RU2791961C1 - Method for manufacturing laser photoelectric converter - Google Patents

Abstract

FIELD: photoelectric laser radiation converters.

SUBSTANCE: method for manufacturing a photoelectric laser radiation converter includes growing an n-InGaAsP base layer, a p+-InGaAsP layer by liquid-phase epitaxy in a stream of purified hydrogen on an n-InP substrate, forming a diffusion p-n junction, thinning the InP substrate, forming front and rear ohmic contacts, etching of the separating mesa. In this case, undoped semiconductor materials InP, InAs, and GaAs are used as sources of components for the melt.

EFFECT: method makes it possible to obtain a gradient p-n junction with a controlled depth and doping profile in a single technological process with the growth of epitaxial layers of the heterostructure, which ensure the photosensitivity of the photoconverter in the wavelength range of 1.06-1.55 μm.

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Description

The invention relates to wireless power transmission systems, in particular, to a method for manufacturing photoelectric converters (PVC), and can be used in the electronics industry for converting laser radiation into electrical energy.

Systems for energy transmission along a laser beam based on a solar cell of monochromatic radiation with a wavelength of λ=1.06-1.55 μm are very promising due to their high efficiency. A promising material for creating solar cells operating in the indicated wavelength range is the InGaAs(P)/InP heterostructure.

A known method of manufacturing a photoelectric converter of laser radiation (see RU2318272, IPC H01L 31/18, published February 27, 2008), which consists in the fact that the epitaxial plate n-InP/n-InGaAs/n ⁺ -InP is covered with a film of silicon nitride with a frontal and back side. The windows for diffusion are opened from the side of the n-InP/n-InGaAs epitaxial layers and marks are formed for further alignment of the photomask patterns from the side of the n ⁺ -InP substrate. In n-InP/n-InGaAs epitaxial layers, a local pn junction is formed by cadmium diffusion. The n-InP/InGaAs/n ⁺ -InP wafer is covered with a second layer of a silicon nitride film on the side of the n-InP/n-InGaAs epitaxial layers, contact windows are opened in the second layer of the silicon nitride film, and ohmic contacts of gold with a titanium sublayer are created to p ⁺ - regions. In the silicon nitride film, on the side of the n ⁺ -InP substrate, windows are opened under contact with the n ⁺ -InP region, while a silicon nitride film remains above the region of p-n junctions, which serves as an antireflection coating. Gold is deposited with a titanium sublayer, so that a metallization is formed for contact with the n ⁺ -InP substrate, a pattern is etched in the gold film with a titanium sublayer, which on the one hand is a contact and provides ohmic contact to the n ⁺ InP substrate, and on the other hand forms a diaphragm , limiting the area of illumination only by the area of the space charge of the multielement photodetector.

The disadvantage of the known method of manufacturing a photoelectric converter of laser radiation is the complexity of the technological route when forming a p-n junction by diffusion through additional masks, as well as an increase in surface recombination and heterostructure defects.

A known method of manufacturing a photoelectric converter of laser radiation (see application WO2014027092, IPC H01L 31/054, publ. 20.02.2014), including the sequential formation of a Bragg reflector, a barrier layer, an active region including an n-doped layer and p-doped In _y Ga _1-y AS _x P _1-xy layer, lattice-matched with the substrate, at x=0.948, 0.957, 0.965, 0.968, 0.972 or 0.976 and y=0.557, 0.553, 0.549, 0.547, 0.545 or 0.544, respectively, the formation of a wide-gap window, an antireflection coating. In this case, the conversion of electromagnetic radiation with a wavelength of 1.55 μm is carried out in the active region.

The disadvantage of the known method of manufacturing a photoelectric converter of laser radiation is the expensive method of forming a heterostructure using gas-phase epitaxy, which reduces the crystallographic perfection of the heterostructure. Also, during the epitaxial growth of a heterostructure from the gas phase, toxic components are used, for example, phosphine.

A known method of manufacturing a photoelectric converter of laser radiation based on epitaxial InGaAs/InP structures (see RU2530458, IPC H01L 31/18, publ. structures with a pin junction to the n ⁺ -InP substrate. In this case, a plurality of identical photoelectrically unconnected pin regions on a conductive base are formed by ion etching with argon ions with an energy of 1 keV and a current density of 0.2 mA/cm ² of p ⁺ -InGaAs, p-InP, n-InGaAs pin structures on an n ⁺ -InP substrate to the n ⁺ -InP substrate through the photoresist mask and finishing chemical etching.

