JPH04278523A - Semiconductor material having si-doped gainp buffer layer - Google Patents

Abstract

PURPOSE:To obtain semiconductor material wherein propagation of a particular crosshatched pattern and dislocation caused by a GaAsP substrate is prevented. CONSTITUTION:An Si-doped GaInP layer 2 and a GaInP layer 3 are formed in order on a GaAsP substrate 1, and a device structure is obtained. When a GaInP epitaxial layer 2 doped with Si is formed, a layer of low dislocation density having a flat surface is obtained. Hence, when an LED or an LD is formed by using the semiconductor material obtained by this invention, the quality and the reliability can be remarkably improved. The above material is especially effective for orange to blue light emitting elements.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to direct transition type III
-Light emitting diodes (LEDs) and semiconductor lasers (L
D) and other materials for semiconductor devices.

0002

[Background Art] GaInP, which is a III-V group compound semiconductor material and whose main component is GaInP, has the largest band gap among direct transition type III-V group compound semiconductors excluding nitrides. It is the most advantageous material for composing light emitting elements that emit not only red light, but also green to orange light, and is currently used in red LEDs and L
It is used as a material for D.

[0003] These red LEDs are currently in practical use.
and LD are GaA obtained as high quality crystals.
GaInP is lattice-matched to GaAs using a s-substrate.
and a layer of AlGaInP mixed crystal.

That is, it is fabricated by directly growing an AlGaInP cladding layer and a GaInP active layer on a GaAs substrate without providing a compositionally graded layer on the substrate. In this system, [Aly Ga1-y ] x
In1-x P (0≦y≦1, x=0.51) is Ga
an active layer that is lattice matched to As and has a composition such that y=0, for example;
A red light-emitting device having a heterostructure with a cladding layer having a composition of y=0.7 can be obtained. In addition, by appropriately selecting the value of y of the active layer, it is possible to produce even shorter wavelengths (for example, yellow).
Light-emitting devices have also been obtained. Furthermore, it is theoretically possible to use a green light emitting element.

However, in order to obtain green to orange short wavelength light emission with this system, it is necessary to use AlGaIn containing Al.
The light emitting region must be formed of P, and the reliability and performance of the light emitting device are low due to the presence of Al, which is easily oxidized.

[0006] Therefore, AlGaIn with a low Al content
In order to use GaInP which does not contain P or Al as a light emitting region and to enable green to orange light emission, the mixed crystal [AlyGa1-y]x In1-x P of the light emitting part is
In this case, it is necessary to increase the values of y~0 and x from 0.51 to appropriate values, and it is also required to specially prepare a substrate that lattice matches such a mixed crystal.

For this purpose, a GaAs substrate or a GaP substrate is used.
A substrate has been developed in which a GaAsP composition gradient layer for lattice matching is provided on the substrate, and a GaInP-based second layer for lattice matching is grown on the GaAsP substrate.

[0008]

[Problem to be solved by the invention] However, the GaAsP
The substrate is usually produced by vapor phase epitaxy, but it has a lattice shape of about 2
It has a unique crosshatch pattern surface morphology formed from ridges with micrometer steps. Therefore, even if multiple layers are formed on the substrate, it is difficult to improve the surface morphology and a flat interface cannot be obtained.

Further, the GaAsP substrate has a large number of high-density misfit dislocations, and these dislocations usually propagate even if multiple layers are grown on the substrate. These cross-hatch patterns and high dislocation densities significantly impair the performance and reliability of LEDs and LDs when they are manufactured.

The present invention provides a semiconductor material in which a GaInP epitaxial layer with a flat surface and few dislocations is grown on a GaAsP substrate in order to realize a green to orange light emitting device of high quality and high reliability. With the goal.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have developed the following semiconductor material.

