JPH0425238B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for manufacturing a - group compound semiconductor element, which is considered to be the most promising blue light emitting material.

(a) Prior Art Liquid phase growth and vapor phase growth are well known methods for manufacturing semiconductor devices. Furthermore, in recent years, the superiority of molecular beam epitaxial method has been recognized and it is used for forming various semiconductor devices. Regarding the molecular beam epitaxial method, JP-A-57-188889, JP-A No. 58
-86731 publication etc. are publicly known.

(c) Problems with the conventional technology The above semiconductor formation method is mainly based on - group (GaAs
etc.) - Group (SiC, etc.) compound semiconductors have been used and put into practical use, but - group compound semiconductors (ZnS, etc.) have not been put into practical use by these methods. If it becomes possible to control P-type and N-type conductivity by forming a single-crystalline thin film of - group compounds, progress in optoelectronic devices such as blue light-emitting diodes and short-wavelength lasers is promised.

However, in the formation of - group compound semiconductors, the liquid phase growth method and the vapor phase growth method grow in an almost thermal equilibrium state, so the growth substrate on which the single crystal thin film is grown must be heated to a high temperature. As the number of vacancies in the formed thin film increases, impurities are mixed in, resulting in a large number of lattice defects. If a large number of lattice defects or impurities are present in the crystal, P-type/N-type conductivity cannot be controlled due to self-compensation effects, etc., and the crystal cannot be used as an element.

On the other hand, molecular beam epitaxial method (hereinafter referred to as MBE)
It is abbreviated as ) is a reaction in a non-thermal equilibrium state, so the growth substrate temperature does not need to be high, and lattice defects due to vacancies and impurities can be suppressed to a much lower level than in the liquid phase growth method or vapor phase growth method. However, lattice defects are always included in crystals, and because - group compound semiconductors have strong ionic bonding, self-compensation is remarkable.
Even if lattice defects are suppressed as much as possible by MBE, adding a dopant will cause P due to the self-compensation effect.
It is extremely difficult to control type and N-type conductivity.

(d) Purpose of the Invention The primary purpose of the present invention is to grow a single crystal thin film of a - group compound with good crystallinity, thereby making it possible to control P-type and N-type conductivity.
The second purpose is to form a group compound semiconductor device.

(E) Summary of the Invention In order to achieve the above object, the present invention provides a method for supplying a molecular beam source made of a solid group element to a growth substrate as a molecular beam by an appropriate means, and a molecular beam source consisting of a gas containing a group element. is supplied to the growth substrate as a molecular beam of a monomer or a mixture of a monomer and a dimer decomposed by an appropriate means, and the relative intensity of both molecular beams is appropriately changed to obtain a stoichiometric composition. It is characterized by forming an epitaxial layer.

(F) Example FIG. 1 shows an example of the present invention, and is a schematic diagram of an experimental apparatus conducted by the present inventors.

In the figure, reference numeral 1 denotes a semiconductor growth apparatus, in which a gas cell 3 extends into a chamber 2, Knudsen cells 4 and 5, a growth substrate 6 disposed in the chamber, and a substrate stand 7 that holds this substrate 6. , shutters 8 and 9 disposed near the molecular beam emission ends of the Knudsen cells 4 and 5, respectively, and a shutter 10 disposed near the substrate 6, which serves as a molecular beam source for the gas cell 3.
_H2S gas cylinder 11, valve 12 of this cylinder 11, flow rate adjustment valve 1 connected to this valve 12
3. It is composed of a variable leak valve 14 that connects the flow rate adjustment valve 13 and the gas cell 3, and an exhaust device 15 that maintains the inside of the chamber 2 at a desired atmospheric pressure. Note that other components (for example, a device for RHEED pattern measurement, exhaust devices other than those mentioned above, valves, mass spectrometers, etc.) are omitted.

FIG. 2 is a sectional view of a main part of the gas cell 3 in FIG. 1. This gas cell 3 has a heat wire 17 passed through a tube-shaped wall 16 made of quartz. Reference numeral 18 is a tantalum heat shield plate disposed around the wall 16 to suppress the influence of radiant heat from around the wall 16.

In the above experimental apparatus, Knudsen cell 4
Zn (zinc) as a molecular beam source in the inner group, Ga (gallium) as a dopant in the Knudsen cell 5,
Group element S (sulfur) as a molecular beam source for gas cell 3
The experiment was conducted using H ₂ S (hydrogen sulfide), a gas containing . First, a - group compound was grown without doping, that is, without a dopant, and its properties were measured.

