RU2569042C1 - Production of heterostructure for translucent photocathode - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: claimed heterostructure for translucent photocathode of Ga arsenide by MOS-hydride epitaxy. Here locking ply and active region are grown at 600-640°C. Additionally, this structure includes transition ply of composition varying from p-GaAs to p-Al_yGa_1-yAs. Note that at growing the temperature is increased to 700-760°C. Buffer ply is grown on said transition ply at 700-760°C. Ply growth rate makes from 0.1 to 3 mcm/hour. Metalorganic zinc compound flow is selected to ensure the required concentration of acceptor dopant in grown plies.

EFFECT: higher quantum efficiency of photocathode.

3 cl, 1 dwg

Description

Technical field

The invention relates to the field of manufacturing technology of semiconductor materials and devices by gas-phase epitaxy using organometallic compounds, in particular to the manufacture of a photosensitive element of optoelectronic devices, namely, the technology of growing a heterostructure for a semiconductor translucent photocathode with an active layer of gallium arsenide, photosensitive in visible and near infrared range.

State of the art

A known method of manufacturing a heterostructure of a semiconductor translucent photocathode of gallium arsenide by liquid phase epitaxy [I.V. Pinchuk, Development of semiconductor materials for night-time monitoring devices and industrial technology for their production, The dissertation for the degree of candidate of technical sciences, Moscow, 2001]. The disadvantage of this method is the low productivity and high density of crystalline defects of the heterostructure.

A known method of manufacturing a heterostructure of a semiconductor translucent photocathode from gallium arsenide by molecular beam epitaxy. The disadvantage of this method is the low productivity [I. Sakhno, A.V. Dolgikh, V.G. Chubarev, I.I. Marakhovka, Yu.G. Galitsyn, V.G. Mansurov, A.S. Suranov, Letters in ZhTF, 1996, volume 22, issue 23].

Closest to the proposed method for the totality of existing features is a method of manufacturing a heterostructure of a semiconductor semitransparent photocathode from gallium arsenide by the method of MOS hydride epitaxy [patent US 6597112 B1, 07/22/2003, H01J 40/06]. The disadvantage of this method is that the active layer of the photocathode heterostructure, which is zinc doped with gallium arsenide with a concentration of acceptor impurity atoms of at least 5 · 10 ¹⁸ cm ^-3 , is grown at temperatures above 650 ° C. Such temperatures are characterized by strong desorption of zinc atoms from the surface of the growing epitaxial layer, which causes a deterioration in the crystal perfection of the material of the active layer with a concomitant decrease in the diffusion length and recombination rate of minority charge carriers. This leads to a deterioration in the quantum efficiency and integrated sensitivity of the photocathode made from the heterostructure obtained in this way.

Disclosure of invention

The technical result of the invention is to increase the integrated sensitivity and quantum efficiency of a semiconductor translucent photocathode operating in the "transparency" mode, based on a heterostructure with an active layer of gallium arsenide obtained by the proposed method, by reducing the likelihood of misfit dislocations in the transition and buffer layers of the heterostructure, removal of the potential barrier for minority charge carriers at the boundary of the active and transition layers and, therefore, with izheniya recombination rate of minority charge carriers at the interface between the active and buffer layers.

In accordance with the invention, the technical result is achieved by the fact that a method for producing a heterostructure for a translucent photocathode by the MOS hydride epitaxy method is proposed, which includes selecting a gallium arsenide substrate, heating it in a hydrogen stream from room temperature to a temperature of 600 ° C-640 ° C, growing at that the same temperature of the substrate of the p-Al _x Ga _1-x As retaining layer with a concentration of zinc impurity and on it the growth of an active p-GaAs layer with a concentration of P ₂ zinc impurity. Then, with an increase in the substrate temperature from 600 ° C – 640 ° C to 700 ° C – 760 ° C, a transition layer of variable composition from p-GaAs to p-Al _y Ga _1-y As is grown on the active layer. During the cultivation of the transition layer, starting from the surface adjacent to the active layer, the feed flow of the organometallic aluminum compound is gradually increased, providing an increase in the aluminum content in the transition layer to the value “y” on its next surface. Also, starting from the surface adjacent to the active layer, the feed flow of the organometallic zinc compound during the transition layer is gradually reduced to ensure that the zinc impurity concentration decreases from the value of P ₂ on the surface adjacent to the active layer to the value of P ₃ at its next surface. On it, further, at a substrate temperature of 700 ° C-760 ° C, a p-Al _y Ga _1-y As buffer layer with a concentration of P ₃ zinc impurities is grown. All layers of the heterostructure are grown at a growth rate of 0.1 to 3.0 μm / h.