That is, as shown in FIG. 1, in the semiconductor material of the present invention, Si-doped Ga is deposited on a GaAsP substrate.
A buffer layer mainly composed of InP mixed crystal (hereinafter simply referred to as “
Also called a buffer layer. ) and a device layer (hereinafter also simply referred to as "device layer") mainly composed of GaInP mixed crystal are formed in sequence.

Further, a desirable embodiment of the material of the present invention is characterized in that the buffer layer and the device layer are formed by liquid phase growth.

The GaAsP substrate used in the present invention is, for example, a compositionally graded layer made of GaAsy P2y on a GaAs substrate, that is, a layer in which the value of y is gradually decreased (a layer in which the P content is gradually increased). ) can be used that are grown sequentially on a substrate.

[0015] GaAs on GaP or GaAs substrate
Conventionally known methods for epitaxially growing P include vapor phase growth (chloride method, halide method) and MOVPE.
A method selected from (organic metal vapor phase epitaxial growth method), MBE (molecular beam epitaxial growth method), LPE (liquid phase epitaxial growth method), etc. is used.

It goes without saying that the mixed crystal composition of the buffer layer on the GaAsP substrate needs to be lattice matched with the GaAsP substrate. The specific mixed crystal composition is GaP
When expressed as a molar fraction, it is 0.51 to 0.75, preferably 0.60 to 0.74. The mole fraction of GaP is selected depending on the desired orange to green emission wavelength. In addition, in the present invention, GaAsP
The mixed crystal forming the GaInP layer on the substrate ranges from AlGaInP mixed crystal with a low Al content to GaInP containing no Al.
Includes up to InP mixed crystal.

There are no particular restrictions on the means for growing the buffer layer and device layer on the GaAsP substrate, but the conventionally known LPE (liquid phase epitaxial growth method) may be used. In particular, the slide board method may be used to grow the buffer layer and the device layer. Desirable in terms of maintaining uniformity.

Buffer layers and device layers can be grown sequentially as a series of steps, typically using indium (In) as a solvent and a suitable dopant (such as Si).
gallium (Ga) and indium phosphide (In
A solution containing InP (P) or gallium phosphide (GaP) and InP can be prepared, and this solution can be sequentially grown on a substrate by known means. At this time, the amounts of InP and GaP or Ga and InP to be added to the In solvent are determined so that the mixed crystal composition of each GaInP growth layer precipitated from these solutions is 0.51 to 0.0 in molar fraction of GaP, as described above. 75 range. However, since a solution containing Ga and InP in an In solvent causes meltback, it is more preferable to prepare the GaInP layer using a solution of InP and GaP.

Dopant (Si) mixed into the buffer layer
) is about 1017 to 1019/cm3, preferably about 1018/cm3. The amount of Si added depends on the segregation coefficient at the growth temperature and the set carrier concentration. On the other hand, dopants mixed into the device layer include donor impurities such as S, Te, Sn, and Se.
Alternatively, it is an acceptor impurity such as Ge, Be, Cd, Mg, or Zn, and the amount of dopant is determined by the set carrier concentration.

The device layer can be grown sequentially after the buffer layer growth step or as a series of steps. The device layers are formed by diffusion or bilayer growth.
It is possible to form a bond and use it as a material for LEDs or LDs.

After the growth process of the buffer layer, a heterostructure of a GaInP active layer and an AlGaInP cladding layer is formed on the buffer layer by a vapor phase growth method such as MOCVD or MBE, thereby forming a material for LED or LD. It is also possible to serve it as

[0022] The thickness of the buffer layer can be set to 1 to 20 μm using the slide board method;
It is desirable to set it to 10 micrometers.

[0023] Although the function of Si has not been scientifically clarified, it appears in the lattice-like ridges forming the crosshatch pattern on the GaAsP substrate and in the epitaxial layer of dislocations that exist in large numbers in the GaAsP substrate. It is an experimental fact that it acts as a hindrance to the spread of.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The semiconductor material according to the present invention will be explained in detail below with reference to the drawings. FIG. 1 shows the structure of the semiconductor material of the present invention in which a buffer layer 2 and a device layer 3 are grown on a GaAsP substrate 1, and FIG. 2 shows the structure of the crystal growth apparatus used in manufacturing the material of the present invention. Outline.

