JPS58219731A - Vapor growth method for compound semiconductor - Google Patents

Abstract

PURPOSE:To perform the vapor growth wherein the variation of concentration of electrons, etc. at the interface region is steep by a method wherein the doping gas is supplied to a fixed temperature, and thereafter the main raw material gas which contains the gas of organic metal is supplied, resulting in vapor growth. CONSTITUTION:The main raw material gas is obtained by mixing the carrier gas in the vessel 103 with the gas in the vessels 101 and 104. When an active layer 202 of a required concentration is formed on a crystal substrate 201 placed in a reaction furnace 106, first the doping gas in the vessel 108 is supplied into the reaction furnace 106, and thus the concentration of the doping gas in the reaction furnace 106 is kept at a constant value. Thereafter, vapor growth is performed by starting the supply of the main raw material gas, and accordingly the active layer 202 of a required concentration is formed. The use of such a method enables to prevent the decrease of the electron concentration at the interface between the substrate crystal and the active layer by a method wherein the doping gas deposits on the internal wall, etc. of a piping member 111.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a vapor phase growth method for compound semiconductors.

In particular, the present invention relates to a method of vapor phase growth of compound semiconductors in which growth is performed so as to steeply change the concentration of electrons or holes at the interface region between a crystal substrate and a vapor phase grown active layer.

[Technical background of the invention and its problems]

For example, GaAs electric field valve transistor GaAs
In manufacturing a microwave device such as a MESFBT, a GaAa active layer grown on a GaAs crystal substrate by a vapor phase growth method or a liquid phase growth method is used.

What is the charge concentration or hole concentration in such a GaAs active layer?

It usually depends on the element to which it is applied. Therefore, in order to obtain an active layer with a desired electron or hole concentration by vapor phase growth, a gas containing impurities must be intentionally mixed into the main raw material gas containing Ga or As. No.

In this case, in order to grow the n-type active layer, hydrogen sulfide (H,S) containing sulfur ts, a group Ⅰ element, is used.

Silane (SIH, ) containing silicon (Si), a group element.

Further, in order to grow a p-type active layer, an organic metal compound such as diethylzinc (Zp(CzHs)t) containing zinc (Zn), which is a group Ⅰ element, is used as an impurity doping gas. N is used as a so-called doping gas.

When doping a Ga As active layer using these doping gases, for example, in a thermal decomposition method using an organic Ga compound, a growth apparatus system as schematically shown in FIG. 1 is generally used. That is, the deposition of the GaAs layer is
The vapor of trimethyl gallium ((CH3)3Ga) (102) in the stainless steel storage container (101).

A s supplied from the A s H3 storage container (103)
H3 gas and hydrogen (H2) storage container (104)
The H2 gas containing the main raw material is mixed with the H2 gas supplied from the H2 gas and used as a carrier gas.
5) into the reactor (106), and then onto the crystal substrate (107). In such a growth system, for example, when depositing an n-type GaAs active layer having a desired electron concentration on a crystal substrate (107) placed in a reactor (106) by doping with sulfur (81), sulfur Supplied from the hydrogen gas storage container (108), the flow meter (109)
), H and S gases adjusted to predetermined flow rates are added to H and carrier gas in the gas mixer (110). For example, as shown in Fig. 2, semi-insulating Ga
A s crystal substrate (201) is doped with S to a thickness of 0.5
n-type Ga with μm electron concentration I X I Q”c+n-3
When forming the As active layer (202), H,
The addition of S gas to the H2 carrier gas was performed in the active layer (20
2) is done just before the growth starts.

However, in such a conventional doping method, immediately after mixing H and S into the H and carrier gas, the H and S concentrations in the H and carrier gas introduced into the reactor (106) are
, 8 gas inlet (105) from gas storage container (108)
The inner wall of the piping member (111) or the reactor (10
6) Temporarily decreases due to adsorption of H and S on the inner walls, etc. This is mainly due to the semi-insulating substrate crystal (2
01) and the active layer (202), the steep decrease in electron concentration near the interface (203) is impaired.

The curve (300) in FIG. 3 is the electron concentration distribution near the interface obtained in this case, and has a gentle appearance. When applied to the fabrication of an ebitaxial Unihara G a As field effect transistor in which the electron concentration in the active layer gradually decreases near the interface, the device characteristics, especially the current -
The voltage characteristics become poor as shown in FIG. 4, resulting in deterioration of so-called pinch-off characteristics and a decrease in mutual conductance, which significantly hinders the production of field effect transistors. Therefore, in manufacturing field effect transistors where a rapid decrease in electron concentration near the interface is essential, a doping method that can change the steep electron concentration slope at the interface between the substrate crystal and the active layer is required. It becomes necessary.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks and provides a method for vapor phase growth of a compound semiconductor in which the compound semiconductor is grown in vapor phase so as to steepen the electron concentration gradient at the interface between the substrate crystal and the vapor phase grown active layer.

