concentration of 1 × 10 ¹⁸ cm ⁻³ is interposed, and a thickness of 5 nm and a concentration of 7 × 10 ¹⁷ cm ⁻³ . Superlattice defect blocking layer 75 formed by stacking 10 layers each of a -1% strained p-type ZnSSe layer and a thickness of 5 nm and an acceptor concentration of 5 × 10 ¹⁷ cm ^{-3 and} a + 1% strained p-type ZnMgSSe layer, each having a thickness of 2 μm. 5x concentration
10 ¹⁷ cm ⁻³ p-type ZnMgSeS cladding layer 76, 100 nm-thick p-type ZnSSe optical guide layer 77, thickness 1
0 nm CdZnSeS single quantum well active layer 78, 100 nm thick n-type ZnSSe optical guide layer 79, 2 μm thick
n-type ZnMgSSe with a donor concentration of 1 × 10 ¹⁸ cm ⁻³ in m
Clad layer 80, thickness 100 nm, donor concentration 1 × 10
¹⁸ cm ⁻³ n-type ZnSSe layer 81, and donor concentration 1 ×
An n-type ZnSe contact layer 82 of 10 ¹⁹ cm ^-3 is sequentially formed.

In the above structure, the ZnMgSeS cladding layers 76 and 80 and the ZnSSe optical guide layers 77 and 79 are G.
It is formed so as to be substantially lattice-matched to the aAs substrate 71. In addition, in the above structure, the p-type ZnSe buffer layer 7
4 is composed of a peripheral region 74a having a defect density of 1 × 10 ³ cm ⁻² and a central region 74b having a defect density of 5 × 10 ⁸ cm ⁻² .

The semiconductor laser thus configured is manufactured as follows. First, the molecular beam epitaxy method (MB
E), the GaAs buffer layer 72 and the InGaAlP
The buffer layer 73 was grown in the III-V compound semiconductor growth chamber. The growth temperature is 600 ° C., the group V element (As, or
P) and the group III element (In, Ga, Al) ratio (V / III
The group element ratio) was set to 10. The growth was completed by first closing the shutter of the group III element, passivating the growth surface with P, and then closing the shutter of P. Then 30
The temperature was reduced to below 0 ° C. Next, the acceleration voltage 20
A KV electron beam was scanned on a circular portion having a diameter of 50 μm. By irradiating with an electron beam, P passivated on the surface evaporates, and the In, Ga, Al surfaces are exposed. The wafer thus treated was transferred to the II-VI group compound semiconductor growth chamber through the ultra-vacuum transfer system to grow the ZnSe layer 74. By performing the above-described processing, the defect density is 5 × in the part irradiated with the electron beam.
It was 10 ⁸ cm ^-2 (region 74b), and the defect density of the portion not irradiated with the electron beam could be 1 × 10 ³ cm ^-2 . This is because P is evaporated by the electron beam and ZnSe is three-dimensionally grown, and damage is introduced by the electron beam, so that the defect density can be controlled in this way. After the growth was completed, the sample was taken out and n-type Zn
An n electrode 83 having a diameter of 50 μm was formed on the Se contact layer 82 concentrically with the region 74b. n electrode has a thickness of 2
A 0 nm Ti film and a 300 nm thick Au film are sequentially laminated. Then, on the back surface of the p-type GaAs substrate 71, Ti
A p-electrode 84 made of / Au was formed. After electrode formation, 4
Annealing was performed at 00 ° C. for about 10 seconds.

The light emitting diode having the above structure was cut into a pellet of 300 μm square, and its light emitting characteristic was evaluated.
When a current is passed through the light emitting diode having the structure shown in FIG. 6, as shown by an arrow in FIG. 6, the current flows by avoiding the lower part of the n-electrode 83 where the light cannot be extracted, so that the light is efficiently extracted. be able to. As a result, the emission efficiency is 1.5 at an emission wavelength of 520 nm and an operating current of 20 mA.
It was as good as%. The operating voltage at this time was 3V. Also, at operating current of 20 mA, 1
The decrease in luminous efficiency after continuous operation for 000 hours is 5% of the initial level.
And few. That is, according to this example, a light emitting diode having a low operating voltage and a high efficiency, which was difficult in the past, was obtained, and its reliability was sufficiently put to practical use. In the structure of this embodiment, ZnSe has been described as an example of the II-VI group compound semiconductor layer for controlling defects, but similar effects can be obtained by using Cd, Zn, Mg, Te, Se, S and the like. It was also obtained by combination with wide-gap II-VI compound semiconductors. In addition, good luminous efficiency and reliability were also obtained for the structure with the opposite conductivity type.