A disadvantage of the known method for manufacturing a photoelectric laser radiation converter is the use of an expensive ion-beam mesa etching method, which leads to the formation of a damaged layer and to the formation of structural defects.

A known method of manufacturing a photoelectric converter of laser radiation (see US6821801, IPC H01L 21/00, publ. 11/23/2004), including sequential growth by the method of gas-phase epitaxy from organometallic compounds on an n-InP substrate of a multilayer heterostructure of the active region based on InGaAlAs, a layer of lining p -InP, p-InGaAs layer, formation of mesa by liquid chemical etching, cleaning the side surface of the mesa with a gas containing chlorine or other halogens, while the active region is formed with fewer crystal defects, low power consumption and high reliability, while preventing inhibition of active backgrowth region resulting from the oxidation of Al contained in the active region. The advantage of the method is lower power consumption and high reliability.

The disadvantage of the known method of manufacturing a photoelectric converter of laser radiation is the use of an expensive method of growing a heterostructure using gas-phase epitaxy from organometallic compounds, which reduces the crystallographic perfection of the heterostructure and increases the toxicity of the process.

The closest in technical essence and essential features to the present technical solution is a method for manufacturing a photoelectric converter of laser radiation, taken as a prototype (see N.M. Vakiv, S.I. Krukovsky, A.V. Sukach, V.V. Tetyorkin, I. A. Mrykhin, Y. S. Mikhashchuk, R. S. Krutovsky "Properties of p+-InP/n-InGaAsP/n-InP double heterojunctions fabricated by liquid-phase epitaxy", Technology and design in electronic equipment, 2012, No. 2). The prototype method includes growing by liquid-phase epitaxy in a stream of purified hydrogen on an n-InP substrate with (100) orientation of the n-InGaAsP base layer, at an epitaxy start temperature of 650°C, with a cooling rate of 0.8°C/min, a p-InP layer ( Zn), at an epitaxy start temperature of 680°С, with a cooling rate of 0.8°С/min, formation of front and rear ohmic contacts, etching of the separating mesa. While the prototype method may include growing an additional buffer layer of n-InP with a thickness of 1.5 μm. The heterostructures were grown by liquid-phase epitaxy of InGaAsP quaternary solid solutions (Eg = 1.17 eV) 3–4 µm thick on InP substrates. In the p+-InP/n-InGaAsP/n-InP epitaxial structure, the p-n junction was created by a heavily doped indium phosphide layer and an additional buffer layer, which reduces the doping of the n-type layer.

The disadvantage of the known prototype method for manufacturing a photoelectric laser radiation converter is the difficulty of controlling and reproducing the depth of p-n transition due to the fact that zinc diffusion occurs during epitaxial growth at a sufficiently high temperature (above 680 ° C), and enough zinc is used as a source of zinc. a thick (more than 1.5 μm) and highly doped p ⁺ -InP layer (a practically infinite source of acceptor impurity), as well as the possibility of mismatch defects at the metallurgical boundary when growing semiconductor layers of different compositions and the possibility of uncontrolled penetration of zinc deep into the n-layer due to this.

The objective of the present invention is to develop a method for manufacturing a photoelectric converter based on the InGaAsP/InP heterostructure, which would make it possible to obtain a gradient p-n junction with a controlled depth and doping profile in a single technological process with the growth of epitaxial layers of the heterostructure, which ensure the photosensitivity of the photoconverter in the wavelength range 1.06- 1.55 µm.

The problem is solved by the fact that the method of manufacturing a photoelectric laser radiation converter includes growing by liquid-phase epitaxy in a stream of purified hydrogen on an n-InP substrate with (100) orientation of the n-InGaAsP base layer at a temperature of (620-650) ° C, the formation of р-n transition, thinning of the substrate, formation of front and rear ohmic contacts, and etching of the separating mesa. What is new is that the n-InGaAsP base layer is grown at a cooling rate of (0.2-0.3)°C/min, a p ⁺ -InGaAsP (Zn) layer is grown on the base layer at a temperature of (600-620)°C, at a cooling rate (0.2-0.3)°С/min, with a thickness of not more than 0.5 μm, the formation of the p-n junction is carried out by Zn diffusion from the p ⁺ -InGaAsP (Zn) layer into the n-InGaAsP base layer at a temperature of (500-550)°С during (5-20) minutes, undoped semiconductor materials In, InAs and GaAs, pre-annealed at a temperature of (700-720) ° C for (1.5-2.0) hours, and n-InP doped to the level not less than (3-5)⋅10 ¹⁷ cm ^-3 .

