JPH04323880A - Material for gallium nitride-based semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To obtain a material for blue-ultraviolet band semiconductor light emitting element optimum for a display, an optical communication, etc., having a high light output efficiency. CONSTITUTION:A material for a gallium nitride-based semiconductor light emitting element having a structure in which with a surface 4 rotated at 9.2 degrees from a face R [plane (1,-1, 0, 2)] sapphire at a face R projection 3 of c-axis of the sapphire as a rotating axis, as a reference surface, a surface having an OFF angle being + or -2 degrees or less is used as a substrate surface, and at least one type of gallium nitride-based semiconductor layer is laminated on the substrate, is manufactured by using a CBE melthod, etc., without using an AlN buffer layer, etc. This material for the element is flat in a thin film thickness, and a material for a blue-ultraviolet band semiconductor light emitting element adapted for a display, an optical communication, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is particularly applicable to displays,
The present invention relates to materials for semiconductor light emitting devices such as ultraviolet to blue light emitting diodes and laser diodes, which are optimal for optical communications.

0002

[Prior Art] Semiconductor light emitting devices, particularly visible light emitting diodes (LEDs), are used as functional display devices in all fields, but until now semiconductor light emitting devices in the ultraviolet to blue range have not been put to practical use. Development is urgently needed for displays that require three primary colors. Ultraviolet to blue semiconductor light emitting devices include ZnSe, GaN, and SiC.
It has been reported that the use of

[0003] Gallium nitride (GaN) is often deposited on the C-plane of sapphire by the MOCVD method or the VPE method [Journal of Applied Ph.D.
ysics, 56 P. 2367-2368 (198
4)], but in order to obtain a flat surface, generally 20 to 3
A film thickness of 0 μm or more is required, and even if an AlN buffer layer is used, a film thickness of at least about 4 μm or more is required [A
pplied Physics Letter, 48
P. 353-355 (1986)].

[0004] GaN semiconductor light emitting devices generally receive light from the substrate side [National Techni
cal Report, 28 P. 83-92 (1
982)], in a semiconductor light emitting device that requires a thick film, a decrease in light extraction efficiency is inevitable. In this way, conventional GaN-based thin films for semiconductor light-emitting devices have a large lattice mismatch with the C-plane sapphire substrate, and when the film thickness is less than 1 μm, the lattice mismatch at the interface has a large effect on the morphology of the GaN thin film surface, resulting in a flat surface. Single crystal thin films cannot be obtained. Therefore, in order to alleviate lattice mismatch, a film thickness of 20 to 30 μm or more is required, and even if an AlN buffer layer is used, a film thickness of 4 μm or more is required, resulting in a decrease in light extraction efficiency [Journal of the Crystallographic Society of Japan 15th page. 334-342 (1988)].

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a thin and flat GaN-based single crystal thin film in order to increase light extraction efficiency.

[0006]

[Means for Solving the Problems] As a result of extensive research to solve the above problems, the present inventors have developed an AlN buffer by using a surface rotated in a specific direction from the sapphire R surface as the substrate surface. The present invention was realized based on the discovery that planarization of a GaN-based thin film can be achieved with a small film thickness without the need for operations such as forming layers.

[0007] That is, the present invention provides, from the sapphire R surface,
The surface rotated by 9.2 degrees using the R-plane projection of the sapphire c-axis as the rotation axis is used as the reference plane, and the surface with an off angle of plus or minus 2 degrees or less is the substrate surface, and at least one type of gallium nitride-based The present invention provides a gallium nitride-based semiconductor light emitting device material characterized by having a structure in which semiconductor layers are stacked.

The present invention will be explained in more detail below. In the present invention, the sapphire R plane refers to (1, -1, 0,
2) Surface (R surface). Also, sapphire c
The R plane projection of the axis is the R plane projection of the c axis of the unit vector in the sapphire single crystal (corundum type hexagonal crystal) unit cell.
It is a projection onto a surface (Figure 1).

Further, the reference plane in the present invention is a plane rotated by 9.2 degrees from the sapphire R plane using the R plane projection of the sapphire c-axis as the rotation axis (FIG. 2). and,
This angle of deviation from the reference plane is called an off-angle, and a surface with an off-angle of plus or minus 2 degrees or less is the substrate surface on which a GaN-based thin film is formed. By using this substrate surface, the lattice mismatch between the sapphire substrate and the GaN-based thin film can be suppressed to about 1%, and the surface is flat even at a film thickness of 1 μm or less, and the GaN-based thin film has good single crystallinity. can be obtained. When the off-angle becomes large, the surface becomes uneven and the single crystallinity also deteriorates. Further, this off-angle can be confirmed by X-ray diffraction method.

[0010] Next, the at least one kind of gallium nitride compound layer in the present invention is, for example, GaN or Ga1-
x Alx N, Ga1-x Inx N, Ga1-x
Mixed crystal compounds mainly composed of GaN such as BxN, or Zn, Mg, Be, Cd, Si, Ge
, C, Sn, Hg, etc. are added in small amounts as impurities. By combining such gallium nitride-based compound layers, it is also possible to manufacture elements having complex structures such as duffle heterostructures, quantum well structures, and superlattice structures.