A new and non-obvious set of features of a method for producing a heterostructure with an active layer of gallium arsenide is proposed, which can significantly increase the integral sensitivity and quantum efficiency of a semiconductor translucent photocathode operating in the "transparency" mode made of a heterostructure obtained by the proposed method. The p-Al _x Ga _1-x As retaining layer is grown from compounds containing arsenic and organometallic compounds of gallium, aluminum and zinc with streams providing an aluminum content “x” and a concentration of P ₁ zinc impurities in the retaining layer, the active layer p -GaAs from compounds containing arsenic and organometallic compounds of gallium and zinc with a stream providing a concentration of P ₂ zinc impurities in the active layer, a transition layer from compounds containing arsenic, and organometallic compounds of gallium, aluminum and zinc, as well as a buffer layer p Al _y g a _y-1 As from compounds containing arsenic, and organometallic compounds of gallium, aluminum and zinc with streams providing the aluminum content “y” and the concentration of P ₃ zinc impurities in the buffer layer.

Lowering the temperature of the substrate when growing the active layer below 600 ° C leads to the fact that the atoms of the elements falling from the gas phase onto the surface of the growing epitaxial layer do not have time to integrate into energetically favorable positions corresponding to the nodes of the crystal lattice. This worsens the crystalline perfection of the material of the active layer and causes a decrease in the diffusion length, an increase in the rate of recombination of minority charge carriers, and a deterioration in the characteristics of the photocathode. The enhanced desorption of zinc atoms from the surface of the growing epitaxial layer at substrate temperatures above 640 ° C also causes a deterioration in the crystalline perfection of the material of the active layer with similar consequences. The need for growth of the buffer layer at a substrate temperature of 700-760 ° C is explained by the significant aluminum content in it. The high affinity of aluminum atoms for oxygen leads to the formation of complexes that form deep levels and act as scattering centers, reducing the diffusion length and increasing the rate of recombination of minority charge carriers generated in the buffer layer upon exposure to light, and thus reducing the probability of diffusion of these carriers to the emitting surface of the photocathode. An increase in the temperature of growing a layer with a high aluminum content suppresses the incorporation of oxygen atoms and reduces the concentration of the mentioned complexes, which, in accordance with the above mechanism, leads to an increase in the quantum yield and integrated sensitivity of the photocathode. The retaining layer, despite an even higher aluminum content, is grown at a substrate temperature of 600-640 ° C, since it is subsequently removed and does not affect the operation of the photocathode.

The technical result is also achieved by the fact that when growing the transition layer, it provides a monotonically increasing and continuous content of aluminum “y” and a monotonously decreasing and continuous content of zinc, which further reduces the likelihood of misfit dislocations in the transition and buffer layers, eliminating the potential barrier for minority charge carriers at the boundary of the active and transition layers, lowering the rate of recombination of minority charge carriers at the boundary between the active and the transition single layers and, therefore, improving the characteristics of the photocathodes.

The technical result is achieved by the fact that a GaAs intermediate layer from 0.05 μm to 0.2 μm thick is grown between the substrate and the retainer layer at a substrate temperature of 600-640 ° C, which reduces the likelihood of misfit dislocations in the retainer and active layers during their growth and increase in sensitivity and quantum efficiency of the photocathode.

