JPH10154829A - Method of growing p-type nitride semiconductor and nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the light emitting effect and the light receiving efficiency of various kinds of devices using a P-type nitride semiconductor, by doping P-type impurities and oxygen simultaneously into the nitride semiconductor. SOLUTION: The conventional nitride semiconductor, on which P-type impurities only are doped, and the nitride semiconductor, on which P-type impurities and oxygen are simultaneously doped, are changed to low resistance P-type by annealing, and the comparison of this change is indicated in the diagram. A GaN buffer layer is grown on a sapphire substrate, and the recitatives of GaN (conventional) obtained by doping Mg thereon and the receptivity of GaN (this invention) obtained by doping Mg and O are plotted in the diagram as functions of the temperature. The resistivity of this invention is decreased by almost two orders of magnetic when compared with the conventional one. When the resistivity decreases by two orders of magnitude the contact resistance of the ohmic electrode formed don the P-type layer is also decreases, and the Vf of the nitride semiconductor element can be lowered sharply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a p-type nitride semiconductor (In _x Al _Y Ga) constituting a nitride semiconductor element applied to light emitting devices such as LEDs and LDs, light receiving devices such as solar cells and optical sensors. _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦
The present invention relates to the growth method 1) and a nitride semiconductor device using the growth method.

[0002]

2. Description of the Related Art A nitride semiconductor is a semiconductor material having a large number of lattice defects, and furthermore, it is known that nitrogen vacancies formed in a crystal in a non-doped (non-doped) state show n-type conductivity. Have been. Therefore, even if a p-type impurity is doped into a nitride semiconductor, i (insulate) having a high resistance is obtained.
r) It was a material that was difficult to obtain a p-type crystal with low resistance only in the form.

[0003] However, in 1983, Saparin et al.
By subjecting an i-type GaN layer doped with Zn to electron beam irradiation at a sample temperature of 300 K within a range not exceeding 20 keV and 200 A / cm ² , the photoluminescence (PL) intensity of Zn-doped GaN is improved. (Vestnik Moskovskogo Universiteta. Fizika, Vo
l.38, No.3, pp 56-59,1983). Also, JP-A-63-23
No. 9989 discloses an electron beam irradiation processing technique similar to the above-mentioned technique. Thereafter, Japanese Patent Application Laid-Open No. 2-257679 discloses that the GaN doped with Mg is subjected to an electron beam irradiation treatment to improve the PL intensity. An increase in PL intensity indicates that the resistivity of the portion irradiated with the electron beam is reduced, and the i-type is closer to the p-type. If these electron beam irradiation techniques are explained using Mg-doped GaN as an example, Mg-doped GaN immediately after growth does not contain Mg at the Ga site and is located at an interstitial position. For this reason, Mg does not work as an acceptor, and Mg-doped GaN shows high resistance. This i-type G
By irradiating aN with an electron beam, Mg moves with the energy of the electron beam to enter the Ga site, and Mg acts as an acceptor to exhibit low resistance.

On the other hand, apart from electron beam irradiation, the present applicant disclosed in Japanese Patent Application Laid-Open No. 5-183189 that annealing of a nitride semiconductor doped with a p-type impurity
The technique to make the mold is shown. This technology removes hydrogen by annealing from Mg-doped GaN, which is mixed with Mg and has a high resistance by being combined with Mg, and allows Mg to act as a normal acceptor, thereby achieving low-resistance. This is a technique to obtain p-type. Since this technology was announced, p-type nitride semiconductors have been studied by various research institutions. For example, JP-A-8-32113 discloses a technique for lowering the cooling rate, JP-A-8-51235 discloses a technique for simultaneously performing electrode annealing and p-annealing, and JP-A-8-8460.
Discloses an annealing technique in which an n-layer is placed on a p-layer.

Further, it has been shown that a p-type with a high carrier concentration can be obtained by growing GaN doped with Be and oxygen on a GaAs substrate by MBE (Appl. Phys. Lett. 69 (Appl. 18), 28 Oct 1996 pp2707-270
9).