First, expressed as the mole fraction of GaP, it is 0.0.
GaAsP with a mixed crystal composition of 5 to 0.45, (100)
Or GaP or GaA with (111) plane orientation
A GaAsP substrate 1 grown on an S substrate is prepared. The mixed crystal ratio of the substrate is uniquely determined by the composition that lattice matches the set composition of the GaInP mixed crystal.

Using this GaAsP substrate 1, a buffer layer 2 (hereinafter also referred to as "second layer") and a device layer 3 (hereinafter also referred to as "third layer") are grown by a slide board method.

Slider 1 of a crystal growth apparatus as shown in FIG.
3, the GaAsP substrate 1 is set. Then, a predetermined amount of In was cleaned by chemical etching and cleaning.
, InP, GaP and Si in a slide boat 10
into the solution reservoir 11a. Similarly, in the solution reservoir 11b,
Predetermined amounts of In, InP, GaP, S, and T to grow GaInP (device) layer 3, which is the third layer.
Donor impurities such as e, Sn, and Se are inserted. In addition,
The material to be inserted into the solution reservoir 11a is Si-In-Ga-P alloy, which is sufficiently mixed in advance using an appropriate method, and the material to be inserted into the solution reservoir 11b is In, which is mixed with donor impurities such as Se. -Ga-P alloy may be used.

To give a specific example of the amount of preparation, in the second buffer layer 2, InP is
60mg, GaP 40mg, Si 0.01~0.
1 mg, In3g in the third device layer 3
InP 60mg, GaP 40mg, Se
Charge 0.05 to 0.2 mg. Solution reservoir 11a, 1
After inserting these materials into the solution reservoirs 11a and 11b, lids 16 are attached to the solution reservoirs 11a and 11b, respectively, to prevent evaporation of phosphorus and the like.

The slide boat 10 is installed in a quartz tube 15 through which high-purity hydrogen purified by an appropriate method such as permeation through a palladium membrane or an inert gas such as high-purity nitrogen or argon is passed. After passing the above gas sufficiently so that no residual oxygen or water vapor exists in the quartz tube 15, the growth material is heated in an electric furnace 12 to a temperature slightly higher than the growth temperature of each layer, for example, 2 to 20°C higher. Each growth solution is homogenized by heating and holding at that temperature for a certain period of time (for example, 2 to 4 hours).

[0030] Thereafter, it is gradually cooled at an appropriate rate of 0.01 to 2.0°C/min to the growth starting temperature of the second layer, for example 820°C. At this time, the charging composition is adjusted so that the In solution for growing the second layer is in a supersaturated state where GaInP is saturated or almost saturated. Thereafter, the slider 13 is moved using the slider operating rod 17 to move the GaAsP substrate 1 directly below the solution reservoir 11a, and the growth solution in the solution reservoir 11a is brought into contact with the GaAsP substrate 1.

The solution is applied at a suitable rate, for example 0.01 to 2.
Since it is slowly cooled at 0 °C/min, GaIn
P becomes supersaturated and it is deposited on the GaAsP substrate 1 to form a buffer (Si-doped GaInP) layer 2.
grows. This second layer has a suitable thickness, for example 10μ.
When the temperature reaches about m, move the slider 13 and
The P substrate 1 is moved directly below the solution reservoir 11b, and a third device (GaInP) layer 3 is grown. When the thickness reaches a predetermined value, for example, about 20 μm, the slider 13 is moved again to move the growth solution in the solution reservoir 11b away from the surface of the device layer 3 so that the two do not come into contact with each other, thereby finishing the growth. .