In addition, the technical result is achieved by the fact that:

- the substrate is selected n-type conductivity;

- the substrate is selected p-type conductivity;

- the substrate is selected i-type conductivity;

- in the buffer layer p-Al _y Ga _1-y As the content of "y" aluminum is selected from 0.4 to 0.7;

- the transition layer is selected with a thickness of 0.10 μm to 1.0 μm;

- the concentration of P ₂ zinc impurities in the active layer is selected from 5 · 10 ¹⁸ cm ^-3 to 1.5 · 10 ¹⁹ cm ^-3 ;

- the concentration of P ₃ zinc impurities in the buffer layer is selected from 1 · 10 ¹⁸ cm ^-3 to 3 · 10 ¹⁸ cm ^-3 .

We have not found the proposed combination of features of the invention, which confirms the presence of its novelty. In addition, the proposed method for producing a heterostructure of a translucent photocathode with an active layer of gallium arsenide contains an unobvious set of sequence of layers, temperatures of their growth, and the composition of the supplied reagents, which allows us to conclude that the proposal meets the criterion of "inventive step".

The technological implementation of the heterostructure of the translucent photocathode proposed in the present invention is based on well-known basic methods for the manufacture of semiconductor photocathodes, including translucent ones, which are currently well developed and widely used. The proposal meets the criterion of "industrial applicability".

Brief Description of the Drawings

The present invention is illustrated by the drawing in FIG. 1, which schematically shows the structure of a heterostructure for a semiconductor translucent photocathode with an active layer of gallium arsenide.

Embodiments of the invention

The invention is further explained by specific embodiments of the proposed method for producing a heterostructure for a translucent photocathode with an active layer of gallium arsenide (hereinafter referred to as “Heterostructure”). We further give a part of the variants of the method for producing a heterostructure from the totality of possible ones.

Example 1. The inventive method for manufacturing a heterostructure schematically depicted in FIG. 1, carried out by the method of MOS hydride epitaxy in several stages. The GaAs substrate 1 is selected with a thickness of 500 μm of n-type conductivity, it is heated in a high-purity hydrogen stream at a temperature of 620 ° C, then heterostructure layers are deposited on it sequentially by feeding trimethylaluminum and trimethylgallium vapor into the hydrogen channel as sources of aluminum, gallium, arsenic hydride as a source of arsenic, diethylzinc vapor as a source of acceptor impurities. All layers of the heterostructure are grown at a growth rate of 1.55 μm / h.

On the substrate 1 at its temperature of 620 ° C are grown:

- the stopper layer 2 p-Al _x Ga _1-x As, where the value of "x" is 0.7 with a concentration of P ₁ acceptor impurities equal to 2 · 10 ¹⁸ cm ^-3 and a thickness equal to 0.9 μm;

- active layer 3 p-GaAs with a concentration of P ₂ acceptor impurities equal to 1 · 10 ¹⁹ cm ^-3 , and a thickness equal to 2.0 μm.

Then produce a gradual rise in the temperature of the substrate 1 to 730 ° C with the simultaneous deposition of the transition layer 4, a thickness equal to 0.55 μm. The transition layer 4 is grown with a variable composition from p-GaAs (near the boundary with the active layer 3) to p-Al _y Ga _1-y As, where the "y" value is 0.55 (near the border with the next buffer layer 5) with a linear change in the magnitude of aluminum over the thickness of the layer, gradually increasing during its growth, the feed flow of the organometallic aluminum compound. In addition, the transition layer 4 is grown with a gradual decrease in the flow rate of the organometallic zinc compound during its growth to ensure a linear decrease in the concentration of zinc from P ₂ equal to 1 · 10 ¹⁹ cm ^-3 at the border with active layer 3, to P ₃ equal to 2 10 ¹⁸ cm ^-3 at the border with the buffer layer 5.

Then, at the same temperature of 730 ° C, a buffer layer of 5 p-Al _y Ga _1-y As is grown at “y” equal to 0.55, with a concentration of P ₃ acceptor impurity equal to 2 · 10 ¹⁸ cm ^-3 , and a thickness equal to 0.55 microns.

