JPH10173227A - GaN element - Google Patents

Abstract

(57) [Problem] To provide a GaN-based device in which steepness of composition at an interface between a quantum well layer having a superlattice structure and a barrier layer is secured. SOLUTION: A quantum well layer and a barrier layer are formed by an MOVPE method, and a semiconductor layer thereon and a p-type layer in a light emitting element are formed by an MBE method. According to the MBE method, the semiconductor layer can be grown at a temperature lower than the temperature at which the quantum well layer and the barrier layer are grown by the MOVPE method. If the growth temperature of the semiconductor layer formed on the quantum well layer and the barrier layer is lower than the growth temperature of the quantum well layer and the barrier layer, even if such a temperature history is received by the quantum well layer and the barrier layer, The steepness of the difference in composition at the interface of is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a GaN-based device. The present invention is applied to, for example, a GaN-based light emitting device having a light emitting layer having a super lattice structure.

[0002]

2. Description of the Related Art Conventionally, a light emitting device having a light emitting layer of a superlattice structure has a buffer layer, an n-G
The configuration was such that an aN-based layer (n ⁺ contact layer, n-cladding layer), a light emitting layer having a superlattice structure, and a p-GaN-based layer (p-cladding layer, p ⁺ contact layer) were sequentially laminated. Each semiconductor layer is formed by metal organic compound vapor deposition (hereinafter referred to as “MOVPE”).
It was grown by.

[0003]

The light emitting layer having the superlattice structure has a structure in which a quantum well layer and a barrier layer are repeatedly laminated, and the quantized carriers are confined in the quantum well layer. To ensure the confinement of carriers, steepness is required between the quantum well layer and the barrier layer. That is,
The interface between the quantum well layer and the barrier layer is required to have sharp composition.

[0004] According to the MOVPE method, the quantum well layer and the barrier layer can be grown while ensuring the sharpness of the composition at the interface. However, according to the MOVPE method, p
In order to grow a GaN-based layer, a temperature higher than the growth temperature of the quantum well layer and the barrier layer is required. For example, while the growth temperature of the light emitting layer is 700 to 900 ° C., p
The growth temperature of the -GaN-based layer is 1000 to 1100C. The reason why the growth temperature of the latter is higher than the growth temperature of the former is to obtain a sufficient hole concentration in the p-GaN-based layer.

[0005] Initially, even when the light emitting layer has a superlattice structure having a sharp difference in composition at the interface between the quantum well layer and the barrier layer, the temperature is higher than the growth temperature when growing a p-GaN-based layer. When exposed to the temperature, diffusion of atoms occurs at the interface between the quantum well layer and the barrier layer, and the sharpness of the difference in composition at the interface may be impaired. Such a loss of steepness causes a decrease in luminous efficiency, which is not preferable.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. That is, an element formed of a GaN-based compound semiconductor, a superlattice structure layer having a first layer in which carriers are confined and a barrier layer sandwiching the first layer; Another semiconductor layer to be formed, wherein the superlattice structure layer is a layer formed by MOVPE,
The other semiconductor layer is formed by a molecular beam epitaxy method (hereinafter referred to as “M”).
BE method).

In the above, the first layer in which carriers are confined can be a linear layer or a box-shaped layer having one or two or more two-dimensional spreads, and constitutes a quantum wire and a quantum box, respectively. I do.

[0008] Such a superlattice structure layer becomes a light emitting element structure by sandwiching it with an n clad layer and a p clad layer.

[0009]

The MBE method can grow at a lower temperature than the MOVPE method. Therefore, the superlattice structure layer is
After being formed by the PE method, another semiconductor layer can be formed thereon by MBE at a temperature lower than the growth temperature of the superlattice structure layer. If the growth temperature of the semiconductor layer formed on the quantum well layer and the barrier layer is lower than the growth temperature of the quantum well layer and the barrier layer, even if such a temperature history is received by the quantum well layer and the barrier layer, The steepness of the difference in composition at the interface of is maintained. Thus, when such a superlattice structure is used as a light emitting layer of a light emitting diode, the luminous efficiency is improved, the half width of the spectrum of the output light is reduced, and the color purity is improved. When such a superlattice structure is used as a light emitting layer of a laser diode,
The value of the oscillation threshold current becomes small, and high-output laser oscillation with a small current can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples. The device of this embodiment is a light emitting diode. FIG. 1 shows a cross-sectional view of the light emitting diode 20 of the embodiment.

