JPH0992936A - Semiconductor laser device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a highly reliable semiconductor laser device capable of reducing a potential barrier of a carrier block layer and reducing a driving voltage. A second n-type clad layer 31, a first n-type clad layer 32, an n-type carrier block layer 33, an active layer 34 having a double quantum well structure, and A on a semiconductor substrate 40 in this order.
The p-type carrier block layer 35, the first p-type clad layer 36, and the second p-type layer whose l composition ratio is distributed trapezoidally along the layer thickness direction.
A type clad layer 37 and a p-type contact layer 39 are formed respectively. A current constriction layer is embedded in the p-type contact layer 39 so as to sandwich the central stripe portion from both sides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to optical communication, optical recording of optical disks, optical information processing, laser printers, laser processing,
The present invention relates to a semiconductor laser device that is suitable for use in laser medicine and that can operate with high efficiency and high output.

[0002]

2. Description of the Related Art In order to increase the output of a semiconductor laser, a carrier block layer having a large forbidden band width and a thickness small enough not to disturb the guided mode is provided on both sides of the active layer so that the carrier block layer is provided outside the carrier block layer. A semiconductor laser capable of providing an independent waveguiding mechanism has been proposed.
In such a structure, the carrier block layer has a function of efficiently confining the injected carriers in the active layer, and since the carrier block layer is formed thin,
It does not affect the guided mode control by the guiding mechanism formed on the outside. Therefore, guided mode control completely independent of carrier confinement is possible. Therefore, by expanding the waveguide mode,
Instantaneous optical damage caused by local concentration of laser light can be prevented, and the end face destruction level can be increased, so that high output operation can be realized.

FIG. 12A is a sectional view showing an example of a semiconductor laser having a carrier block layer.
(B) Distribution map of forbidden band width corresponding to each layer, FIG.
(C) is a distribution diagram of the refractive index corresponding to each layer. Such a structure is a well-known separated confinement heterostructure (SC) formed by separating a carrier confinement region and an optical confinement region.
H, Separate Confinement Heterostructure), the carrier block layer is used to complete carrier confinement.
rfect SCH) (International publication WO93 / 1651)
No. 3).

In FIG. 12A, a second n-type clad layer (n-AlGaAs) 1 and a first n-type clad layer (n-AlGaAs) 2 are sequentially formed on a semiconductor substrate (not shown) made of n-GaAs. , N-type carrier block layer (n
-AlGaAs) 3, active layer (GaAs / AlGaA)
s) 4, p-type carrier block layer (p-AlGaAs)
5, first p-type cladding layer (p-AlGaAs) 6, second
P-type clad layers (p-AlGaAs) 7 are formed respectively.

As shown in FIG. 12B, the forbidden band width of each carrier block layer 3, 5 is formed so as to be larger than any of the active layer 4 and each of the cladding layers 1, 2, 6, 7. As a result, the injected carriers are efficiently injected into the active layer 4.
Trapped in. Therefore, the number of carriers that contribute to laser oscillation increases, and the oscillation efficiency improves.

Further, as shown in FIG. 12C, each layer from the first n-type cladding layer 2 to the first p-type cladding layer 6 is a high refractive index portion, and the second n-type cladding layer 1 and the second p-type cladding layer 7 are formed. Since the slab waveguide structure that forms the low refractive index portion is formed, the light generated in the active layer 4 spreads and propagates in the high refractive index portion. Therefore, the optical peak intensity at the emission end face is reduced, optical damage is less likely to occur, and high output operation becomes possible.

[0007]

In a conventional semiconductor laser of complete isolation confinement heterostructure (PSCH), n
In order for the type carrier block layer to function as a hole block and the p type carrier block layer to function as an electron block, it is necessary to raise the energy band by highly doping the carrier block layer.

FIG. 13 (a) is an energy band diagram of a PSCH semiconductor laser, FIG. 13 (b) is an enlarged view near the n-type carrier block layer, and FIG. 13 (c) is an enlarged view near the p-type carrier block layer. Is. Spike-like potential barriers are formed at the conduction band hetero interface in the n-type carrier block layer and at the valence band hetero interface in the p-type carrier block layer.