As described above, even when the same GaAs substrate is used for growing the ZnSe type thin film, As is used as the buffer layer.
The relationship between the crystal defect density at the interface and the ease of current flow is reversed depending on whether the system material or the P system material is used.

In this embodiment, the semiconductor laser and the light emitting diode are taken as an example. However, it is generally effective as a structure of an element for injecting current, and it is effective even when used for an electronic device such as a hetero bipolar transistor. I was seen. Other various modifications can be made without departing from the scope of the present invention.

(Fifth Embodiment) FIG. 7 already described.
The semiconductor element of (b) constitutes the fifth embodiment.

(Sixth Embodiment) FIG. 9 shows a schematic sectional view of a semiconductor laser according to a sixth embodiment.

As shown in FIG. 9, the structure of the semiconductor laser has the same structure as the semiconductor laser structure shown in FIG. 1 except that an n-type GaAs buffer layer is provided between the substrate 11 and the ZnSSe layer 12. The same parts are designated by the same reference numerals and the description thereof will be omitted. However, in this embodiment, the ZnMgSSe layer forming the multiple superlattice structure 15 is similarly Cl.
However, unlike the conventional Cl, the ZnSSe layer is doped with I according to the present invention.

When a conventional multiple superlattice structure including a Cl-doped ZnSSe layer is provided, the effective donor concentration measured by capacitance-voltage is 7 × 10 ¹⁷ cm ^-3 at the maximum, and the operating voltage of the device is 10 V or more. On the other hand, in the semiconductor laser of the sixth embodiment, it was confirmed that the operating voltage can be reduced to 3V and the life thereof is about 1000 times that of the conventional one.

If the semiconductor laser structure shown in FIG. 9 has a p-type region under the active layer 17, the superlattice structure 15 is ZnS doped with As according to the present invention.
The same effect can be obtained by using ZnMgSSe doped with Se and N.

The high-concentration doping of the present invention is not limited to the above example, but can be applied to various other semiconductor devices. For example, the present invention can be applied to the production of a semiconductor device made of a III-V group compound semiconductor such as GaAs (for example, a red semiconductor laser), more specifically, a device based on a combination of InGaP and InGaAsP, or a superlattice.

As an example, InG on a GaAs substrate
Considering the case of doping the aP layer, InGa
Depending on the composition of the P layer, the lattice constant may be larger or smaller than that of the GaAs substrate. However, when the same type of dopant is used as the n-type or p-type dopant for both layers, high concentration doping is performed in both layers. It is difficult to achieve.

On the other hand, according to the present invention, when the InGaP layer has a larger lattice constant than the GaAs substrate, S, Se, C, Si, Ge or the like is used as the n-type dopant,
High-concentration doping can be achieved by using Be, Mg, Zn, or the like as the p-type dopant. Also, InGa
If the P layer has a smaller lattice constant than the GaAs substrate,
High-concentration doping can be achieved by using Te, Sn or the like as the n-type dopant and using Cd, Sr or the like as the p-type dopant.

Furthermore, the high-concentration doping of the present invention can be applied to the case of manufacturing a GaN semiconductor laser. G
In the aN semiconductor laser, GaN, In are used as the active layer.
By using GaN, InN, or the like, it is possible to emit light in a substantially visible light region to a near-ultraviolet region with an oscillation wavelength of 0.37 to 0.65 μm at room temperature. Further, as the clad layer, AlGaN or the like is regarded as promising. Hereinafter, a case of performing high-concentration doping on an InGaAlN quaternary mixed crystal that is a mixed crystal will be described.

When sapphire or SiC having a small lattice constant is used as the substrate, Mg is generally used as the p-type dopant for InGaAlN, but according to the present invention, Be or C having a small atomic radius was used as the dopant. Higher concentration doping can be achieved. Also, n
As the type dopant, according to the present invention, C, Si, S, O
High-concentration doping can be achieved by using such as.
However, since group IV elements such as C and Si are amphoteric elements,
Depending on the crystal growth conditions, it can act as both a donor and an acceptor.