FIG. 3 is a graph showing the ratio of Zn in grown ZnS (zinc sulfide) to the substrate temperature. Note that the temperature of the substrate 6 is controlled to a desired temperature by a heater in the substrate stand 7.

As can be seen from the figure, when the substrate temperature rises, the S-rich state occurs. This is because the gas H ₂ S containing group elements is decomposed as 2H ₂ S → 2H ₂ +S ₂ S ₂ → 2S ₁ by heating with the heat wire 17 of the gas cell 3, and the S molecular beam has two molecules. This shows that not only bodies but also monomers are included. According to the "Vacuum Handbook" published by Japan Vacuum Technology Co., Ltd., the vapor pressure curves of Zn, S monomer, S dimer, ΣS, and ZnS are expressed as shown in Figure 4, and the substrate It is evident that only the S monomer has a lower vapor pressure than Zn as the temperature increases.

Next, in order to investigate the size relationship between the monomer and dimer contained in the S molecular beam, we show the proportion of S monomer in ZnS grown with respect to the introduction pressure of H ₂ S gas. Figure 5 shows this. According to the figure, as the H ₂ S gas introduction pressure increases, the composition approaches the stoichiometric composition (the composition ratio of Zn and S in the grown ZnS is 1:1).

Figure 6 shows the molar fraction of S monomer (S ₁ in the figure) with respect to the H ₂ S gas introduction pressure, the decomposition temperature (Tcr in the figure) by the heat wire in the gas cell 3, 1200〓,
For the four temperatures of 1300〓, 1400〓, 1500〓, Fig. 7 shows the mole fraction of S dimer (S ₂ in the figure) against the gas introduction pressure of H ₂ S, for the same four temperatures as above. Each is shown below. From both figures, it can be seen that as the H ₂ S gas introduction pressure increases, the mole fraction of S monomer decreases and the mole fraction of S dimer increases. Fifth
In the experiment shown in the graph shown in the figure, the decomposition temperature was 920℃ (=
1193〓), which is considered to be almost the same as the curve for the decomposition temperature 1200〓 in Figures 6 and 7.
In the experiment shown in the graph of FIG. 5, it can be considered that more S dimers exist in the molecular beam than S monomers. This is because when the H ₂ S gas introduction pressure is low, a large amount of S monomer is generated (as is clear from Figure 4, the adhesion coefficient is approximately 1).
However, due to the increase in the H ₂ S gas introduction pressure, S monomers decreased and S dimers increased, and due to the complementarity between Zn and S dimers. This is because it is considered that the composition approaches the stoichiometric composition.

From the above, the group molecules that make up the molecular beam produced by thermal decomposition of H ₂ S gas are a mixture of S monomers and dimers, with the dimer being more abundant. I understand that.

FIG. 8 shows the ratio of Zn in ZnS to changes in Zn molecular beam intensity. This eighth
As shown in the figure, as the Zn molecular beam intensity increases from the S-rich state, the composition approaches the stoichiometric composition. It is clear that the Zn-rich state is maintained and then becomes a Zn-rich state, similar to other compound semiconductors grown by MBE.

In Figure 9, the H ₂ S gas introduction pressure is 3×10 ^-5 [Torr], the substrate temperature is 360°C, and the H ₂ S gas decomposition temperature is 920°C.
This graph shows the ratio of Zn in grown ZnS to Zn molecular beam intensity determined from experimental data. From this graph, it can be seen that a stoichiometric composition is achieved when the molecular beam intensity of Zn is increased to around 9×10 ¹⁵ [Mole/cm ² ·s]. the above
Since the S molecular beam intensity is approximately 7×10 ¹⁴ [Mole/cm ²・s] based on the H ₂ S gas introduction pressure and decomposition temperature, Zn
When the molecular beam intensity ratio between S and S is around 13:1, the state shifts from an S-rich state to a stoichiometric composition. This molecular beam intensity ratio of about 13:1 varies depending on factors such as the temperature of the growth substrate, but the fact that the Zn molecular beam is stronger than the S molecular beam is not dependent on these factors. This is due to the S monomer being included in the S molecular beam.