A certain amount of energy is required for the injected electrons to get over the potential barrier formed in the conduction band, and similarly, for the injected holes to get over the potential barrier formed in the valence band. Therefore, it is necessary to give extra energy to electrons and holes,
This results in an increase in the driving voltage of the semiconductor laser.

Further, when carriers that have surpassed such a potential barrier are relaxed to the quantum well layer, the excess energy is changed into heat, which increases the temperature of the active layer and becomes a factor of lowering the reliability of the semiconductor laser.

It is an object of the present invention to provide a highly reliable semiconductor laser device capable of reducing the potential barrier generated at the hetero interface of the carrier block layer and reducing the driving voltage.

[0012]

According to the present invention, a clad layer is provided on both sides of an active layer, and the active layer and a carrier block layer having a forbidden band width equal to or greater than the forbidden band width of the clad layer are provided in the active layer. A semiconductor laser device, which is provided in close proximity to the carrier block layer, in which a region in which a forbidden band width decreases along the layer thickness direction from the inside of the layer toward the bonding surface with the adjacent layer is formed. Is. Further, in the present invention, the region where the forbidden band width of the carrier block layer is maximum is at least 4 of the carrier tunnel length.
It is characterized by having a double thickness. Further, the present invention is characterized in that the forbidden band width at the joint surface of the carrier block layer is equal to or larger than the forbidden band width of an adjacent layer adjacent to the carrier block layer. In the present invention, the n-type clad layer and the p-type clad layer each include a first clad layer and a second clad layer in the order of being closer to the active layer, where π is the circular constant, λ is the oscillation wavelength, and the first clad layer is Is defined as V = (π · d1 / λ) · (N1 ² −N2 ² ) ^0.5 , where N1 is the maximum refractive index of N2 and d1 is the effective thickness between the second cladding layers, and N2 is the refractive index of the second cladding layer. At this time, V> π / 3. Here, when the refractive index of the first cladding layer is constant, the maximum refractive index N1 has the constant value, but when the refractive index has a distribution in the first cladding layer, it means the maximum value. In addition, the effective thickness d1 is the second
The refractive index at an arbitrary position (x) between the cladding layers is Nw
If the position of the interface of the second n-type clad layer close to the active layer is x1 and the position of the interface of the second p-type clad layer close to the active layer is x2, it is determined by the following equation.

[0013]

[Equation 1]

[0014]

According to the present invention, by forming a region in the carrier block layer in which the forbidden band width decreases along the layer thickness direction from the inside of the layer toward the bonding surface, the spike generated at the hetero interface of the carrier block layer is formed. The height of the potential barrier can be kept low. Therefore, the carriers easily move into the active layer, it is not necessary to increase the driving voltage of the semiconductor laser, and extra heat generation can be suppressed.

The details will be described below. 1A and 1B are energy band diagrams of a heterojunction between a p-type semiconductor having a forbidden band width of Eg1 and a p-type semiconductor having a forbidden band width of Eg2. FIG. Directly bonded to each other, Fig. 1
(C) shows a state in which a region in which the forbidden band width changes along the layer thickness direction is provided and joined.

Before the heterojunction, as shown in FIG. 1 (a), the forbidden band widths of both are in a relationship of Eg1 <Eg2, and both conductivity types are p-type, so the Fermi level is near the valence band. It is formed.

When both are directly bonded, the potential distribution changes when the holes near the bonding interface move from the wide bandgap side to the narrow bandgap side so that the Fermi levels of the two match. The energy band is changed to that shown in 1 (b), and a spike-like potential barrier is formed at the junction interface of the valence band. In this state, extra energy is required to overcome the potential barrier when the hole moves to the left in the figure.

On the other hand, when the region K in which the forbidden band width continuously changes from Eg2 to Eg1 is provided along the layer thickness and the junction is made, the energy band shown in FIG. The height of the potential barrier at the bonding interface of the strip can be suppressed to a low level. Therefore, when the hall moves to the left in the figure,
Can easily pass through the potential barrier.