Further, GaAs having a large lattice constant is used as the substrate.
According to the present invention, when using, as a dopant to InGaAlN, as a p-type dopant, Ca, S
Ge, Sn, P as an n-type dopant such as r and Ba.
High-concentration doping can be achieved by using b, Se, Te, or the like.

Furthermore, when ZnO is used as the substrate,
InGaAlN may have a larger lattice constant or a smaller lattice constant with respect to the ZnO substrate depending on its composition.
In the case where InGaAlN has a larger lattice constant than the ZnO substrate, the same dopant as in the case of using sapphire or SiC as the substrate is used, and InG is more used than the ZnO substrate.
When aAlN has a smaller lattice constant, high-concentration doping can be achieved by using the same dopant as that when GaAs is used as the substrate.

(Seventh Embodiment) FIG. 10 shows a schematic sectional view of a GaN-based blue semiconductor laser according to the seventh embodiment.

In order to manufacture this semiconductor laser, first,
A portion (1) covered with SiO ₂ in a stripe shape (not shown)
01a) and an exposed portion (101b) not covered with SiC (1120) (a surface) substrate 101 is caused to flow a plasma gas or the like to selectively deteriorate the exposed portion of the surface of the substrate 101. Then, the striped SiO ₂ film is removed using ammonium fluoride or the like. An SiC buffer layer 10 having a thickness of about 500 nm is formed on the surface of the substrate 101 by using disilane and acetylene by the CVD method.
2 is formed, and a growth temperature of 510 is obtained by the MOCVD method.
At 20 ° C., hydrogen is used as a carrier gas, and ammonia and trimethylgallium (TMG) are used as source gases to form a GaN buffer layer 103 having a thickness of about 20 nm. After that, the flow of only TMG is stopped and the temperature is raised to 1030 ° C. At 1030 ° C., TMG and ammonia gas are used as source gases, and silane gas is used as a dopant to form a Si-doped n-type GaN layer 104 to a thickness of 3 μm. Then, Si-doped n-type GaAlN is prepared by using TMG, trimethylaluminum (TMA) and ammonia as source gases and silane gas as a dopant gas.
(Al composition ratio 30%) The cladding layer 105 is grown to a thickness of 500 nm. On this clad layer 105, a crystal defect propagation blocking layer 106 having a multistrain superlattice structure composed of n-type AlGaN and n-type InGaN is formed in order to block the propagation of dislocations generated at the interface between the substrate and the growth layer. Form. Since AlGaN and InGaN have larger bond radii of covalent bonds between the mother elements than the SiC substrate, according to the present invention, elements such as Si, O, and S having a small atomic radius are added to the crystal defect propagation blocking layer 106 as n-type dopants. High concentration doping is achieved by using the

Then, TMG, trimethylindium (TMI), and ammonia were used as source gases to a thickness of 1
00 nm undoped InGaN (In composition ratio 10%)
The active layer 107 is formed. On top of that, as source gas,
TMG, TMA and ammonia with a thickness of 50 using cyclopentadienyl magnesium as a dopant gas.
0 nm Mg-doped p-type GaAlN (Al composition ratio 30
%) The clad layer 108 is formed. After that, thickness 50
A 0 nm Mg-doped p-type GaN contact layer 109 is formed. The p-type GaN contact layer 109 has a thickness of 300 nm by controlling the stripe width by the SiO ₂ film 110.
Electrode 1 having a laminated structure of Ni and Au having a thickness of 1 μm
11 is formed. Further, on the entire back surface of the substrate 101, an electrode 112 having a laminated structure of Ni having a thickness of 300 nm and Au having a thickness of 1 μm is formed.

In the laser diode having the above structure, the substrate 1
In the surface region 101b of No. 01, the crystal defect density at the interface between the substrate and the growth layer is low (10 ⁴ cm ⁻² ), so that the voltage drop at the interface is large, whereas in the deteriorated surface region 101a, the substrate and the growth layer 101b. High density at the interface with (10 ⁸ cm ^-2 or more)
Since the crystal defect of No. 2 exists, the voltage drop at the interface is small, so that the current selectively flows only in the surface region 101a. Therefore, a current is efficiently injected into the active layer 107, and a device that performs laser oscillation at a low threshold voltage is provided.

The method of introducing high density crystal defects is as follows.
It is not limited to the above. For example, high density crystal defects can be introduced by forming a portion that is selectively carbonized and a portion that is not carbonized by using methane, propane, acetylene, or the like on the surface of the SiC substrate 101. In this case, in the carbonized portion, the crystal defect density is low, and it becomes difficult for current to flow,
In the portion that is not carbonized, the crystal defect density is high, and the current easily flows. In addition, the high-density crystal defects can be introduced by the electron beam irradiation described above.