[0006]

However, even if a p-type layer is obtained by annealing, the carrier concentration is only 1 × 10 ¹⁸ / cm ³ or less, and a p-type layer having a higher carrier concentration is not used. It has been demanded. When a p-type layer having a high carrier concentration is obtained, an LED using a nitride semiconductor,
The Vf of the LD or the like is extremely reduced, and the LD generates less heat, so that continuous oscillation is possible. Accordingly, it is an object of the present invention to improve the light emitting efficiency and light receiving efficiency of various devices using the p-type nitride semiconductor by providing a growth method capable of obtaining a p-type nitride semiconductor having a high carrier concentration. To make it happen.

[0007]

According to the present invention, there is provided a method for growing a p-type nitride semiconductor, comprising the steps of: growing a nitride semiconductor by metalorganic vapor phase epitaxy; It is characterized by being doped simultaneously with oxygen. In the present invention, the p-type impurity is defined as 2A of the periodic table.
And at least one element selected from Group 2B. In the method of the present invention, a technique of simultaneously doping a plurality of p-type impurities is also included in the scope of the present invention. Most preferably, the p-type impurity is Mg.

Further, the growth method of the present invention is characterized in that after growing a nitride semiconductor containing a p-type impurity and oxygen, hydrogen contained in the nitride semiconductor layer is removed. Note that removing hydrogen contained in the nitride semiconductor layer does not mean removing all hydrogen, but also includes removing a small amount of hydrogen within the scope of the present invention.

In the growth method of the present invention, the means for removing hydrogen is annealing (heat treatment).
Lamp annealing, plasma annealing,
Means such as annealing in a reaction vessel and annealing at a reduced cooling rate are also included. In addition to annealing, there is also an electron beam irradiation technique, but practically and industrially, annealing is most preferable. In the case of annealing, the annealing temperature is most preferably 300 ° C. or more, and the annealing is performed in an atmosphere containing no hydrogen. This is because if performed in an atmosphere containing hydrogen, H is reoccluded.

Further, the present invention is characterized in that the hole carrier concentration of the nitride semiconductor is adjusted by adjusting the doping amount of oxygen. When the hole carrier concentration can be adjusted, p-,
A nitride semiconductor such as p + can be easily formed.

A nitride semiconductor device according to the present invention has a nitride semiconductor having an n-type nitride semiconductor layer, an active layer made of a nitride semiconductor containing indium, a p-type nitride semiconductor layer, and a p-electrode layer in this order. The device is characterized in that at least one p-type nitride semiconductor layer doped with p-type impurities and oxygen is provided between the active layer and the p-electrode layer.

Further, in the device of the present invention, the doping amount of oxygen in the p-type nitride semiconductor layer doped with p-type impurities and oxygen is 0.1% or more with respect to the doping amount of the p-type impurities. It is characterized by being within a range not exceeding the doping amount of the p-type impurity.

As described above, the p-type impurity is the second in the periodic table.
It is at least one element selected from the group A and the group 2B, and among them, Mg, Ba, Ca,
Elements that are almost harmless to the environment and are easy to handle, such as Sr and Zn, are preferable, and among them, Mg is particularly preferable because a p-type element having the highest carrier concentration can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a conventional p-type impurity-doped nitride semiconductor, a p-type impurity of the present invention, and a nitride semiconductor doped simultaneously with oxygen. It is a figure which shows that it changes to. This means that a GaN buffer layer is grown on a sapphire substrate by 200 angstroms, and M
FIG. 3 is a diagram showing the resistivity of GaN doped with g (conventional) and GaN doped with Mg and O (invention), respectively, as a function of temperature.

