JPH0144680B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an MBE growth method for forming a single crystal thin film periodic structure used as a microwave device or a light emitting/light receiving device. For example, the first
In a quantum well laser as shown in the figure,
It is necessary to alternately and periodically form different types of layers with thicknesses of several tens of angstroms to several hundreds of angstroms in the light emitting part, and the present invention relates to an MBE growth method for forming such a structure.

(Prior art and its problems) Figure 2 is a diagram for explaining the conventional MBE growth method for forming a - group compound semiconductor thin film periodic structure, and is a schematic diagram of the growth chamber of the MBE apparatus seen from above. be. A similar schematic diagram can be found, for example, in the patent publication Showa
57-47160, and Japanese Unexamined Patent Publication No. 57-11899 describes the opening/closing operation of the cell shutter, which is a problem with the prior art described below. Furthermore, a detailed explanation of the MBE growth method and devices using thin film periodic structures can be found in Nikkei Electronics No. 308 (1983).
(by WTTsang) etc.

In Fig. 2, 1 is a substrate holder, 2 is a substrate, 3 is a cell shutter, 4 is a group material A (eg, Ga), 5 is a cell, 6 is a cell shutter, and 7 is an A
Group raw material B (for example, Al), which is different from the above, and 8 are cells. In conventional MBE growth to form a periodic structure of - group compound semiconductor thin films, the substrate 2 held on the substrate holder 1 is placed in the growth chamber at a position where the center axes of cells 5 and 8 intersect, and growth is performed. It will be done. Then, the molecular beam of group raw material A4 evaporated from cell 5 and
By alternately opening and closing the cell shutters 3 and 6 at a predetermined period, the molecular beams of the group raw materials B7 evaporated from the cell 8 are applied to different types of group raw materials A and B on the substrate 2. Group compound semiconductor thin films are alternately and periodically formed.

According to the above steps, for example, while the cell shutter 3 is open, the cell shutter 6 is closed. By the way, when a - group compound semiconductor is grown by MBE, the cell temperature of the group raw material is generally heated to a high temperature of 700 to 1000°C. Therefore, by closing the cell shutter 6 while the cell shutter 3 is open,
The cell shutter 6 is heated, and the cell temperature itself is also subjected to disturbances caused by the cell shutter. When the cell shutter is heated, impurity molecules are evaporated from the cell shutter and incorporated into the growing thin film, resulting in deterioration of the electrical properties of the thin film. FIGS. 3 and 4 show measurement results regarding the above contents. Figure 3 shows
These are the results of using a quadrupole mass spectrometer to investigate changes in the amount of _impure gas after ^the cell shutter was closed ^.
It can be seen that the mass peak intensity increases, albeit momentarily, and the amount of impure gas increases. Furthermore, Figure 4 shows the results obtained for an InGaAs single crystal thin film, for example, and the electron mobility decreases as the residual impurity carrier concentration within the thin film increases, indicating that the electrical characteristics deteriorate. I understand.

Apart from the problem of impure gas generation from the cell shutter as mentioned above, closing the cell shutter causes fluctuations in the cell temperature itself, and as a result, when the cell shutter 6 is opened again, the group raw material B7 causes an overshoot in the molecular beam intensity. This makes it difficult to control the thickness of the - group compound semiconductor thin film made of the group raw material B7 and the composition in the case of a mixed crystal. FIGS. 5, 6, and 7 show measurement results regarding the above contents in the case of a mixed crystal containing In and Ga as group elements. FIG. 5 shows the results of measuring changes in Ga molecular beam intensity (Torr) using a vacuum gauge when the cell shutter was closed for about 3 minutes and then reopened. It can be seen that immediately after opening the cell shutter, the molecular beam intensity (Torr) overshoots, and then it takes 1 to 2 minutes to stabilize to the original molecular beam intensity (Torr.). Although the magnitude of overshoot is different, the same phenomenon is
It was also observed in In molecular beam intensity. Figure 6 also shows, for example, when InxGa _1-x As is grown on an InP substrate.
|△a/aInP|(△α=
αInGaAs−〓InP,〓InGaAs is the lattice constant of InGaAs,
αInP is the lattice constant of InP) and shows the influence of the flux intensity ratio of In and Ga. The overshoot of the Ga molecular beam intensity (Torr) in Fig. 5 directly leads to a decrease in the controllability of the flux intensity ratio in Fig. 6, and |△a/a|
The composition controllability of the InxGa _1-x As single crystal thin film also deteriorates.
As a result of Auger electron spectroscopy (AES) analysis of the composition distribution in the thickness direction of the In _x Ga _1-x As layer grown by MBE in the presence of an overshoot as shown in Fig. 5, the results are as shown in Fig. 7. , a gradient is observed in the composition ratio of In and Ga immediately after the cell shutter is opened, that is, near the InxGa _1-x As/InP substrate interface, indicating poor composition controllability. Also, Figure 7 shows the same
Group (Ga, _In ) molecular beam _intensity (Torr.) and growth rate (μ
This figure shows the experimental results obtained regarding the correlation with m/hr.). In the case of Figure 5, the Ga molecular beam intensity (Torr.) is increased due to overshoot.
has increased to about 1.2 to 1.4 times the original intensity, and overshoot has also been observed in the In molecular beam intensity (Torr.).
The Ga+In beam intensity shown in the figure is also 1.2 to 1.4 times higher, and the growth rate is also 1.2 to 1.4 times higher. In this way, immediately after opening the cell shutter,
The growth rate is higher than the designed value, which deteriorates the thickness controllability of the thin film. In this way, in the conventional MBE growth method for forming a periodic structure of a - group compound semiconductor thin film as shown in FIG. 1, the generation of impurity gas and This causes fluctuations in the molecular beam intensity, which deteriorates the electrical properties of the thin film and adversely affects the film thickness or, in the case of mixed crystals, the composition controllability, and when a periodic structure of the thin film is formed. This has the disadvantage of causing periodicity deterioration.