FIG. 2 is a band diagram near the p-type carrier block layer of the PSCH semiconductor laser. In the PSCH semiconductor laser, holes get over the potential barrier formed in the valence band and are injected into the quantum well layer. In the conduction band, the p-type carrier block layer blocks the movement of electrons.

The Al (aluminum) composition ratio of the conventional p-type carrier block layer is rectangular, and the valence band has a spike-like potential shape at both interfaces of the carrier block layer. However, in the present invention, by forming the Al composition ratio of the p-type carrier block layer into, for example, a trapezoidal type, the valence band becomes a potential shape that is gently inclined at both interfaces of the carrier block layer, and the peak is suppressed, and the hole is suppressed. Will be easier to move.

Although the p-type carrier block layer has been described here, the same theory holds for the n-type carrier block layer, in other words, holes are electrons and valence bands are conduction bands. That is, a potential barrier for electrons is formed on the conduction band side at the junction interface of the n-type carrier block layer, but the height of the barrier is increased by interposing the region K where the forbidden band width changes along the layer thickness direction. Can be suppressed.

FIG. 3 is a distribution diagram schematically showing the Al composition ratio of the PSCH semiconductor laser. Since the carrier block layer has a large forbidden band width, the Al composition ratio also becomes large. Since carriers are concentrated in the quantum well layer, the forbidden band width is smallest and the Al composition ratio is also small.

FIG. 4 is a distribution chart showing an example of the Al composition ratio of the carrier block layer according to the present invention. In FIG. 4A, the distribution shape of the conventional Al composition ratio is rectangular (thickness D
0), but in the present invention, a rectangular shape with both corners chamfered, that is, A is formed inside the carrier block layer.
A region having a flat l composition ratio (thickness D2) and a region (thicknesses D1 and D3) in which the Al composition ratio linearly decreases along the layer thickness direction from the inside of the layer toward the bonding surface are formed. In addition, Al
The relationship between the composition ratio and the forbidden band width is not directly proportional, but the larger the Al composition ratio, the larger the forbidden band width.

In FIG. 4 (b), the distribution shape of the Al composition ratio is trapezoidal, and the region where the Al composition ratio is flat (thickness D
2) and has A along the layer thickness direction from inside the layer toward the joint surface.
The l composition ratio linearly decreases, and regions (thicknesses D1 and D3) are formed at the interface so as to match the Al composition ratio of the adjacent layer.

The thicknesses D1 and D3 are preferably equal to or less than the internal thickness D2, but due to the function of the carrier block layer, it is four times or more the electron tunnel length in the case of n-type, and the hole tunnel in the case of p-type. It is preferable to have a thickness D2 that is at least four times the length. Further, it is preferable that the forbidden band width at the bonding surface of the carrier block layer is equal to or larger than the forbidden band width of the adjacent layer adjacent to the carrier block layer. As a result, the carrier is surely blocked and the band gap is smoothly connected.

FIG. 5 is a distribution chart showing another example of the Al composition ratio of the carrier block layer according to the present invention. FIG. 5 (a)
Has a flat portion which is about four times as long as the tunnel length of carriers, and forms a region in which the forbidden band width decreases linearly in the layer thickness direction from the inside of the layer toward the junction surface. FIG. 5 (b)
Has a forbidden band width reduced stepwise along the layer thickness direction from the inner flat portion toward the joint surface. FIG. 5C is a diagram of FIG.
The number of steps in (b) is two, and it may be configured with three or more steps. FIG. 5D is an example in which the Al composition ratios are asymmetrically distributed. In FIG. 5E, the Al composition ratio changes linearly along the layer thickness direction, and the slope of the change region is 2
This is an example where there are types.

FIG. 6 is an explanatory diagram showing the carrier block layer thickness dependence of the electron tunneling probability. In general, the probability that a particle will tunnel a rectangular potential barrier is uniquely determined if the height and width of the potential barrier, the mass of the particle, and the energy of the particle are determined (Kyoritsu Shuppan Kenichi Goto, et al., "Quantum Mechanics Exercise", page 55). ).

Therefore, the average kinetic energy of the carrier = k
The tunnel length is defined as the film thickness at which the carrier tunnel probability at T / 2 is 1 / e. For example, A1 of the carrier block layer
When the composition ratio is 0.6 and the A1 composition ratio of the cladding layer adjacent thereto is 0.3, the electron tunnel length can be calculated as shown in FIG.