As an example, FIG. 3 shows the structure of a mis-type light emitting device. A surface rotated by 9.2 degrees from the sapphire R surface using the R surface projection of the sapphire c axis as the rotation axis (off angle 0.
5 degree or less) (5), an n-type GaN single crystal film (6) is laminated to a thickness of 0.8 μm, and an Mg-doped GaN single crystal high resistance film (7) is further laminated to a thickness of 0.05 μm. be. Moreover, Al was used for the electrodes (8) and (9).

[0012] The film forming method is generally known as
For example, CBE method, CVD method, MOCVD method, vacuum evaporation method, sputtering method, etc. can be used, and among them, CBE method is most preferable. The present invention will be explained in more detail with reference to Examples below.

[0013]

EXAMPLE An example in which a gallium nitride mis-type laminated film is formed by the CBE method will be described. The apparatus includes, in a vacuum container (10) as shown in FIG. C with (15)
A BE apparatus was used.

The evaporation crucible (11) contains Ga metal, (12
) was charged with Mg metal and heated to 1020°C and 270°C, respectively.
heated to. A gas cell (14) is used to introduce the gas,
It was installed so that gas was blown directly onto the substrate (16). NH3 gas was used as the introduced gas, and the amount introduced was 5cc/
It was set to min. The degree of vacuum in the vacuum container is 1 to 5 during film formation.
It was about x10-6 Torr.

[0015] The substrate has a surface (
(off angle of 0.5 degrees or less) and heated to 800°C. First, while supplying NH3 gas, the shutter of the Ga crucible was opened and film formation was performed to form a GaN thin film with a thickness of 0.8 μm. Next, the shutter of the Mg crucible was opened and doping was performed while further film thickness of 0.8 μm was formed. The layers were laminated to a thickness of 2 μm.

When the surface morphology of this laminated film was observed using SEM, it was found that the surface was extremely flat and had no irregularities. In addition, a RHEED (high-speed electron reflection diffraction) image showed a single crystal pattern with streaks, and it was found that a single crystal GaN thin film oriented in the plane was produced. In addition, He was applied to this laminated film as excitation light.
When photoluminescence (PL) was observed at room temperature by irradiation with a -Cd laser, blue light emission having a peak around a wavelength of 0.47 μm as shown in FIG. 5 was obtained. Further, when a light emitting element as shown in FIG. 3 was prototyped and its current-voltage characteristics were measured, it exhibited diode characteristics as shown in FIG. 6.

[0017]

Effects of the Invention: By using a unique sapphire substrate surface, the gallium nitride-based light-emitting device material of the present invention suppresses the lattice mismatch between the substrate and the film to about 1%, and has a flat and single-crystal property even in a thin film. The present invention provides a material for a light-emitting element in the blue to ultraviolet range with good properties.

[Brief explanation of drawings]

[Figure 1] Corundum-type hexagonal crystal of sapphire and R of the crystal
It is an explanatory view showing a plane and a c-axis.

FIG. 2 is an explanatory diagram showing a surface rotated by 9.2 degrees from the sapphire R surface using the R surface projection of the sapphire c axis as the rotation axis.

FIG. 3 is a schematic diagram of the structure of an example of a prototype semiconductor light emitting device.

FIG. 4 is a schematic diagram of an experimental apparatus used in carrying out Examples.

FIG. 5 is a spectrum diagram showing the photoluminescence measurement results of the laminated film obtained in Example 1.

6 is a graph showing the voltage and current measurement results of the semiconductor light emitting device obtained in Example 1. FIG.

[Explanation of symbols]

1 Sapphire R-plane 2 Sapphire c-axis 3 R-plane projection of sapphire c-axis 4 Surface rotated by 9.2 degrees from the sapphire R-plane using the R-plane projection of the sapphire c-axis as the rotation axis 5 Sapphire substrate 6 N-type GaN single crystal Film 7 Mg-doped GaN single crystal film 8 Al electrode 9 Al electrode 10 Vacuum vessel 11 Evaporation crucible 12 Evaporation crucible 13 Evaporation crucible 14 Gas introduction cell 15 Substrate heating holder 16 Substrate 17 Cryopanel 18 Valve 19 Liquid nitrogen trap 20 Oil diffusion pump 21 Oil rotary pump 22 Shutter 23 Shutter 24 Shutter

Claims (1)

[Claims] Claim 1: The reference plane is a plane rotated by 9.2 degrees from the sapphire R plane using the R plane projection of the sapphire c-axis as the rotation axis, and the substrate plane is a plane with an off angle of plus or minus 2 degrees or less. A gallium nitride semiconductor light emitting device material having a structure in which at least one type of gallium nitride semiconductor layer is laminated on a substrate.