JPH0536396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming a heterointerface, and particularly to a method for forming a high quality heterointerface of a compound semiconductor by molecular beam epitaxy.

(Prior Art) Most compound semiconductor devices such as two-dimensional electron gas transistors and quantum well lasers utilize heterojunctions in which different types of semiconductor crystals are joined. The properties of the heterojunction interface (hereinafter referred to as heterointerface) affect carrier scattering, light emission, absorption, etc., and greatly influence device characteristics.
Therefore, it is important to form a high-quality interface that is flat, steep, and free of impurities and defects. Molecular beam epitaxy (hereinafter referred to as MBE) is widely used as a means of forming steep hetero-interfaces.

Figure 2 shows a schematic cross-sectional view of the MBE device. M.B.E.
The method uses molecular beam sources 20 and 21 that heat raw materials containing elements constituting a desired crystal and eject them in the form of molecular beams in a growth chamber 1 maintained at an ultra-high vacuum by a vacuum pump 9 such as an ion pump. , 22 and this molecular beam source 2
A substrate holder 3 whose temperature can be controlled independently of the substrates 0, 21, and 22 is provided, and molecular beams of raw material elements are ejected from molecular beam sources 20, 21, and 22 toward the substrate 4 to perform epitaxial growth. be. M.B.E.
In this method, the molecular beam intensity can be modulated and controlled by opening and closing the shutter 5 to intermittent individual molecular beams and by setting the temperature of the evaporation source.

A conventional method for forming a flat and steep interface on the order of atoms is to interrupt the growth at the interface by closing the shutter 5 during MBE growth, and wait for several tens of seconds to several minutes to increase the flatness of the interface. has been reported for the GaAs/AlGaAs hetero system (Japanese journal off.
Applied Physics, (Jpn.J.Phys.24
(1985) page L417). In this method, atoms on the substrate surface move around on the surface during waiting, are captured by steps and kinks on the surface, and gradually form larger islands. In the well-controlled MBE of GaAs and AlGaAs heterogrowth, the width of the interface transition region is 1
It is a molecular layer. Therefore, extremely flat islands with a height of one molecular layer thick are formed at the interface.

(Problems to be Solved by the Invention) However, while the growth is interrupted and the growth is on standby, impurities present in the growth chamber 1 are adsorbed onto the substrate surface. For this reason, when forming a light emitting device using a semiconductor device made of GaAs and AlGaAs formed by flattening the interface in this way, such as a quantum well, the emission spectrum width is narrowed, but the luminous efficiency is reduced. There's a problem.

An object of the present invention is to provide a method for forming a high-quality heterointerface that solves this problem.

(Means for Solving the Problems) The interface forming method of the present invention is a method for forming a first compound semiconductor in molecular beam epitaxy in which molecular beams containing elements constituting a desired crystal are deposited on a substrate kept at a temperature. a first epitaxial growth step in which crystals are deposited; a standby step in which the first epitaxial growth is stopped and the temperature of the substrate is held higher than in the first epitaxial growth step; The method is characterized in that it subsequently includes a second epitaxial growth step in which a second compound semiconductor crystal is deposited while maintaining the temperature of the substrate at a lower temperature than in the standby step.

(Function) This interface formation method increases the surface diffusion rate of atoms by raising the substrate temperature during standby at the interface compared to during growth, thereby reducing the time required for planarization and reducing the amount of impurities adsorbed. Furthermore, by increasing the substrate temperature, the probability of impurities being adsorbed onto the surface itself is reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1a shows the interface forming method of the present invention,
FIG. 1b, which is a graph of the change in substrate temperature over time, is a photoluminescence (hereinafter referred to as PL) spectrum at 77K of a quantum well formed according to the present invention. Figure 2 is used in the present invention.
FIG. 2 is a schematic cross-sectional view of the MBE device.

Here, we will describe an example in which a quantum well structure is formed on a GaAs substrate, with a GaAs quantum well sandwiched between Al _0.5 Ga _0.5 As barrier layers. The general configuration of the MBE device shown in FIG. 2 has already been described. Molecular beam source 2
0 is filled with Ga, 21 with Al, and 22 with As as raw materials. GaAs was first organically cleaned using conventional methods and cleaned by chemical etching.
(100) Growth chamber 1 with substrate 4 evacuated to 10 ^-10 Torr
It is attached to the board holder 3 inside.