As shown in this figure, according to the present invention, the resistivity is reduced by nearly two orders of magnitude as compared with the prior art. When the resistivity is reduced by two digits, the contact resistance of the ohmic electrode formed on the p-type layer is further reduced, so that the Vf of the device can be significantly reduced. Further, in the related art, the resistivity starts decreasing around 400 ° C., whereas in the present invention, the resistivity starts decreasing around 300 ° C. The fact that the annealing temperature is lowered means that the p-type can be obtained in a shorter time than before,
Further, there is an effect that the options of the annealing apparatus are widened and almost any means can be used as long as the apparatus can perform the heat treatment. FIG. 1 shows Mg-doped GaN.
However, other nitride semiconductors, for example, a nitride semiconductor containing Al such as AlGaN have the same tendency. Further, it was confirmed that the same tendency was observed for other p-type impurities, such as Zn, Ba, Be, etc., but it was confirmed that Mg had the most remarkable effect in combination with oxygen.

The p-type nitride semiconductor of the present invention (hereinafter, the nitride semiconductor may be referred to as GaN in the description of the present invention) is grown by metal organic chemical vapor deposition. In the metal organic chemical vapor deposition method, a compound containing H such as ammonia or hydrazine is used as a source gas as an N source. These hydrogen compounds are decomposed in the reaction vessel during or after the growth of GaN, and GaN is inevitably mixed with p-type impurities.
Incorporated in the layer. Many of the doped p-type impurities do not enter Ga sites in the GaN crystal,
And N. Moreover, the p-type impurities are inactivated by bonding to H doped in the crystal. Therefore, in the present invention, by doping oxygen simultaneously with the p-type impurity, the p-type impurity which has not entered the Ga site is replaced by oxygen, and the p-type impurity easily enters the Ga site. Moreover, since oxygen is not implanted later by ion implantation or the like, but is doped simultaneously with the p-type impurity, oxygen easily enters the intermediate position between Ga and N or the N position, and the p-type impurity is more easily introduced into the Ga site. Easy to enter. That is, before removing hydrogen, G
Since the amount of the p-type impurity entering the a-site can be increased, the amount of the p-type impurity acting as an acceptor increases after hydrogen bonded to the p-type impurity is removed, so that the carrier concentration is significantly improved.

FIG. 2 is a diagram showing the relationship between the O concentration and the hole carrier concentration of a p-type nitride semiconductor layer which is doped with O and Mg and has a low resistance by annealing. This is because when growing GaN doped with Mg and O by MOCVD, the gas flow rate of the O source is changed and Mg is reduced to 1 ×.
A GaN layer doped with various concentrations of O is formed on a GaN layer doped with 10 ²⁰ / cm ³ , and the relationship between the carrier concentration of the GaN layer and the O concentration is shown.

As shown in FIG. 2, p-type GaN is, Mg and 1 × 10 ²⁰ / cm ³ even despite the doping, carrier concentration no more than ³ × 10 ¹⁷ / cm 3. This shows how few p-type impurities are acting as normal acceptors. However, O is 1 × 10
By doping in the vicinity of ¹⁷ / cm ³ (0.1% with respect to Mg), the carrier concentration is increased by two orders of magnitude and 5 × 10 ¹⁸
/ Cm ³ to about 8 × 10 ¹⁹ / cm ³ , which is almost constant. Then, when the amount becomes equal to the amount of the doped p-type impurity, the donor and the acceptor cancel each other. When the O concentration exceeds the p-type impurity, the donor and the acceptor become n-type. Value. Therefore, O for p-type impurities
Is preferably 0.1% or more and does not exceed the p impurity amount, more preferably 0.5% or more, most preferably 5% or more and 80% or less. When the p-type impurity and O are simultaneously doped as described above, the carrier concentration is improved by two orders of magnitude, but it is still difficult to obtain a carrier concentration equal to the amount of the doped p-type impurity. This is Ga
It is inferred that many p-type impurities which have not entered the site still remain and that many lattice defects exist.

In the present invention, the carrier concentration of the p-type layer can be adjusted by O by simultaneously doping the p-type impurity and O. That is, in the conventional case, the p-type impurity concentration and
Although the carrier concentration is adjusted only by annealing, the carrier concentration can be easily adjusted by newly doping O and changing the doping amount. For this reason, the p-type layer above the active layer is formed, for example, by p-type with a low carrier concentration.
When a layer and a p + layer having a higher carrier concentration are stacked in this order, and a p-electrode is formed on the p + layer having a higher carrier concentration, the carrier injection efficiency is improved and the output is improved.