An additional (5-10) µm thick n-InP buffer layer can be grown from a tin-indium melt at cooling rates of (0.3-0.5)°C/min.

The use of a quaternary InGaAsP solid solution up to 0.5 μm thick as a highly doped p ⁺ layer, which plays the role of a subcontact layer and a wide-gap window, and a decrease in the temperature and growth rate of the highly doped p ⁺ layer makes it possible to avoid uncontrolled diffusion of the dopant deep into the n-material during epitaxy.

The base layer of n-InGaAsP is simultaneously a buffer layer, which leads to a simplification of the technological cycle for growing a heterostructure.

Diffusion of zinc occurs from a limited source of the p ⁺ -layer, after the end of epitaxial growth (after removal of the substrate with the growing layer from under the melt). Due to this, the diffusion process occurs in a single technological process, but separately from the growth of the p ⁺ -layer at temperatures from 500°C to 550°C. As a result, it becomes possible to precisely control the depth of the diffusion layer. The formation of a diffusion p-n junction during epitaxy makes it possible to create a smooth gradient transition of a controlled depth with an increased collection coefficient due to an internal pulling field and without introducing an additional technological stage.

Epitaxial growth of an additional n-InP buffer layer (5–10) µm thick improves the quality of the substrate material. At a thickness of less than 5 μm, the quality of the substrate material decreases; a thickness of more than 10 μm is technologically impractical. At cooling rates less than 0.3°С/min and more than 0.5°С/min, the quality of the n-InP layer decreases.

Epitaxial growth of the n-InGaAsP base layer at temperatures below 620°С and above 650°С, with a cooling rate of less than 0.2°С/min and more than 0.3°С/min, leads to a decrease in the quality and a change in the composition of the layer.

Epitaxial growth of a p ⁺ -InGaAsP (Zn) layer at temperatures below 600°С and above 620°С, with a cooling rate of less than 0.2°С/min and more than 0.3°С/min, leads to a decrease in the quality and a change in the composition of the layer.

The method for manufacturing a photoelectric laser radiation converter includes several stages. The InGaAsP/InP heterostructure is grown by liquid-phase epitaxy in a hydrogen atmosphere in a slider-type graphite cassette from an indium melt. As a substrate, InP wafers of n-type conductivity with a crystallographic orientation of the working surface (100) are used. Undoped semiconductor materials InP, InAs and GaAs are used as sources of components for the melt, which are preliminarily annealed for (1.5–2.0) hours without phosphorus for better purification and homogenization of the components. Immediately before the start of the epitaxial process, the melt solutions of the grown epitaxial layers and the substrate are kept at a temperature of (680-700)°C for (40-60) minutes in a stream of purified hydrogen in a graphite cassette with a high content of phosphorus vapor. After that, the prepared substrate is loaded into the cassette, and a source of phosphorus is added to the melt. The growth temperature of quaternary InGaAsP solid solutions varies from 600°С to 650°С. In order to prevent erosion of the surface of indium phosphide under the influence of high temperatures due to the evaporation of phosphorus in the epitaxial process, an excess pressure of phosphorus vapor is created above the substrate. To do this, an additional cell with tin melt and indium phosphide is formed in the cassette, which does not contact directly with the substrate during epitaxy, but allows phosphorus vapor to flow to its surface. In addition, immediately before the beginning of the growth of heterostructure layers, the upper layer (≤20 μm) of the InP substrate is etched in an undersaturated tin melt. The growth of the n-InGaAsP base layer is carried out in the temperature range of 620-650°C, with a cooling rate of 0.2-0.3°C/min. The p ⁺ -InGaAsP layer is grown in the temperature range (600-620)°C, with a cooling rate of (0.2-0.3)°C/min. The diffusion process is carried out for (5-20) minutes, while a controlled formation of the p-n junction and its displacement from the metallurgical boundary of epitaxial growth occurs. Next, the InP substrate is thinned, front and rear ohmic contacts are formed, and a separating mesa is created.