Technological patterns of growth of the transition layer depend on the type of organometallic compounds of aluminum, gallium and zinc, growth devices, etc., and in a known way the modes are calculated that ensure a linear increase in the aluminum content of pure gallium arsenide in the transition layer 4 (at the boundary with the active layer 3 ) to a value «y» (near the boundary with the buffer layer 5) and a linear decrease in the concentration of zinc from P ₂ at the boundary with the active layer 3 and P ₃ at the interface with the buffer layer 5. to calculate the costs of organometallic compounds, it is necessary s to obtain the desired layer composition and doping using known concentrations of correspondence tables streams and the heterostructures parameters.

After completion of the growth of the Heterostructure, the grown plates were transferred to the subsequent technological cycle of creating the photocathode element and its assembly. The following output parameters were obtained on fabricated translucent photocathodes:

- integrated sensitivity equal to 3190 μA / Lm and

- quantum efficiency at a wavelength of 700 nm, equal to 53%, which exceeds the known values by 1.2 times.

Example 2. In this case, the manufacturing method of the Heterostructure differed from Example 1 as follows (see Figure 1). A 300-μm n-type GaAs substrate 1 is selected, it is heated in a duct of high-purity hydrogen at a temperature of 600 ° C, then at this temperature a retaining layer of 2 p-Al _x Ga _1-x As is grown on it, where the value is “x” equal to 0.5 with the concentration of the acceptor impurity equal to 1 · 10 ¹⁸ cm ^-3 and a thickness equal to 0.1 μm, and the active layer 3 p-GaAs with a concentration of P ₂ acceptor impurity equal to 5 · 10 ¹⁸ cm ^-3 , and a thickness equal to 1.0 μm.

A gradual increase in the substrate temperature 1 to 700 ° C is performed simultaneously with the deposition of a p-type transition layer 4 of variable composition from p-GaAs (near the boundary with active layer 3) to p-Al _y Ga _1-y As, where the value of “y” is 0.4 (near the border with the next buffer layer 5), as well as with a linear decrease in zinc concentration from P ₂ equal to 5 · 10 ¹⁸ cm ^-3 at the border with active layer 3, to P ₃ equal to 1 · 10 ¹⁸ cm ^{- 3} at the boundary with the buffer layer 5. The layer thickness is 0.1 μm.

On the transition layer 4, further at the same temperature of 700 ° C, a buffer layer 5 p-Al _y Ga _1-y As is grown, with a “y” value of 0.4, with a concentration of P ₃ acceptor impurity equal to 1 · 10 ¹⁸ cm ^-3 , and a thickness equal to 0.1 μm. All layers of the heterostructure are grown at a growth rate of 0.1 μm / hour.

After completion of the growth of the heterostructure, the grown plates were transferred to the subsequent technological cycle of creating the photocathode element and its assembly. The following output parameters were obtained on fabricated translucent photocathodes:

- integral sensitivity equal to 2860 μA / Lm, and

- quantum efficiency at a wavelength of 700 nm, equal to 47%.

Example 3. In this case, the manufacturing method of the Heterostructure differed from Example 1 as follows (see Fig. 1). A 1 GaAs substrate with a thickness of 700 μm of n-type conductivity is selected, it is heated in a duct of high-purity hydrogen at a temperature of 640 ° C, then at this temperature a retaining layer 2 p-Al _x Ga _1-x As is grown on it, where the value is “x” equal to 0.9 with a concentration of P ₁ acceptor impurity equal to 3 · 10 ¹⁸ cm ^-3 and a thickness equal to 1.5 microns; and p-GaAs active layer 3 with an acceptor impurity concentration of P ₂ equal to 1.5 · 10 ¹⁹ cm ^-3 and a thickness of 3.0 μm.

