JP2889291B2 - Method for manufacturing p-type semiconductors of group III-V - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to, for example, III-type InGaAs semiconductors.
The present invention relates to a method for manufacturing a group V compound p-type semiconductor.

[Prior art]

For example, when manufacturing a p-type InGaAs photocathode which is a semiconductor photocathode, as a means for increasing the emission efficiency of free electrons, a method of forming an internal gradient of potential energy,
Further, a method is known in which the doping amount of the doping material is changed between the substrate side and the free electron emission surface side, and an internal electric field is formed by the concentration gradient of the doping amount. These methods have been practiced separately and independently in a single photocathode. As a method of forming the internal gradient of the potential energy as described above, there is a method of controlling the supply ratio of In and Ga. As a method of forming the concentration gradient of the doping amount, a method of controlling the supply amount of the doping material has been adopted.

[Problems to be solved by the invention]

The conventional method as described above uses a combination of the internal gradient of the potential energy and the concentration gradient of the doping amount,
The doping amount must be controlled for each active layer having a different energy gap, and the active layer growth process is complicated, and it is difficult to determine the growth conditions. This is a common problem not only in the photocathode but also in the group III-V compound p-type semiconductor. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is intended to make it easy to simultaneously form the gradient of the potential energy inside the active layer and the gradient of the concentration of the dopant in the active layer. The present invention relates to a method for manufacturing a mold semiconductor.

[Means for Solving the Problems]

According to the present invention, a p-type III
When forming the group-V layer, the concentration gradient of the doping amount in the group-III-V active layer is reduced by keeping the gaseous phase ratio of the group-III raw material constant, changing the flow rate of zinc as a doping material, and changing only the flow rate thereof. The object is achieved by simultaneously forming the gradient of the composition ratio of the group element. Further, the above object is achieved by keeping the gaseous phase ratio of the group III raw material constant and changing only the flow rate of the doping material. Further, the above object can be achieved by using InGaAs as the III-V group compound. Further, the composition of the active layer in InxGa ₁ -xAs is 0 ≦ x ≦ 0.2
By setting 5, the above object is achieved. Further, the above object is achieved by setting the doping amount of the doping material to 10 ¹⁸ to 10 ²¹ cm ^-3 . According to the present invention, when forming a p-type III-V group layer by MOCVD growth, the concentration gradient of the doping amount and the internal gradient of the potential energy in the III-V group active layer can be simultaneously and easily controlled by using zinc as a doping material. It is based on the knowledge that this can be achieved. In particular, when the gaseous phase ratio of the group III raw material was fixed, the internal gradient of the potential energy and the concentration gradient of the doping amount could be easily achieved by changing only the flow rate of the doping material. Further, when the III-V group compound was InGaAs and the doping material was zinc, the above tendency was more remarkable. Furthermore, in the above case, when the composition of the active layer in InxGa ₁ -xAs is 0 ≦ x ≦ 0.25, it is easy to form an internal gradient of potential energy and a concentration gradient of doping amount.