Example 1 A photoelectric converter of laser radiation was manufactured in several stages. An InGaAsP/InP heterostructure was grown by liquid-phase epitaxy in a hydrogen atmosphere in a slider-type graphite cassette from an indium melt. An n-type InP plate with a crystallographic orientation of the working surface (100) was used as a substrate. Undoped semiconductor materials InP, InAs, and GaAs were used as sources of components for the melt. The semiconductor materials were annealed for 1.5 hours without phosphorus. The melt solutions of the grown epitaxial layers and the substrate were kept at a temperature of 680°C for 40 minutes in a stream of purified hydrogen in a graphite cassette with a high content of phosphorus vapor. A prepared substrate was loaded into the cassette, and a source of phosphorus was added to the melt. The top layer (15 μm) of the indium phosphide substrate was etched in an undersaturated tin melt. An n-InGaAsP base layer was grown at a temperature of 620°C, with a cooling rate of 0.3°C/min, and a thickness of 3 μm. A layer of p ⁺ -InGaAsP was grown at a temperature of 610°С, with a cooling rate of 0.3°С/min, with a thickness of 0.5 μm. The p-n junction was formed by carrying out the diffusion process for 5 min. Next, the InP substrate was thinned by liquid chemical etching. An ohmic contact of n-type conductivity based on Au(Ge)/Ni/Au layers and an ohmic contact of p-type conductivity based on Cr/Au layers have been formed. A separating mesa was formed by liquid chemical etching.

Example 2 A photoelectric laser light converter was manufactured by the method described in Example 1, with the following differences. Annealing of semiconductor materials was carried out for 2 hours without phosphorus. The melt solutions of the grown epitaxial layers and the substrate were kept at a temperature of 700°C for 60 minutes in a stream of purified hydrogen in a graphite cassette with a high content of phosphorus vapor. The top layer (20 μm) of the InP substrate was etched in an undersaturated tin melt. A base layer of n-InGaAsP was grown at a temperature of 650°С, with a cooling rate of 0.3°С/min, with a thickness of 5 μm. A layer of p-InGaAsP was grown at a temperature of 600°С, with a cooling rate of 0.2°С/min, with a thickness of 0.5 μm. The p-n transition was formed by carrying out the diffusion process for 20 minutes.

Example 3 A photoelectric laser light converter was manufactured by the method described in Example 1, with the following differences. Annealing of semiconductor materials was carried out for 1.7 hours without phosphorus. The melt solutions of the grown epitaxial layers and the substrate were kept at a temperature of 690°C for 50 minutes in a stream of purified hydrogen in a graphite cassette with a high content of phosphorus vapor. The top layer (10 μm) of the indium phosphide substrate was etched in an undersaturated tin melt. A base layer of n-InGaAsP was grown at a temperature of 630°C, with a cooling rate of 0.25°C/min for 10 minutes, with a thickness of 4 μm. A layer of p-InGaAsP was grown at a temperature of 620°С, with a cooling rate of 0.25°С/min, with a thickness of 0.5 μm. The p-n transition was formed by carrying out the diffusion process for 15 minutes.

The result of the technical solution was the manufacture of a photoelectric converter based on the InGaAsP/InP heterostructure with a gradient p-n junction with a controlled depth and doping profile, formed in a single technological process with the growth of epitaxial layers of the heterostructure. The photosensitivity of the manufactured photoconverters is in the wavelength range of 1.06-1.55 µm.

Claims (2)

1. A method for manufacturing a photoelectric laser radiation converter, including growing by liquid-phase epitaxy in a stream of purified hydrogen on an n-InP substrate with (100) orientation of the n-InGaAsP base layer at a temperature of 620-650°C, formation of a p-n junction, thinning of the substrate , the formation of front and rear ohmic contacts and etching of the separating mesa, characterized in that the base layer of n-InGaAsP is grown at a cooling rate of 0.2-0.3 ° C / min, a layer of p ⁺ -InGaAsP (Zn) is grown on the base layer, at a temperature of 600- 620°С, with a cooling rate of 0.2-0.3°С/min, with a thickness of not more than 0.5 μm, the p-n junction is formed by diffusion of Zn from the p ⁺ -InGaAsP (Zn) layer into the n-InGaAsP base layer at a temperature of 500-550 °C for 5–20 min, and undoped In, InAs, and GaAs, preliminarily annealed at a temperature of 700–720°C for 1.5–2.0 h, and n-InP doped to a level of at least 3-5⋅10 ¹⁷ cm ^-3 . 2. Method according to claim 1, characterized in that a 5-10 µm thick n-InP buffer layer is grown on an n-InP substrate from a tin-indium melt at a cooling rate of 0.3-0.5°C/min.