Prior to growth, Ga and Al molecular beam sources 20,2
1, the temperature is set to obtain the desired composition of Al _0.5 Ga _0.5 As, and the As molecular beam source 22 is also set at approximately 1×10 ^-5 Torr.
The temperature is set so that a molecular beam intensity of 1 is obtained at the position of the GaAs substrate 1. While the shutter 5 in front of the As molecular beam source 22 is used to irradiate the GaAs substrate 4 with As molecular beams, the temperature setting of the heater built into the substrate holder 3 is raised to thermally clean the surface of the GaAs substrate 4 under As pressure. Normally, at 580 degrees, the oxide film on the surface is removed and the surface becomes clean. The substrate temperature is stably controlled at 600° C., the shutter 5 in front of the Ga and Al molecular beam sources 20 and 21 is opened, and a barrier layer of Al _0.5 Ga _0.5 As is grown (first epitaxial growth). The growth layer thickness was 0.5 μm.

Next, the Ga and Al shutters 5 are closed to interrupt the growth, and at the same time, the temperature setting of the heater of the substrate holder 3 is raised to 680° C., and the substrate is left under As irradiation for 10 seconds (standby step).

Next, set the substrate temperature to 600℃ again, and at the same time,
Open the shutter 5 in front of the Ga molecular beam source 20.
GaAs is grown to about 28 Å (about 10 molecular layers) (second epitaxial growth step). This forms a heterointerface on one side of the quantum well.

Then, the Ga shutter 5 is closed again to interrupt the growth, the substrate temperature is set to 680° C., the substrate 4 is irradiated with only As, and the process is waited for 10 seconds (standby step).

Next, the substrate temperature is returned to 600°C, the Ga and Al shutter 5 is opened, and the Al _0.5 Ga _0.5 As barrier layer is formed.
A quantum well layer structure is formed by growing 0.5 μm.

When the PL spectrum of the quantum well formed in this manner is measured at 77K, two peaks are seen as shown in the solid line spectrum in Figure 1b. Each peak corresponds to a GaAs layer whose thickness differs by one molecular layer.
It corresponds to PL emission from quantum wells, that is, quantum wells with thicknesses of 4.5a ₀ and 5.0a ₀ (a ₀ is the lattice constant of GaAs). The dashed line shows the spectrum obtained when waiting for 3 minutes using the conventional interface formation method. In this case as well, there are two peaks, indicating that the interface is flattened and islands are formed, but the emission intensity has fallen to about 1/3 of that in the case of the present invention.

As described above, according to the present invention, the luminous efficiency is high.
Quantum wells with high quality interfaces can be obtained.

In the above embodiments, a quantum well was used as an example, but modulation doping to the hetero interface was performed.
Needless to say, the method for forming a heterointerface of the present invention is effective in improving the quality of the interface in dimensional electron gas systems and the like.

It goes without saying that the present invention is also effective for other material systems such as InGaAs/InAlAs.

(Effects of the Invention) As described above, according to the heterointerface formation method of the present invention, the interface is formed from a flat island region with the height of a monomolecular layer, and is not only extremely flat and steep, but also Low impurities. As a result, the emission spectrum is narrow and the intensity is strong, making it suitable for applications in the production of various semiconductor elements, such as the production of light-emitting and light-receiving devices. Also,
Since the interface is flat and there are few pure substances, it is suitable for application to the production of electronic devices using carrier rotation development at a heterointerface.

[Brief explanation of the drawing]

FIG. 1a is a graph of changes in substrate temperature over time to explain the method of forming a heterointerface of the present invention, and FIG. 1b is a
FIG. 3 is a photoluminescence spectrum diagram at 77k of a quantum well formed according to the present invention. FIG. 2 is a schematic cross-sectional view of a molecular beam epitaxy apparatus used in the present invention. In the figure, 1... growth chamber, 20... Ga molecular beam source,
21...Al molecular beam source, 22...As molecular beam source, 3
. . . substrate holder, 4 . . . substrate, 5 . . . shutter, 9 . . . ion pump, respectively.

Claims (1)

[Claims] 1 In molecular beam epitaxy growth, in which atoms or molecules are deposited on the substrate by irradiating a molecular beam containing elements constituting a desired crystal onto a substrate held at a predetermined temperature, the first step is to deposit the first atoms or molecules. an epitaxial growth step, a standby step in which the first epitaxial growth is stopped and the temperature of the substrate is held higher than in the first epitaxial growth step, and subsequent to the standby step, A method for forming a heterointerface, comprising at least a second epitaxial growth step of depositing second atoms or molecules while maintaining the temperature of the substrate at a temperature lower than that of the standby step.