The nitride semiconductor doped with p-type impurities and O at the same time is preferably grown after growing an active layer made of a nitride semiconductor containing indium.
The active layer containing In, particularly InGaN, has a crystalline property that is softer than other Al-containing nitride semiconductors,
Or it is elastic. Therefore, InGaN functions as a buffer layer. Therefore, the nitride semiconductor grown on InGaN has good crystal properties, and is likely to be p-type with a high carrier concentration by doping with a p-type dopant and O.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a nitride semiconductor device using the method of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of a nitride semiconductor light emitting device according to one embodiment of the present invention, and specifically shows the structure of an LED.

The substrate 1 made of sapphire (C-plane) is set in a reaction vessel, and after sufficiently replacing the inside of the vessel with hydrogen, the temperature of the substrate is increased to 1050 ° C. while flowing hydrogen to clean the substrate. . Another sapphire C face substrate 1, a sapphire having the principal R-plane, A plane, other, including other insulating substrate such as spinel _{(MgA1 2 O 4), SiC} (6H, 4H, and 3C ), ZnS, Zn
A semiconductor substrate of O, GaAs, GaN, or the like can also be used.

Subsequently, the temperature is lowered to 510 ° C., and a buffer layer 2 made of GaN is formed on the substrate 1 to a thickness of about 200 Å using hydrogen as a carrier gas, ammonia and TMG (trimethylgallium) as source gases. Let it grow. The buffer layer is made of AlN, GaN, AlGaN, etc.
At a temperature of 900 ° C. or less, the film can be formed with a film thickness of several tens to several hundreds of angstroms. This buffer layer is formed in order to alleviate the lattice constant mismatch between the substrate and the nitride semiconductor, but may be omitted depending on the growth method of the nitride semiconductor, the type of the substrate, and the like.

After the growth of the buffer layer 2, only TMG is stopped.
Raise the temperature to 1030 ° C. When the temperature reaches 1030 ° C., a 5 μm-thick Si-doped n-type GaN layer doped with 8 × 10 ¹⁸ / cm ^{3 of} Si is used as the n-type contact layer 3 using TMG, ammonia gas, and silane gas as the source gas. Grow in thickness. This layer also
Not only as a contact layer to form an electrode,
It also acts as an n-type clad layer that confines carriers. n-type contact layer 3 is _{In X Al Y Ga 1-X-} Y N (0
≦ X, 0 ≦ Y, X + Y ≦ 1), and especially G
By being composed of aN, InGaN, and among them, n-type impurities, particularly GaN doped with Si or Ge,
An n-type layer having a high carrier concentration is obtained, and a favorable ohmic contact with the n-electrode is obtained. As the material for the n-electrode, a metal or alloy such as Al, Ti, W, Cu, Zn, Sn, and In can be used to obtain an ohmic.

Next, the temperature was set to 800 ° C., the carrier gas was switched to nitrogen, and TMG, TMI (trimethylindium), and ammonia were used as source gases, and a single quantum well structure (SQW: Single Angstrom) having a thickness of 30 Å was used. Q
An active layer 4 of In0.2Ga0.8N (uantum Well) is grown. Active layer 4 made of nitride semiconductor containing In
Represents a single quantum well structure or a multiple quantum well structure (MQ
W: Multi Quantum Well). When the active layer has a quantum well structure such as SQW or MQW, it is desirable to have a well layer made of a nitride semiconductor containing at least In.
The film thickness is adjusted to 0 angstrom or less, more preferably 50 angstrom or less. In the case of MQW, the barrier layer is composed of a nitride semiconductor layer having a larger band gap energy than the well layer, and the thickness is adjusted to 150 Å or less, more preferably 100 Å or less. In the case of MQW, the barrier layer does not need to be particularly a nitride semiconductor containing In, but is preferably a nitride semiconductor having a larger band gap than the well layer containing In. Because, the nitride semiconductor containing In is AlGa
The growth temperature is lower than that of N or GaN. That is, the decomposition temperature is A
lower than lGaN. When trying to stack a barrier layer made of AlGaN grown at a high temperature on a well layer made of InGaN grown at a low temperature, not a little
Decomposes. Therefore, a well layer made of InGaN and In
If a barrier layer made of GaN is stacked, the growth can be performed at the same temperature, and the InGaN layer grown earlier does not decompose, so that a high-output light-emitting element can be realized.