(Structure of the Invention) An object of the present invention is to provide an MBE growth method that reduces the electrical property deterioration and periodicity deterioration of the - group compound semiconductor thin film periodic structure that occurs with the opening and closing of the cell shutter described above.

The present invention will be described in detail below with reference to the drawings.

FIG. 9 is a diagram for explaining an embodiment of the MBE growth method of the present invention, and is a view of the growth chamber viewed from above. 9 and 10 are group raw materials A, B, 11, and
12 is a molecular beam cell. The central mask 13 has a hole in the shape of a circle or the like, and the group molecule 1
Group molecules A and B that have jumped out from 1 and 12 pass through this hole and reach positions 14 and 15, respectively. The substrate holder 16 is rotated around an axis 17 and passes through the positions of the guides 14 and 15. Therefore, on the substrate 18, a - group semiconductor thin film consisting of group molecules A is grown at position 14, and a - group semiconductor thin film consisting of group molecules B is grown at position 15. Since the substrate holder is rotating, These semiconductor thin films are grown alternately in layers. For example, group elements include As, group element A,
If In and Ga are used for B, respectively, a laminated multilayer structure of InAs-GaAs can be formed.

In FIG. 9, the period of the - group compound semiconductor single crystal thin film periodic structure can be easily changed by changing the rotation speed of the substrate holder. In addition, the ratio of the film thickness of the - group compound semiconductor thin film made of group raw material A and the - group compound semiconductor thin film made of group raw material B can be determined by adjusting the cell temperature of each group in advance. It can be easily changed by changing the intensity ratio.

In the method of growing a thin film periodic structure according to the present invention as shown in FIG. 9, the cell shutter is always open and needs to be closed only when growth is finished. As a result, the generation of impurity gas and fluctuations in the molecular beam intensity, which are problems with the conventional MBE growth method in which the cell shutter is periodically opened and closed, do not occur during growth, and the amount of impurities contained is small and periodicity is reduced. A good - group compound semiconductor thin film periodic structure can be formed.

The main effect of the present invention is that it can solve the problems of impurity gas generation and molecular beam intensity fluctuation, but for example, as shown in FIG. Alternatively, if a large substrate holder including regions 14 and 15 is provided, a plurality of substrates are attached to it, and the substrate holder is rotated, a substrate wafer having a periodic structure of a single crystal thin film with the same period can be obtained.
It is now possible to obtain multiple sheets with one growth, and it is also expected to have the effect of improving mass productivity.

(Effects of the Invention) The effects of the present invention are that impurity gas generation from the cell shutters is prevented by rotating the substrate holder with each cell shutter always open by providing a mask with holes in the growth chamber. In addition, it is possible to eliminate fluctuations in molecular beam intensity, and as a result, it is possible to easily form a fine single-crystal thin film periodic structure with extremely good periodicity.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a quantum well laser; Figure 2 is a schematic diagram of a quantum well laser;
The figure is a diagram for explaining the conventional MBE growth method for forming a - group compound semiconductor single crystal thin film periodic structure, Figure 3 is the measurement result regarding impurity gas generation from the cell shutter, and Figure 4 is _0.53
Figure 5 shows the measurement results of the relationship between the residual impurity carrier concentration and electron mobility of a Ga _0.47 As single crystal thin film, and Figure 6 shows the measurement results of the molecular beam intensity overshoot immediately after the cell shutter is opened.
Figure 7 shows the measurement results of the relationship between the In _x Ga _1-x As composition and the group ₍ In and Ga) molecular beam intensity ratio.
The AES analysis results in the thickness direction of the Ga _1-x As layer, Figure 8, show the growth rate of the In _0.53 Ga _0.47 As single crystal thin film,
FIG. 9 is a diagram for explaining the MBE growth method of the present invention, showing the measurement results regarding the relationship with the group (Ga+In) molecular beam intensity. A...P-type GaAs, B...P-type GaxAl _1-x As,
C...Non-doped GaAs well, D...Non-doped GaxAl _1-x As barrier, E...n-type GaxAl _1-x As,
F...n-type GaAs, 1,16...substrate holder,
2, 18... board, 3, 6... cell shutter,
4, 9... Raw material A, 5, 8, 11, 12... Cell, 7, 10... Raw material B, 17... Rotating shaft, 13
. . . Mask with holes, 14 . . . Region where raw material molecules A reach, 15 . . . Region where raw material molecules B reach.

Claims (1)

[Claims] 1. In a method for forming a periodic structure of a - group compound semiconductor single crystal thin film by MBE growth, a mask with one hole is provided in the growth chamber, the growth chamber is filled with group V molecules such as As, and group V molecules such as A _s are collected from multiple group molecule cells. By rotating the substrate holder around a specific axis so that the emitted molecular beam passes through the hole in the central mask and hits the semiconductor substrate on the substrate holder, different − group semiconductor thin films are periodically and continuously grown. Characteristic MBE growth method.