【Example】

Hereinafter, the present invention will be described in detail with reference to the drawings showing an apparatus and a manufacturing process for carrying out the present invention. This embodiment relates to a case where a p-type InGaAs layer is formed on a GaAs substrate when forming an InGaAs single crystal film for forming a semiconductor photocathode. As shown in FIG. 1, a sliced GaAs substrate 14 is placed on a carbon susceptor 12 in a reaction tube 10. The growth of InGaAs on the GaAs substrate 14 is performed by the MOCVD growth method. In this case, as a group III raw material, trimethylgallium (hereinafter, TMG) and triethylindium (hereinafter, TEI) are used.
Arsine (hereinafter, AsH ₃ ) as a V-group raw material, and diethyl zinc (hereinafter, DEZ) as a doping material are used on an H ₂ basis. The TMG is supplied from the TMG cylinder 16, the TEI is supplied from the TEI cylinder 18, and the DEZ is supplied from the DEZ cylinder 20 to the reaction tube 10 via the mass flow meter 22. AsH ₃ and H ₂ are supplied from respective supply sources (not shown). Generally, in the case of a p-type semiconductor, the gas phase ratio χv = TMG / TMG + T
When the EI was kept constant at, for example, 0.863 and the flow rate of DEZ was controlled as shown in Table 1 below, the doping amount and the composition ratio were as shown in the right column of Table 1. When this is applied to the manufacture of the semiconductor photocathode 28 shown in FIG. 2, a buffer layer 24 of p-type In _0.08 Ga _0.92 As is grown on the GaAs substrate 14 by 10 to 15 μm. The active layer 26 is grown thereon by keeping the gas phase ratio Δv constant and gradually reducing the flow rate of DEZ from the substrate side to the vacuum side to 3 μm. As a result, in the active layer 26, the doping amount is
The concentration gradually decreases to 1 × 10 ²⁰ cm ^-3 on the substrate side and 2 × 10 ¹⁹ cm ^-3 on the vacuum side, and the composition ratio x is 16% on the substrate side and 16% on the vacuum side.
It gradually increased to 20%. That is, in the normal case, the composition ratio is changed by changing the gas phase ratio, and the doping amount is controlled by changing the flow rate of DEZ. By changing only the flow rate, as described above, the concentration gradient of the doping amount and the gradient of the composition ratio, that is, the internal gradient of the potential energy could be simultaneously achieved. In other words, in the growth of p-type InGaAs, by gradually decreasing the supply amount of DEZ, the concentration gradient in which the doping amount decreases temporarily from the substrate side to the electron emission surface side, and the band in which the composition ratio x increases in the opposite direction temporarily increase. The gap inclination was achieved at the same time. A similar tendency is observed when the composition ratio Δv is different or when DEZ
Was confirmed even under different flow rates. The energy band diagram (energy level diagram) of the p-type InGaAs photocathode obtained as described above is as shown in FIG. In the figure, A indicates a conduction band, B indicates a valence band, C indicates a Fermi level, D indicates a cesium oxide layer, and E indicates a vacuum level. From this figure, it is clear that there is an internal gradient of potential energy due to both the action of the band gap gradient and the doping amount gradient, which enhances the free electron emission efficiency. Although the above embodiment is directed to the process of manufacturing a p-type InGaAs photoelectric surface, the present invention is not limited to this, and can be applied generally to the manufacture of III-V group p-type semiconductors. It is. Therefore, for example, P may be used instead of As.

【The invention's effect】

Since the present invention is configured as described above, it has an excellent effect that both the band gap gradient and the dope amount gradient can be easily and simultaneously formed only by controlling the flow rate of the dope material.

[Brief description of the drawings]

FIG. 1 is a piping diagram showing a MOCVD apparatus for carrying out a method for producing a group III-V compound p-type semiconductor according to the present invention.
FIG. 3 is a cross-sectional view showing a photocathode prepared by the same manufacturing method, and FIG. 3 is an energy band diagram of the photocathode. 10 ... Reaction tube, 14 ... GaAs substrate, 16 ... TMG cylinder, 18 ... TEI cylinder, 20 ... DEZ cylinder, 22 ... Mass flow meter, 24 ... Buffer layer, 26A ... First layer, 26B ... 2nd layer, 26C ... 3rd layer, 28 ... Photocathode.

Claims (4)

(57) [Claims] 1. A p-type III-type film is formed on a substrate by MOCVD growth.
When forming the group V layer, the concentration gradient of the doping amount in the group III-V active layer is increased by keeping the gaseous phase ratio of the group III raw material constant and changing only the flow rate using zinc as a doping material. A method for producing a group III-V compound p-type semiconductor, characterized by simultaneously forming a gradient of a composition ratio of elements. 2. The method according to claim 1, wherein said III-V compound is InGaAs. 3. The composition according to claim 2, wherein the composition of the active layer in InxGa ₁ -xAs is 0 ≦ x ≦ 0.25.
A method for producing an IV group compound p-type semiconductor. 4. A method for producing a group III-V compound p-type semiconductor according to claim 1, wherein the doping amount of the doping material is 10 ¹⁸ to 10 ²¹ cm ^-3. .