Figure 10 shows the Zn molecular beam intensity 9×10 ¹⁵ [Mole/cm ²・
This is the RHEED pattern of the ZnS surface grown at the time of s], and it can be seen that a good surface (single crystal thin film) has grown.

In FIG. 8, the S-rich region is designated as A, the Zn-rich region as B, the portion of the stoichiometric composition region near the S-rich region as C, and the portion as close to the Zn-rich region as D. Among these regions, the regions C and D have good crystallinity, so the C and D regions may be doped to control N-type and P-type conductivity to form a semiconductor element. The C part has a stoichiometric composition, but strictly speaking it tends to be S-rich, and the D
On the contrary, there is a tendency towards Zn richness in some parts. Therefore,
By adding a dopant (donor) to substitute the Zn lattice position in the C part and a dopant (acceptor) to substitute the S lattice position in the D part, the dopant can easily enter the ZnS during the growth process. At this time, even if a self-compensation effect occurs due to doping and a vacancy is created in Zn, this vacancy cannot be collapsed because the molecular beam intensity of Zn is larger than that of S as described above. ,Also,
Even if an S vacancy occurs, the S monomer stays in the substrate for a long time, so this vacancy can be collapsed.

FIG. 11 is a graph showing the photoluminescence characteristics of a semiconductor device doped with Ga in the C portion. From the graph in FIG. 11, it is clear that
It can be seen that ZnS is formed. Similarly,
If a dopant, such as P, is doped to replace the S lattice position in the D part of FIG. 8, the P-type
Needless to say, ZnS is formed.

In this example, ZnS was formed as the - group compound semiconductor element, but ZnSe
The same applies to other - group compound semiconductor devices such as (zinc selenide).

In addition, in this example, the group molecular beam was supplied using a gas cell, but the gas cell was used because the vapor pressure of group elements is high and it is difficult to control the molecular beam intensity using a Knudsen cell. can be,
Any device other than the gas cell may be used as long as it can supply a molecular beam source made of a gas containing group elements as a molecular beam of a decomposed monomer or a mixture of a monomer and a dimer. In this case, a monomer of a group element or a mixture of a monomer and a dimer includes not only a case where a multimer of a group element is not completely contained but also a small amount that does not cause a problem in semiconductor formation. Including cases where there are.

Furthermore, it goes without saying that the molecular beam of the group and the molecular beam of the dopant may be supplied by a method other than the Knudsen cell shown in the Examples.

(G) Effects of the Invention According to the present invention described above, it is possible to form a - group compound semiconductor with few lattice defects, high quality, and capable of controlling P/N type conductivity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus showing an embodiment of the present invention, FIG. 2 is a sectional view of a main part of the gas cell in FIG. 1,
Figure 3 is a graph showing the ratio of Zn in grown ZnS, Figure 4 is the vapor pressure curve of Zn, S, and ZnS, and Figure 5 is the ratio of S in ZnS to the H ₂ S gas introduction pressure. Figure 6 is a graph showing the mole fraction of S monomer in the S molecular line versus the H ₂ S gas introduction pressure, and Figure 7 is a graph showing the S monomer mole fraction in the S molecular line versus the H ₂ S gas introduction pressure. Graph showing mole fraction of dimer, No. 8
The figure shows Zn in grown ZnS versus Zn molecular beam intensity.
Figure 9 is a graph of the experimental value, and Figure 10 is a graph of the general theoretical value showing the proportion of ZnS.
Photograph showing the RHEED pattern on the surface of a single crystal thin film,
FIG. 11 is a graph showing the photoluminescence characteristics when a ZnS single crystal thin film is doped with Ga. DESCRIPTION OF SYMBOLS 1... Semiconductor growth apparatus, 2... Chamber, 3... Gas cell, 4, 5... Knudsen cell, 6... Growth substrate, 7... Substrate stand, 8, 9, 10... Shutter, 17
...heat wire.

Claims (1)

[Claims] 1. A method for manufacturing a - group compound semiconductor device formed by a molecular beam epitaxial method, comprising:
A molecular beam source consisting of a solid group element is supplied as a molecular beam to a growth substrate by an appropriate means, and a molecular beam source consisting of a gas containing a group element is mixed with a decomposed monomer or a monomer by an appropriate means. - group compound semiconductor device, characterized in that a molecular beam of a mixture of molecules is supplied to the growth substrate, and the relative intensity of both the molecular beams is appropriately changed to form an epitaxial layer having a stoichiometric composition. manufacturing method.