After the growth of the active layer 4, the temperature is raised to 1050 ° C., and TMG, TMA (trimethylaluminum), ammonia as the source gas, oxygen gas as the impurity gas, and Cp2Mg (cyclopentadienyl magnesium) gas as the p-type impurity gas. At the same time, 5 × 1 O was used in a nitrogen carrier.
A p-type cladding layer 5 made of p-type Al0.2Ga0.8N having a low carrier concentration doped with 0 ¹⁷ / cm ³ and Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.5 μm. The p-type layer in contact with the active layer is formed of a nitride semiconductor layer containing Al, preferably A
When l _X Ga _{1 -X} N (0 <X ≦ 1), the light emission output is improved. The p-type cladding layer 5 is preferably grown to a thickness of 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less. 1
If the thickness is smaller than 00 Å, it does not easily act as a cladding layer, and if the thickness is larger than 2 μm, cracks tend to be formed in the crystal. When growing a nitride semiconductor doped with a p-type impurity and oxygen as described above, it goes without saying that an inert gas such as nitrogen or argon is used as a carrier gas. For doping oxygen, oxygen may be intentionally mixed into the raw material gas. However, for doping quantitatively, the doping is performed while controlling the flow rate by an MFC (mass flow controller) as an impurity gas separately from the raw material gas. It is desirable to do.

Subsequently, the temperature was maintained at 1030 ° C.
Stop the gas, increase the flow rate of silane gas,
The p-type contact layer 5 made of p + -type GaN having a high carrier concentration doped with 0 ²⁰ / cm ³ and O at 1 × 10 ¹⁹ / cm ^{3 has a} thickness of 0.
It is grown to a thickness of 5 μm. The p-type contact layer 5 is a p-type In _X Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1)
, But particularly preferably In _x Ga
_1-X N (0 ≦ X ≦ 1). 1 × 10 ¹⁹ as in the present invention
If the p-type layer having a carrier concentration of / cm ³ or more is used as the contact layer, the contact resistance with the ohmic electrode material decreases. Examples of the electrode material that can obtain a preferable ohmic with the p-type layer include Cr, Ni, Au, Pd, and Ti.

After the reaction is completed, the temperature is lowered to 600 ° C., the wafer is annealed in a reaction vessel in a nitrogen atmosphere, and a part of hydrogen contained in the p-type cladding layer and the p-type contact layer is removed. The resistance of the p-type layer is further reduced.

After annealing, the wafer is taken out of the reaction vessel and, as shown in FIG. 3, is etched from the uppermost p-type contact layer 6 side by an RIE apparatus to form an n-type contact layer 3 on which an n-electrode 8 is to be formed. Expose the surface.

Next, Ni and Au are formed on the p-type contact layer 12.
On the other hand, an n-electrode 8 made of Ti and Al is formed on the exposed n-type contact 3.

As described above, the wafer on which the p-electrode 7 and the n-electrode 8 are formed is transferred to a polishing apparatus, and the sapphire substrate 1 on which the nitride semiconductor is not formed is wrapped using a diamond abrasive. The thickness of the substrate is set to 90 μm, and the sapphire substrate side is scribed to form LED chips of 350 μm square. When this LED chip was caused to emit light with a forward current (If) of 20 mA, the conventional LED in which the p-layer was not doped with Si had a (forward voltage) Vf of 3.5.
V, whereas the LED of the present invention was 2.8 V and 0.8 V.
7V also dropped. Further, at an emission wavelength of 450 nm, the output was improved 1.5 times as compared with the conventional LED.