[Summary of the invention]

That is, this invention is a compound semiconductor vapor phase growth method that utilizes thermal decomposition of an organic metal and adds impurities by doping, in which a doping gas is continuously supplied into a reactor until the concentration reaches a steady value, The present invention is a method for vapor phase growth of a compound semiconductor, in which the supply of a main raw material gas containing an organometallic gas is started after reaching a steady state value, and vapor phase growth is performed while simultaneously feeding the main raw material gas.

According to this invention, it is possible to prevent the loss of doping gas due to adsorption on piping members or the inner wall of the reactor that occurs in the early stage of growth, and to prevent the impurity concentration from rapidly increasing at the interface between the substrate crystal and the deposited layer. You can change the degree. G
This is an excellent method for adding impurities to a Jl-V group compound semiconductor growth layer.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In this example, first, sulfur (81) is doped to give an electron concentration of I
( ) a As active layer of semi-insulating Ga As
A case will be described in which an epitaxial wafer for a field effect transistor is formed directly on a crystal substrate. The active layer is formed using a pyrolysis vapor phase growth apparatus shown in FIG. 1, which uses arsine and trimethylgallium as main raw materials. The doping gas is hydrogen sulfide (HxS) gas diluted with hydrogen (Hl). Also, 1lllf of H,8 gas is approximately 30 ppm.

The piping from the H, S gas storage container (108) to the gas inlet (105) on the reactor (106) has an inner diameter of approximately 6.
A stainless steel pipe made by our company is used, and the length of this stainless steel pipe from the H.8 gas storage container (108) to the gas inlet (105) is about 4 lengths. The deposition of the Ga As growth layer is carried out from the H, gas storage container (104) to the reactor (10
6) H and carrier gas flow rate supplied to 6.71
/f+, arsine gas, but the arsine gas flow rate supplied from the storage container (103) diluted with hydrogen at a concentration of 10.6% is 217 cc/min, and the H2 flow rate to bubble the trimethyl gallium (102) held in Ooo is 31 cc/min. and the substrate temperature was set at 660°C. Under these flow rate and substrate temperature conditions, the above electron concentration I
To form an active layer of 10"α-3, H and S residues at the above concentration are heated in a reactor (106 cc) at a rate of 120 cc/min.
) must be introduced. However, when the H, S gas flow rate introduced into the reactor (106) is 120 cc/min, in order for the concentration of the H1S gas introduced into one reactor to reach a steady state, the H,8 gas must be replaced with the H, carrier gas. mixer (110
) for at least 10 minutes after attachment.

Therefore, in this example, only H, 8 gas is flowed for 10 minutes in advance, and then raw material gas is fed together. Therefore, the cocks (112) and (113) are opened at this point. The depth direction electron concentration profile (500) of the substrate crystal deposited layer formed under these conditions is as shown in FIG.
When compared to the curve (300) in the figure, the electron concentration changes rapidly at the interface between the substrate crystal and the active layer. In this way, it is possible to grow a GaAs epitaxial wafer having a steep electron concentration profile. Furthermore, when a field effect transistor with a gate length of 1.0 μm, for example, is fabricated using an 0aAs epitaxial wafer exhibiting such a steep electron concentration profile, a good current-voltage characteristic curve is obtained, as shown in the current-voltage characteristic curve diagram in Figure 6. When compared with the field-effect transistor characteristics shown in Figure 4 for a device manufactured using an epitaxial wafer with pinch-off and the electron concentration near the interface shown in Figure 3, the mutual conductance is improved by about twice. Ru. -Also, as shown in Figure 2, Ga
Instead of depositing the active layer directly on the A S crystal substrate, as shown in FIG.
5 μm, electron concentration 1×1017 degrees 1S doped Ga
When an epitaxial wafer having a structure in which an undoped GaAs buffer layer (704) with a thickness of 277 m is inserted between the As active layer (702) and the above buffer layer ( 704) and active layer (7
The electron concentration profile near the interface (703) with 02) is shown in FIG. 8 (SOO). Note that the electron concentration profile (801) shown in the same figure is related to a comparative example of the type in which the epitaxial wafer is formed in the same manner as the epitaxial wafer related to the curve (300) in FIG. 3, and a buffer layer is provided. It can be seen from the profile (801) in FIG. 8 that in the conventional doping method, the electron concentration changes slowly near the interface (703) and a steep electron concentration profile cannot be obtained.