A buffer layer 2 made of AlN having a thickness of 20 nm is formed on an a-plane of a sapphire substrate 1 having a thickness of 100 μm. The buffer layer 2 has a thickness of 20 to 50 nm.
And the growth temperature of the film is 400 ° C.

On the buffer layer 2, an n-GaN-based layer
Formed in layers. This n-GaN-based layer is composed of n ⁺ doped with 2.5 μm thick silicon at a high concentration from the lower side.
-GaN layer 3 (n-contact layer) and n-GaN layer 4 (n-cladding layer) doped with 0.5 μm thick silicon
It is composed of These n-GaN-based layers are made of Al _X In _Y G
a _1-XYN (including X = 0, Y = 0, and X = Y = 0).

A light emitting layer 5 having a super lattice structure is formed on the n clad layer 4. The light emitting layer 5 has a barrier layer 5a made of GaN not doped with intentional impurities of 3.5 nm and a quantum layer made of In _0.15 Ga _0.85 N not doped with intentional impurities of 3.5 nm in thickness. In this configuration, the well layers 5b are repeatedly laminated. In this embodiment, the number of repetitions is 5. And the barrier layer 5 formed on the uppermost
c consists of 3.5 nm thick undoped GaN without intentional impurities.

In the above, the number of repetitions of the barrier layer 5a and the quantum well layer 5b is not particularly limited. Barrier layer 5a, 5c is _{In Y1 Ga 1-Y1 N (} Y1 ≧ 0) made of a compound semiconductor, quantum well layer 5b is In _Y2 Ga _1-Y2 N
(Y2> Y1 and Y2> 0).

The barrier layers 5a and 5c and the quantum well layer 5b can be doped with intentional impurities.

On the light emitting layer 5, two p-cladding layers (other semiconductor layers) having a band gap wider than that of the barrier layer are formed. This p-cladding layer is formed from below with 100 nm thick magnesium-doped p-Al _0.15
It comprises a Ga _0.85 N layer 6 and a 200 nm thick p-GaN layer 7 doped with magnesium. This p-cladding layer is made of Al _A In _B Ga _{1 -AB} N (A = 0, B = 0, A =
B = 0 (including B = 0). This p-cladding layer may be composed of one layer.

On the p-GaN layer 7, a thickness of 25.0 nm
A GaN layer 8 (p-contact layer) doped with magnesium at a higher concentration than the p-GaN layer 7 is formed.
This layer is provided to reduce the contact resistance to the electrode.

The n-electrode 9 is made of Al, Ti or an alloy containing them. Reference numeral 10 denotes a light-transmitting electrode which is formed on the p-contact layer 8 over substantially the entire surface thereof. The pad electrode 11 is formed on the translucent electrode 10. Au, P is used as a material for forming the translucent electrode 10 and the pad electrode 11.
t, Pd, Ni, or an alloy containing them.

Next, a method for manufacturing the light emitting diode 20 of the embodiment will be described. The n-GaN-based layers 3 and 4 and the light-emitting layer 5 of the light-emitting diode 20 are formed by a MOVPE method according to a standard method. In this growth method, ammonia gas and 3
An alkyl compound gas of a group element, for example, trimethylgallium (TMG), trimethylaluminum (TMA) or trimethylindium (TMI) is supplied to a substrate heated to an appropriate temperature to cause a thermal decomposition reaction, thereby forming a desired crystal. Grow on the substrate. The flow rates and reaction times of the carrier gas, the ammonia gas, and the alkyl compound gas of the Group 3 element are appropriately adjusted according to the target crystal.

First, organic cleaning and heat treatment were performed.
The single crystal sapphire substrate 1 having the a-plane as a main surface is mounted on a susceptor 32 in a MOVPE apparatus 31 shown in FIG. Next, while flowing H ₂ into the reactor at normal pressure, the temperature was 1100 ° C.
Vapor-phase etches the sapphire substrate. Such MOV
The basic structure of the PE device 31 is well known. For example, see JP-A-63-188934. The susceptor 32 of the MOVPE device 31 of this embodiment is mounted on a transfer device 37. The reaction chamber communicates with a vacuum passage 35 opened and closed by a shutter 41.

Next, the temperature is lowered to 400 ° C.
₂ , NH ₃ and TMA are supplied to form an AlN buffer layer 2 on the substrate to a thickness of about 20 nm.

Next, the temperature is raised to 1100 ° C., H ₂ , silane, TMG, and NH ₃ are introduced to form the n-contact layer 3, and the silane flow rate is further reduced to form the n-cladding layer 4.