Example 2 An LED element was fabricated in the same manner as in Example 1 except that O was doped at 1 × 10 ¹⁹ / cm ³ when growing the p-type cladding layer 5.
f is almost the same as that of the first embodiment, and the output is
It was 1.3 times that of ED.

[0033]

According to the present invention, by doping oxygen in addition to the p-type impurity, the number of holes injected into the active layer is essentially increased, and the luminous efficiency is improved. Since the carrier concentration of the p layer increases, a favorable ohmic with the p layer can be obtained. On such a p layer, p
When the electrodes are formed, the contact resistance can be further reduced, and Vf can be greatly reduced. Needless to say, the technology of the present invention can be applied to not only light-emitting devices such as LEDs and LDs but also all electronic devices using nitride semiconductors such as transistors, FETs and MOSs.

When the Vf of the nitride semiconductor device decreases, it is very convenient for a full-color display using a nitride semiconductor. That is, in the current full-color display, the red LED is made of a GaAs-based or AlInGaP-based semiconductor material, and the green LED and the blue LED are made of a nitride semiconductor. GaAs-based and AlInGaP-based red LEDs have a Vf of the order of 1 V, whereas nitride semiconductor LEDs conventionally have a Vf of 3.5 V. Therefore, blue and green LEDs have been used with a reduced current so as not to generate much heat to the LEDs. On the other hand, red LEDs have been used under severe conditions such as increasing the number of LEDs or using them at full specification values in order to balance luminance with green and blue LEDs. Therefore, red LE
D has a drawback that its reliability due to heat generation is lower than that of the blue LED and the green LED. However, according to the present invention, since the Vf of the green and blue LEDs is reduced, the overall heat generation can be reduced. Therefore, realizing the full-color display of the present invention improves the overall reliability. Furthermore, even when used under severe conditions such as a signal lamp, when Vf decreases, the amount of heat generation also decreases, and reliability is greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a comparison between the annealing temperature and the resistivity of a p-type nitride semiconductor of the present invention doped with O and a p-type impurity and a conventional p-type nitride semiconductor.

FIG. 2 shows a nitride semiconductor layer in the method of the present invention.
FIG. 5 is a graph showing a relationship between a concentration and a hole carrier concentration.

FIG. 3 is a schematic sectional view showing the structure of an LED element according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 3 ... n-type contact layer 4 ... Active layer 5 ... p-type cladding layer 6 ... p-type contact layer 7 ... p-electrode 8 ...・ N electrode

Claims (7)

[Claims] 1. A method for growing a nitride semiconductor by metalorganic vapor phase epitaxy, wherein a p-type impurity and oxygen are simultaneously doped during the growth of the nitride semiconductor. Growth method. 2. The method for growing a p-type nitride semiconductor according to claim 1, wherein after growing the nitride semiconductor, hydrogen contained in the nitride semiconductor layer is removed. 3. The method for growing a p-type nitride semiconductor according to claim 1, wherein said means for removing hydrogen is annealing. 4. The method of growing a p-type nitride semiconductor according to claim 2, wherein said annealing temperature is 300 ° C. or higher. 5. The p-type nitride according to claim 1, wherein the hole carrier concentration of the nitride semiconductor is adjusted by adjusting the doping amount of the oxygen. Method of growing semiconductors. 6. A nitride semiconductor device having an n-type nitride semiconductor layer, an active layer made of a nitride semiconductor containing indium, a p-type nitride semiconductor layer, and a p-electrode layer in this order. And at least one p-type nitride semiconductor layer doped with a p-type impurity and oxygen between the p-type electrode layer and the p-type electrode layer. 7. The p-type nitride semiconductor layer doped with p-type impurities and oxygen has an oxygen doping amount of 0.1% or more with respect to the p-type impurity doping amount, and 7. The nitride semiconductor device according to claim 6, wherein the amount does not exceed the doping amount.