Further, the n-type and p-type clad layers are composed of a plurality of clad layers of a first clad layer and a second clad layer in order of being closer to the active layer, and further, an active layer and a carrier sandwiched by the second clad layer. By forming the standardized frequency V of the optical waveguide including the block layer and the first cladding layer to be larger than π / 3, it is possible to approximate the waveguide mode to the ideal Gaussian type. Further, the peak intensity of the guided mode in the active layer region is reduced, and the optical damage level at the emitting end face of the semiconductor laser device can be increased. Further, in order to prevent the multi-mode, the normalized frequency V is preferably 2π or less.

[0030]

【Example】

(Embodiment 1) FIG. 7A is a sectional view showing an embodiment of the present invention, and FIG. 7B is a distribution chart showing the Al composition ratio of the p-type carrier block layer 35.

In FIG. 7A, a semiconductor substrate 4 made of n-GaAs is formed by using a thin film manufacturing method such as MOCVD (metal organic chemical vapor deposition) or MBE (molecular beam growth).
0, a second n-type clad layer (thickness 0.7 μm) 31 made of n-Al _0.48 Ga _0.52 As, and n-Al.
_A first n-type cladding layer (thickness 0.4 μm) 32 made of _0.30 Ga _0.70 As, an n-type carrier block layer (thickness 0.015 μm) 33 made of n-Al _0.60 Ga _0.40 As, 33
Active layer 34 having a double quantum well structure (DQW) made of GaAs / Al _0.30 Ga _0.70 As, p-Al _0.60 Ga
A p-type carrier block layer (thickness 0.025 μm) 35 made of _0.40 As and having an Al composition ratio of trapezoidal type, p-Al _0.30 G
a _0.70 As first p-type cladding layer (thickness 0.4 μm
m) 36, a second p-type clad layer (thickness 0.7 μm) 37 made of p-Al _0.48 Ga _0.52 As, and p-GaA
A p-type contact layer (thickness 2 μm) 39 made of s is formed. The p-type contact layer 39 has a current confinement layer (thickness: 0.3 μm) made of n-GaAs.
m) 38 is embedded so as to sandwich the central stripe portion from both sides.

Ohmic electrodes 41 and 42 are formed on the upper surface of the p-type contact layer 39 and the lower surface of the semiconductor substrate 40. The resonance direction of light is perpendicular to the paper surface of FIG. 7A, and the cavity end surface of the semiconductor laser device is formed parallel to the paper surface of FIG. 7A.

As shown in FIG. 7 (b), the distribution of the Al composition ratio x of the p-type carrier block layer 35 shows a trapezoidal shape, the inner flat portion is x = 0.6 and the thickness is 150Å. The region where the Al composition ratio decreases along the layer thickness direction is x = 0.3 and the thickness is 50Å. Therefore, the distribution shape of the forbidden band width of the p-type carrier block layer 35 also has a shape similar to a trapezoid. With such a configuration, the height of the potential barrier generated at both junction interfaces of the p-type carrier block layer 35 can be reduced, holes easily move in the valence band, and the injection efficiency into the active layer 34 is improved.

FIG. 8 is a graph showing the current-voltage characteristics of the semiconductor laser device. FIG. 9 is a distribution diagram of the Al composition ratio of the p-type carrier block layer, FIG. 9A is Example 1 of FIG. 7, and FIG. 9B is Comparative Example 1. Both Example 1 and Comparative Example 1 shown in FIG. 7 have the same condition that the cavity length is 900 μm, the current injection stripe width is 50 μm, and the optical coating has a reflectance of 10% on the front surface and a reflectance of 96% on the rear surface. The p-type carrier block layer of Comparative Example 1 has a thickness of 200.
Å, and the Al composition ratio is uniform.

It can be seen from the graph of FIG. 8 that the driving voltage in Example 1 is reduced by about 10% as compared with Comparative Example 1.

(Embodiment 2) FIG. 10A shows a second embodiment of the present invention.
10 (b) is a distribution diagram showing the Al composition ratio of the p-type carrier block layer 35. FIG.