However, when the doping method according to the present invention is adopted, the epitaxial wafer 1 shown in FIGS.
It is clear from the electron concentration profiles shown in FIGS. 5 and 8 that a sharp change in electron concentration is obtained near the interface regardless of the difference in structure.

In the above embodiment, the GaAs epitaxial active layer is formed on the GaAs crystal substrate by doping S, but the method of the present invention is to form the GaAs epitaxial active layer on the GaAs crystal substrate by the thermal decomposition method. GaA by adding impurities
Not only when forming the s active layer, but also when forming other t-V1! fc
The present invention can also be applied to the formation of an active layer made of an m-v group semiconductor such as GaAs or InP doped with impurities by a % rogen vapor phase epitaxy method on a semiconductor crystal, for example, an InP crystal substrate. The impurity is not limited to S, and when forming the n-type growth layer, group II elements such as Si, or Se
, Te, etc., or when forming the p-type growth layer, a group (1) element such as Zn may be used.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to rapidly change the electron concentration at the interface between the active layer and the substrate crystal or at the interface between the buffer layer and the active layer. Furthermore, epitaxial wafers for field effect transistors, which require a constant electron concentration in a relatively thin active layer and a rapid change in electron concentration near the interface, can be obtained with high yield by adopting this invention. This can contribute to improving the productivity of field effect transistors with good characteristics.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a growth apparatus used in the pyrolytic vapor phase growth method using organic Ga compounds, Figure 2 is a cross-sectional view of an epitaxial wafer with an active layer formed on a GaAs substrate, and Figure 3
The figure shows the electron concentration profile in the sulfur (8)-doped GaAs active layer obtained when an epitaxial wafer with the structure shown in Figure 2 is created using a conventional doping method.
Figure 4 shows G having the electron concentration profile shown in Figure 3.
Drain current-voltage characteristics diagram of a GaAs field effect transistor fabricated using aAs active layer, Figure 5 shows an electron concentration of I
Figure 6 shows the electron concentration profile in the active layer when the doped active layer is formed by the conventional method and the method of the present invention. An example of drain current-voltage characteristics obtained when a GaAs field effect transistor is created using the layer. Figure 7 shows a buffer layer and GaA on a GaAs substrate crystal.
s A cross-sectional view of an epitaxial wafer on which an active layer is formed. FIG. 8 is a diagram showing the electron concentration profile in an epitaxial wafer having the structure shown in FIG. 7, prepared by the conventional method or the method of the present invention. In Figure 1, (101)...Stainless steel storage container for storing trimethyl gallium (102)...Trimethyl gallium (103)...Arsine gas storage container (104)...Hydrogen gas storage container (105)...Gas Inlet (106)...Reactor (107)...Substrate crystal (108)...Hydrogen sulfide gas storage container (109)...
Flow meter (110)...Gas mixer (111)...Piping members (201) in Figure 2 -GaAs substrate crystal (202) -GaAs active layer (203)...Boast crystal and active layer Interfaces in Figures 3 and 5 (300)... Electron concentration profile of the active layer obtained when sulfur doping is performed based on the conventional method Figure 5 shows (500)... Sulfur doping is performed according to the present invention In Figure 7, the electron concentration profile of the active layer obtained when the method is carried out is as follows: (701)=GaAs crystal substrate (702)...Active layer (703)...Interface between buffer layer and active layer (704)・
・Buffer layer (801) in FIG. 8... Electron concentration profile at the buffer layer and active layer interface obtained by the conventional method (800)... The buffer layer and active layer interface achieved by the method of the present invention An example of an electron concentration profile Agent Patent attorney Inoue - Male Figure 1 Traci 97 [Z Rainbow (V]□

Claims (1)

[Claims] In a compound semiconductor vapor phase growth method that utilizes thermal decomposition of an organic metal and adds impurities to a growth layer by doping, a doping gas is introduced into a reactor in advance until the concentration reaches a steady value. Continue to supply. A method for vapor phase growth of a compound semiconductor, which is characterized in that after reaching a steady state value, the supply of a main raw material gas containing organometallic scum is started and the vapor phase growth is performed while simultaneously feeding the main raw material gas.