Subsequently, the temperature was maintained at 750 ° C., and N ₂ ,
A barrier layer 5a made of GaN having a thickness of 3.5 nm is formed by introducing TMG and NH ₃ . N ₂ , NH ₃ , TMG and T
A quantum well layer 5b made of In _0.15 Ga _0.85 N and having a thickness of 3.5 nm is formed by introducing MI. Repeat this,
As shown in the figure, five barrier layers 5a and five quantum well layers 5b are obtained.

An uppermost barrier layer 5c made of GaN is formed on the fifth-stage quantum well layer 5b.

After the light emitting layer 5 having the super lattice structure is formed in this manner, the shutter 4 of the manufacturing apparatus 30 (see FIG. 2) is used.
The susceptor 32 in the MOVPE device 31 is moved into the MBE device 31 by sequentially opening the devices 1 and 42 and operating the transfer device 37. And shutter 4
1 and 42 are sequentially closed to prepare for the MBE method. MBE
The basic structure of the device 33 is also well known. See, for example, JP-A-5-175124.

In the manufacturing apparatus 30 shown in FIG. 2, the vacuum passage 35 is connected to the reaction chamber of the MOVPE apparatus 31 and the MBE apparatus 33.
And the inside thereof is maintained at a predetermined degree of vacuum. Transfer device 37 is MOV
Reaction chamber of PE device 31, vacuum passage 35 and MBE device 3
3 and the susceptor 32 is connected to the MOVP
The transfer is performed between the E device 31 and the MBE device 33. Instead of the susceptor 32, the work itself held by the susceptor can be transferred. Reference numerals 41 and 43 in the figure denote shutters, which are a MOVPE device 31 and an MBE, respectively.
The device 33 is provided for the purpose of maintaining a predetermined degree of vacuum. That is, the shutters 41 and 43 are closed with the transfer device 37 stopped, and when the transfer device 37 is on, the shutters 4 are allowed to operate.
1, 43 open and close at a predetermined timing. The transfer device 37 and the shutters 41 and 43 are controlled by a control device (not shown).

FIG. 3 shows another manufacturing apparatus 40. The same members as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.
In the manufacturing apparatus 40, the transfer device 370 transfers the work. The vacuum passage 350 is provided with a room 50 for stacking works. Reference numeral 60 in the figure denotes a work stack. By stacking the work in this way, the difference between the processing speed of the MOVPE device 31 and the processing speed of the MBE device 33 can be absorbed, and a series of steps of the embodiment can be continuously executed. Reference numerals 51 and 5 in the figure
3 is the second for maintaining the degree of vacuum in the room 50 at a predetermined value.
Shutter. That is, the second shutters 51 and 53 and the shutters 41 and 43 are closed when the transfer device 370 is stopped. When the transfer device 370 is turned on, the second shutter 51 and the second shutter 51 are allowed to operate. , 53 and shutters 41, 43 open and close at a predetermined timing. Transfer device 370, shutter 4
1, 43, 51, and 53 are controlled by a control device (not shown).

The p-GaN based layers 6 to 8 are formed by performing the MBE method using the MBE apparatus 33 described above. In the MBE apparatus 33, the temperature of the susceptor 32 is maintained at 660 ° C., and the MBE method is performed, and p-Al _0.15 doped with magnesium having a growth rate of 200 nm / h and a film thickness of 100 nm is used.
A layer 6 made of Ga _0.85 N is formed. Then raise the temperature to 6
At 60 ° C., the supply of Al was stopped, and the growth rate was 20
A p-GaN layer 7 doped with magnesium at 0 nm / h and 200 nm in thickness is formed.

The p-cladding layers 6 and 7 have a hole concentration of 2 × 10 ¹⁸ / cm ³ , and have sufficient conductivity as an element in this state.

Continuing with the formation of the layer 7, while maintaining the temperature at 660 ° C., the supply of magnesium was increased to increase the growth rate of 200 nm / h and the p-contact layer 8 with a high concentration of 25 nm thick magnesium. To form This p
Hole concentration of contact layer 8 is ³ X 10 ¹⁸ / cm 3, has a sufficient conductivity as an element in this state.

As in the prior art, the p-GaN-based layers 6, 7 and 8
Was formed by the MOVPE method, these layers had high resistance in a state where the layers were grown (as-grown). Therefore, a separate step for lowering the resistance of these layers is required. For example, electron beams are irradiated (see Japanese Patent Application Laid-Open No. 3-218625). However, as in this example, the p-
Since the GaN-based layer has sufficient conductivity as an element, it does not require a step of reducing the resistance.