In FIG. 10A, a thin film manufacturing method such as MOCVD (Metal Organic Chemical Vapor Deposition) or MBE (Molecular Beam Growth) is used to sequentially form n layers on a semiconductor substrate 40 made of n-GaAs. -Al _0.27 Ga _0.73 As second n-type cladding layer (thickness 1.2 μm) 31, n-Al
_A first n-type clad layer (thickness 0.49 μm) 32 made of _0.10 Ga _0.90 As, an n-type carrier block layer (thickness 0.03 μm) 33 made of n-Al _0.40 Ga _0.60 As, and having an Al composition ratio of trapezoid 33, In _0.18 Ga _0.88 As / Al _0.10
An active layer 34 having a double quantum well structure (DQW) made of Ga _0.90 As, p-Al _0.40 Ga _0.60 As made of Al
The trapezoidal p-type carrier block layer (thickness 0.0
3 μm) 35, first composed of p-Al _0.10 Ga _0.90 As
p-type clad layer (thickness 0.49 μm) 36, p-Al
_A second p-type clad layer (thickness 1.2 μm) 37 made of _0.27 Ga _0.73 As and a p-type contact layer (thickness 2 μm) 39 made of p-GaAs are formed. A current confinement layer (thickness 0.3 μm) 38 made of n-GaAs is embedded in the p-type contact layer 39 so as to sandwich the central stripe portion from both sides.

Ohmic electrodes 41 and 42 are formed on the upper surface of the p-type contact layer 39 and the lower surface of the semiconductor substrate 40. The resonance direction of light is the direction perpendicular to the paper surface of FIG. 10A, and the cavity end surface of the semiconductor laser device is formed parallel to the paper surface of FIG. 10A.

As shown in FIG. 10B, n-type and p-type
The distribution of the Al composition ratio x of the mold carrier block layers 33 and 35 shows a trapezoidal shape, and the inner flat portion has x = 0.4 and the thickness is 2
00Å, x = 0.1 at the joint surface with the adjacent layer, and the region where the Al composition ratio decreases along the layer thickness direction has a thickness of 50Å. Therefore, the n-type and p-type carrier block layers 33, 3
The distribution shape of the forbidden band width of 5 also has a shape similar to a trapezoid. With this structure, the height of the potential barrier generated at the junction interface between the n-type and p-type carrier block layers 33 and 35 can be reduced, holes easily move in the valence band, and the injection efficiency into the active layer 34 is improved. To be done.

FIG. 11 is a graph showing the current-voltage characteristics of the semiconductor laser device. The broken line in FIG. 11 corresponds to the second embodiment shown in FIG. The solid line in FIG. 11 is Comparative Example 2, and the distribution of the Al composition ratio x of the n-type and p-type carrier block layers 33 and 35 is x = 0.4 in the inner flat portion and the thickness is 250 Å. It is a rectangular type with x = 0.1 on the surface.

Both Example 2 and Comparative Example 2 in FIG.
Cavity length 900μm, current injection stripe width 50μ
m, the optical coating has a common condition that the front surface has a reflectance of 10% and the rear surface has a reflectance of 96%. The n-type and p-type carrier block layers of Comparative Example 2 have a thickness of 250Å, and the Al composition ratio is uniform.

It can be seen from the graph of FIG. 11 that the driving voltage in Example 2 is reduced by about 10% as compared with Comparative Example 2.

In each of the above embodiments, the distribution of the forbidden band width of the p-type carrier block layer 35 is changed in the layer thickness direction,
An example in which the n-type carrier block layer 33 is constant and an example in which the forbidden band width distributions of both carrier block layers 33 and 35 are changed in the layer thickness direction are shown. However, the present invention is applied only to the n-type carrier block layer 33. It is also possible to apply.

In each of the embodiments, an example of using a ternary semiconductor material such as AlGaAs or InGaAs is shown, but the present invention is AlGaInP or GaInAsP.
The same can be applied to a quaternary semiconductor material such as a system.