A gradual rise in the substrate temperature 1 to 760 ° C is carried out simultaneously with the deposition of a p-type transition layer 4 of variable composition from p-GaAs (near the boundary with active layer 3) to p-Al _y Ga _1-y As, where the value of “y” is 0.7 (near the border with the next buffer layer 5), as well as with a linear decrease in zinc concentration from P2 equal to 1.5 · 10 ¹⁹ cm ^-3 at the border with active layer 3, to P ₃ equal to 3 · 10 ¹⁸ cm ^-3 at the boundary with the buffer layer 5. The layer thickness is 1.0 μm.

On the transition layer 4, further, at the same temperature of 760 ° C, a buffer layer 5 of p-Al _y Ga _1-y As is grown with a value of "y" equal to 0.7, with a concentration of P _{3 of the} acceptor impurity equal to 3 · 10 ¹⁸ cm ^-3 , and a thickness equal to 1.0 μm. All layers of the heterostructure are grown at a growth rate of 3.0 μm / h.

After completion of the growth of the heterostructure, the grown plates were transferred to the subsequent technological cycle of creating the photocathode element and its assembly. The following output parameters were obtained on fabricated translucent photocathodes:

- integrated sensitivity equal to 3100 μA / Lm, and

- quantum efficiency at a wavelength of 700 nm, equal to 51%.

The next variant of the proposed method differs from the first in that it uses a substrate of gallium arsenide of i-type conductivity.

The next variant of the proposed method differs from the first in that a p-type gallium arsenide substrate is used.

The next variant of the proposed method differs from the first variant in that before the deposition of the stopper layer on the gallium arsenide substrate after it is heated to a temperature of 620 ° C, a layer of undoped gallium arsenide, called an intermediate layer, with a thickness of 0.125 ± 0.025 μm, is pre-deposited by feeding hydrogen into the duct trimethylgallium vapor as a source of gallium; arsenic hydride as a source of arsenic.

For the considered three last variants of the method for manufacturing a heterostructure for a translucent photocathode, changes in the output parameters are noted at the level of measurement error.

Using the proposed method for manufacturing a photoemissive structure for a semiconductor translucent photocathode from gallium arsenide, photocathodes with an increased minimum of 10% quantum efficiency are obtained. The obtained values of the integrated sensitivity exceed 2500 μA / Lm, the integrated sensitivity is increased above 2500 μA / Lm

Industrial applicability

The invention can be used in the manufacture of a photosensitive element of optoelectronic devices: electron-optical converters and photomultipliers used in radiation detectors.

Claims (3)

1. A method of manufacturing a heterostructure for a translucent photocathode by MOS hydride epitaxy, comprising selecting a gallium arsenide substrate, heating it in a hydrogen stream from room temperature to a temperature of 600 ° C-640 ° C, growing the p-Al _x stop layer at the same temperature Ga _1-x As with a concentration of P ₁ zinc impurities; on it, growing an active p-GaAs layer with a concentration of P ₂ zinc impurities; then, when the substrate temperature is increased from 600 ° C-640 ° C to 700 ° C-760 ° C, growing on active layer of the transition layer, variable composition from p-GaAs to p-Al _y G a _1-y As, starting from the surface adjacent to the active layer, by gradually increasing the flow of organometallic aluminum compounds during the growth of the transition layer, providing an increase in the aluminum content in the transition layer to the value “y” on its next surface, and gradually reducing the flow supplying an organometal compound of zinc during growth of the transition layer to provide therein a zinc impurity concentration reduction of the value of P ₂ on the surface bordering the active layer to greatness us P ₃ at the next surface on which further at a substrate temperature of 700 ° C-760 ° C is grown a buffer layer of p-Al _y Ga _1-y As with the concentration of P ₃ zinc impurities, wherein all the layers are grown at a growth rate of 0, 1 to 3.0 μm / hour. 2. The method according to p. 1, characterized in that when growing the transition layer provide it monotonically increasing and continuous aluminum content and monotonically decreasing and continuous zinc content. 3. The method according to p. 1, characterized in that between the substrate and the retaining layer is grown an intermediate layer of GaAs with a thickness of 0.05 μm to 0.2 μm at a substrate temperature of 600-640 ° C.

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