(Eighth Embodiment) FIG. 11 shows a schematic sectional view of a GaN-based blue semiconductor laser according to an eighth embodiment.

This semiconductor laser uses GaAs as a substrate.
It has the same structure as the semiconductor laser shown in FIG. 10 except that the (100) substrate or the Si substrate 201 is used and the SiC buffer layer 102 is not formed. 11, those parts which are the same as those corresponding parts in FIG. 10 are designated by the same reference numerals, and a description thereof will be omitted.

In the semiconductor laser shown in FIG. 11, G
By selectively forming an As plane on the surface of the aAs substrate 201, a region 201a having a low crystal defect density is provided.
Region 201 having a high crystal defect density without forming an s-plane
b is provided. In the GaN-based semiconductor layer (zinc blende type crystal) formed on the GaAs substrate, at the interface between the substrate and the semiconductor layer, contrary to the case of the seventh embodiment, a high density (10 ⁸ cm ^{− 2} or more) In the crystal defect region 210b,
In the region where the density of crystal defects is low (10 ⁴ cm ^-2 or less), the voltage drop at the interface is small, so that the current selectively flows.

In the semiconductor laser shown in FIG. 11, the multi-strained superlattice structure 105 uses GaAs as a substrate and is composed of AlGaN and InGaN having a bond radius of covalent bond between mother elements smaller than that of the substrate. High-concentration doping is achieved by using Se, Sn, Ge or the like having a small atomic radius as the type dopant.

[0068]

As described above, according to the present invention,
A semiconductor device that can be driven with a low operating voltage is provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the crystal defect density in the n-type ZnSe buffer layer and the operating voltage in the first aspect of the present invention.

FIG. 4 is a graph showing a relationship between a crystal defect density in an n-type ZnSe layer formed on an n-type GaAs substrate via an InGaAlP buffer layer and an operating voltage.

FIG. 5 is a schematic sectional view of a semiconductor device according to a third embodiment of the present invention.

FIG. 6 is a schematic sectional view of a semiconductor device according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing effective donor or acceptor concentration in each layer of a semiconductor element.

FIG. 8 is a diagram showing the degree of lattice mismatch between a GaAs substrate and a semiconductor layer in relation to the effective donor or acceptor concentration.

FIG. 9 is a sectional view of a semiconductor device according to a sixth embodiment of the present invention.

FIG. 10 is a sectional view of a semiconductor device according to a seventh embodiment of the present invention.

FIG. 11 is a sectional view of a semiconductor device according to an eighth embodiment of the present invention.

[Explanation of symbols]

11, 31, 51, 71, 101, 201 ... Substrate, 1
2, 36, 54, 74, 102 ... Buffer layer, 15, 3
7, 55, 75, 106 ... Superlattice structure.

Front page continuation (72) Inventor Shinji Saito 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (4)

[Claims] 1. A semiconductor comprising a semiconductor substrate and a semiconductor layer formed on the semiconductor substrate, wherein the semiconductor layer has a defect density of at least 1 × 10 ⁸ cm ⁻² or more. element. 2. A semiconductor having a semiconductor substrate and a semiconductor layer formed on the semiconductor substrate, wherein the semiconductor layer has a defect density of at least 1 × 10 ⁴ cm ⁻² or less. element. 3. A semiconductor substrate, and a semiconductor layer formed on the semiconductor substrate, wherein the semiconductor layer is 1 × 10 ⁸ c.
A semiconductor device comprising a portion having a defect density of m ⁻² or more and a portion having a defect density of 1 × 10 ⁴ cm ⁻² or less. 4. A semiconductor substrate, and a semiconductor layer formed on the semiconductor substrate, wherein a bond radius of a covalent bond between mother elements constituting the semiconductor layer is a covalent bond between mother elements constituting the substrate. When the bond radius is larger than the bond radius of, the impurities having an atomic radius smaller than the bond radius, or the bond radius of the covalent bond between the mother elements forming the semiconductor layer is shared between the mother elements forming the substrate. A semiconductor device, wherein the semiconductor layer is doped with an impurity having an atomic radius larger than the bond radius when the bond radius is smaller than the bond radius.