The growth temperature of the p-GaN based layer is MOVPE
The hole concentration and the steepness of the interface are not impaired even if the temperature is increased to about the same as the growth temperature of the light emitting layer in the method.

The semiconductor wafer thus formed is etched by a known method to obtain the semiconductor layer structure shown in FIG. Then, an n-electrode 9 is formed on the n-contact layer 3 by vapor deposition.
Evaporated on the contact layer 8 and further made of a gold pad electrode 1
1 is deposited.

The semiconductor wafer thus formed is cut into individual devices to obtain desired light emitting diodes 20.

The present invention is not limited to the description of the above-described embodiments and examples, and includes various modifications that can be made by those skilled in the art without departing from the scope of the claims. Needless to say, the present invention can be applied to a laser diode.

Hereinafter, the following items will be disclosed. (1) An element formed of a GaN-based compound semiconductor, comprising: a superlattice structure layer having a first layer in which carriers are confined; a barrier layer sandwiching the first layer; Comprising another semiconductor layer formed on the GaN
A GaN-based device, wherein the difference in composition at the interface between the first layer and the barrier layer is sharp.

(2) A superlattice structure layer having a first layer in which carriers are confined and a barrier layer sandwiching the first layer is formed at a first growth temperature by MOVPE, and thereafter,
A method for manufacturing a GaN-based device, comprising forming another semiconductor layer on the superlattice structure layer at a second growth temperature lower than the first growth temperature by MBE.

(3) A first cladding layer of the first conductivity type is formed by MOVPE, and a light emitting layer having a superlattice structure is formed on the first cladding layer by MOVPE at a first growth temperature. And forming a second conductivity type cladding layer on the light emitting layer by MBE at a second growth temperature lower than the first growth temperature. Device manufacturing method.

(4) The first for executing the MOVPE method
A second apparatus for performing the MBE method; a vacuum passage communicating with the reaction chamber of the first apparatus and the reaction chamber of the second apparatus and maintained at a predetermined vacuum degree; A transfer device for transferring a work or means for holding the work through the vacuum passage between the reaction chamber of the first apparatus and the reaction chamber of the second apparatus.

(5) A first shutter disposed between the reaction chamber of the first apparatus and the vacuum passage for opening and closing the communication between the first chamber and the vacuum passage, and a first shutter between the reaction chamber of the second apparatus and the vacuum passage. (4) The apparatus for manufacturing a GaN-based element according to (4), further including a second shutter disposed between the two to open and close communication between the two.

(6) A means for stacking the work or a means for holding the work is further provided (4) or (5).
3. The apparatus for manufacturing a GaN-based element according to item 1.

(7) The GaN-based device according to (6), wherein the transfer device transfers the work or the means for holding the work between the stack means and the MOVPE apparatus and between the stack means and the MBE apparatus. Manufacturing equipment. (8) The apparatus for manufacturing a GaN-based element according to (6) or (7), further comprising a third shutter disposed between the stacking means and the vacuum passage to open and close the communication between them.

[Brief description of the drawings]

FIG. 1 is a sectional view of a light emitting diode according to an embodiment of the present invention.

FIG. 2 shows a configuration of an apparatus for manufacturing a light emitting diode according to an embodiment of the present invention.

FIG. 3 shows the configuration of another apparatus for manufacturing a light emitting diode according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 4 n clad layer 5 Light emitting layer of super lattice structure 6, 7 p clad layer 9, 10, 11 electrode 20 light emitting diode 31 MOVPE device 33 MBE device

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masayoshi Koike 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Inside Toyoda Gosei Co., Ltd. (72) Inventor Isamu Akasaki 1-38-805, Joshin, Nishi-ku, Nagoya, Aichi Prefecture

Claims (2)

[Claims] 1. An element formed of a GaN-based compound semiconductor, comprising: a superlattice structure layer having a first layer for confining carriers and a barrier layer sandwiching the first layer; A further semiconductor layer formed on the GaN-based device, wherein the superlattice structure layer is formed by metal organic compound vapor phase epitaxy (MOVP).
A GaN-based device, wherein the GaN-based device is a layer formed by an E) method, and the other semiconductor layer is a layer formed by a molecular beam epitaxy (MBE) method. 2. A first layer of the superlattice structure layer is a quantum well layer, the other semiconductor layer is a p-type cladding layer, and an n-type cladding layer below the superlattice structure layer. The GaN-based device according to claim 1, further comprising a light-emitting device.