[0045]

As described in detail above, according to the present invention, by forming a region in the carrier block layer in which the forbidden band width decreases along the layer thickness direction from the inside of the layer toward the bonding surface, the carrier block layer is formed. The height of the spike-shaped potential barrier generated at the hetero interface can be suppressed to a low level. Therefore, the carriers easily move into the active layer. As a result, the driving voltage of the semiconductor laser can be reduced, and excess heat generation can be suppressed, so that a highly reliable semiconductor laser can be obtained.

[Brief description of drawings]

[Figure 1] p-type semiconductor with forbidden band width of Eg1 and forbidden band width of Eg2
2A is an energy band diagram of a heterojunction with a p-type semiconductor of FIG. 1A, FIG. 1A is a state before joining, FIG. 1B is a state where both are directly joined, and FIG. 1C is a forbidden state along the layer thickness direction. It is in a state of being joined by providing a region where the band width changes.

FIG. 2 is a band diagram near a p-type carrier block layer of a PSCH semiconductor laser.

FIG. 3 is a distribution diagram schematically showing an Al composition ratio of a PSCH semiconductor laser.

FIG. 4 is a distribution chart showing an example of an Al composition ratio of a carrier block layer according to the present invention.

FIG. 5 is a distribution diagram showing another example of the Al composition ratio of the carrier block layer according to the present invention.

FIG. 6 is an explanatory diagram showing the carrier block layer thickness dependence of electron tunneling probability.

7 (a) is a sectional view showing an embodiment of the present invention, and FIG. 7 (b) is an Al of the p-type carrier block layer 35.
It is a distribution diagram showing a composition ratio.

FIG. 8 is a graph showing current-voltage characteristics of a semiconductor laser device.

9A and 9B are distribution diagrams of the Al composition ratio of the p-type carrier block layer, FIG. 9A being the example of FIG. 7 and FIG. 9B being the comparative example.

10A is a sectional view showing a second embodiment of the present invention, and FIG. 10B is a distribution diagram showing an Al composition ratio of the p-type carrier block layer 35.

FIG. 11 is a graph showing current-voltage characteristics of a semiconductor laser device.

12 (a) is a cross-sectional view showing an example of a semiconductor laser having a carrier block layer, and FIG. 12 (b).
Is a distribution diagram of the forbidden band width corresponding to each layer, and FIG. 12C is a distribution diagram of the refractive index corresponding to each layer.

13 (a) is an energy band diagram of a PSCH semiconductor laser, FIG. 13 (b) is an enlarged view near the n-type carrier block layer, and FIG. 13 (c) is an enlarged view near the p-type carrier block layer. It is a figure.

[Explanation of symbols]

 31 second n-type clad layer 32 first n-type clad layer 33 n-type carrier block layer 34 active layer 35 p-type carrier block layer 36 first p-type clad layer 37 second p-type clad layer 38 current confinement layer 39 p-type contact layer 40 semiconductor Substrate 41, 42 Ohmic electrode

Claims (4)

[Claims] 1. A clad layer is provided on both sides of an active layer, and a carrier block layer having a forbidden band width equal to or greater than a forbidden band width of the active layer and the clad layer is provided in proximity to the active layer. A semiconductor laser device, wherein in the block layer, a region in which the forbidden band width is reduced is formed along the layer thickness direction from the inside of the layer toward the bonding surface with the adjacent layer. 2. The region where the forbidden band width of the carrier block layer is maximum is at least 4 of the carrier tunnel length.
2. The semiconductor laser device according to claim 1, which has a double thickness. 3. The semiconductor laser device according to claim 1, wherein the forbidden band width at the junction surface of the carrier block layer is equal to or larger than the forbidden band width of an adjacent layer adjacent to the carrier block layer. 4. The n-type clad layer and the p-type clad layer each include a first clad layer and a second clad layer in the order of being closer to the active layer, where π is a circular constant, λ is an oscillation wavelength, and the first clad layer is The maximum refractive index of N1 is N1, the effective thickness between the second cladding layers is d1, the refractive index of the second cladding layer is N2, and V = (π · d1 / λ) · (N1 ² −N2 ² ) ^0.5 is defined. The semiconductor laser according to claim 1, 2 or 3, wherein V> π / 3.