In this manner, the buffer layer 2 having a predetermined GaInP mixed crystal composition, for example, a composition containing 70 mol % of GaP, and subsequently the device layer 3 can be obtained. When a device layer is formed directly on a GaAsP substrate,
The device layer has a dislocation density (EPD) of 1×105 c
The height difference of the lattice-like ridge having m-2 or more dislocations and forming a crosshatch was about 2 μm, but when the device layer was formed with a buffer layer interposed, the EPD was 1 × 104 cm- 2 or less, the step of the ridge is 0.5
They were reduced to below μm.

Since the third device layer 3 obtained by the above manufacturing example is contaminated with donor impurities such as Se, the conductivity type of the obtained GaInP crystal is usually n-type. Therefore, as shown in FIG.
By diffusing acceptor impurities such as Be, Cd, Mg, and Zn, the conductivity type of a part of device layer 3 (n type; 20 μm) is inverted to p type to form a pn junction, and device layer 4 (p
(type; 10 μm).

In addition, the third device layer 3 (n type;
0 μm), a GaInP crystal with a p-type conductivity is further formed using the LPE method (for example, the slide board method).
It is also possible to grow a device layer 4 (n-type; 20 μm) to form a pn junction as shown in FIG. The growth of the device layer 4 may be performed in the same manner as in the growth process of the device layer 3 described above, using an acceptor impurity such as Zn instead of a donor impurity such as Se.

Furthermore, it is also possible to grow a double heterojunction device layer, as shown in FIG.
l) GaInP active layer 6 and AlGaInP cladding layers 5 and 7 are formed by MOCVD or MBE instead of LPE.
It can also be grown by a vapor phase growth method such as.

In the above description, Ga is used as the seed crystal substrate.
Although the example using the (100) or (111) plane of AsP has been explained, any other plane can be used. Further, although it may be an off-board or a just-board, a board with an off-angle of 1 to 5 degrees preferably has better surface morphology.

[0037]

[Effects of the Invention] Since the semiconductor material of the present invention is constructed as described above, it exhibits the following effects.

A GaAsP substrate has many lattice-like ridges forming a unique crosshatch pattern and high-density misfit dislocations. Therefore, when normal epitaxial growth is performed, it is difficult to prevent the propagation of ridges and dislocations.

However, by forming a Si-doped GaInP layer (buffer layer) before forming the GaInP epitaxial layer, a layer with a low dislocation density and a flat surface can be obtained. Therefore, when an LED or LD is manufactured by forming a device layer on the buffer layer, its performance and reliability can be significantly improved.

Furthermore, by appropriately selecting the mixed crystal ratio of the GaAsP substrate, substrates with a wide variety of lattice constants can be manufactured and can be applied to various uses.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor element material showing one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a crystal growth apparatus used in manufacturing the material of the present invention.

FIG. 3 is a cross-sectional view of each semiconductor element material before and after growth in a modified example of the present invention.

FIG. 4 is a cross-sectional view of each semiconductor element material before and after growth in a modified example of the present invention.

FIG. 5 is a cross-sectional view of each semiconductor element material before and after growth in a modified example of the present invention.

[Explanation of symbols]

1: GaAsP substrate 2: Buffer layer (Si-doped GaI
nP layer) 3: Device layer (n-type GaI
nP layer) 4: Device layer (p-type GaI
nP layer) 5: n-type AlGaInP layer 6
:p-type (Al) GaInP layer 7
:p-type AlGaInP layer 10
: Slide boat 11a, 11b : Solution reservoir 12 : Electric furnace 13 : Slider 15 : Quartz tube 16 : Lid

Claims (2)

[Claims] [Claim 1] Si-doped G on a GaAsP substrate.
A buffer layer mainly composed of aInP mixed crystal and Ga
A semiconductor material having at least a structure in which device layers containing InP mixed crystal as a main component are sequentially formed. 2. The buffer layer and the device layer include:
2. The semiconductor material according to claim 1, wherein the semiconductor material is formed by liquid phase growth.