RU2410794C2 - Semiconductor photoconverter and method of making said photoconverter - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: invention relates to design and technology of making optoelectronic devices and specifically to photoelectric converters. The semiconductor photoconverter has a working surface on which radiation is incident, a base area made in form of a plate of p- or n-type semiconductor material and doped layers with high n+- and p+-conductivity, lying on two sides of the plate, contacts to said doped layers and antireflection coating on the working surface. On the surface of the base area free from n+- and p+ doped layers, there are micro-depressions, one, two or three linear dimensions of which are comparable to a quarter of the radiation wavelength, corresponding to maximum spectral density of the radiation. Parts of the base area between the micro-depressions have doped layers whose surface is covered with metal contacts. The width of the doped layers and contacts between the micro-depressions is equal to 5-10 nm. The micro-depressions have antireflecting coating with passivating properties with the following parameters: radiation absorption coefficient 0.94-0.99, rate of effective surface recombination of 1-20 cm/s. Disclosed also is a method of making said photoconverter. ^ EFFECT: invention provides high efficiency of converting intense radiation streams. ^ 6 cl, 4 dwg,1 ex

Description

The invention relates to the field of design and manufacturing technology of optoelectronic devices, namely photoelectric converters (FP).

A known design and method of manufacturing silicon phase transitions in the form of a diode structure with a pn junction on the front side, current collector metal contacts to the doped layer in the form of a comb, a solid back contact and an antireflection coating on the front (working) side (Vasiliev AM, Landsman A.P. Semiconductor photoconverters, M .: Soviet Radio, 1971). The FP manufacturing process is based on diffusion doping of the front side with phosphorus, chemical deposition of the nickel contact, selective etching of the contact pattern and the application of an antireflection coating. The disadvantage of the obtained phase transitions is the relatively large depth of the pn junction and, as a consequence, the low value of their efficiency.

A known design and method of manufacturing silicon phase transitions with a shallow pn junction on most of the front side and a deep pn junction under metal contacts (Green MA, Blakers AW et al. Improvements in flat-plate and concentrator silicon solar cell efficiency // 19th IEEE Photovolt. Spec. Conf., New Orleans, 1987 .-- P.49-52). The manufacturing process includes the following operations on the front side: diffusion alloying to a depth of less than 0.5 microns, thermal oxidation, laser scribing of grooves, chemical etching of silicon in the grooves, diffusion alloying of the surface of the grooves to a depth of more than 1 micron, and electrochemical deposition of nickel and copper into the grooves . The disadvantage of the resulting AF is an increase in the thickness of the initially created alloy layer during diffusion doping of the grooves and, as a consequence, the low efficiency of the AF.

A known design and method for manufacturing a phase transition with an oxide film on the front side, free from doped layers and contacts, which are created on the back in the form of alternating point strongly doped regions, forming pn junctions and isotype transitions (Sinton RA, Swanson RM An optimization study of Si point-contact concentrator solar cell // 19 ^th IEEE Photovolt. Spec. Conf., New Orleans, 1987. NY, 1987. - P.1201-1208). The disadvantage of these phase transitions is the need for repeated photolithographic etching operations, which complicates the manufacturing process and increases the cost of phase transitions.

A known FP design with a two-sided working surface with an n ⁺ -p-p ⁺ diode structure, in which the configuration and contact area on the back side coincide in plan with the configuration and contact area on the working side, and the thickness of the base region does not exceed the diffusion length of minority charge carriers (US patent No. 3948682, CL 136/84, from 04/06/1976). The design drawback is the presence on the entire working and back surfaces of a heavily doped layer, the upper layers of which have a very low diffusion length of minority charge carriers, which reduces the efficiency of such phase transitions.

As a prototype, the design of a photoconverter with a double-sided working surface, containing diode structures with n ⁺ -p (p ⁺ -n) junctions on the front surface of the silicon wafer and isotype pp ⁺ (nn ⁺ ) junctions in the base region on the back surface of the silicon wafer, where the areas and configurations of metal contacts on the front and back surfaces coincide in plan, and the thickness of the photoconverter is commensurate with the diffusion length of minority current carriers in the base region, the diode structures are made in the form of separate sections connected by contacts, combined in plan on the front and back surfaces with areas on which the contacts are applied, the distance between separate adjacent sections with p ⁺ -n (n ⁺ -p) junctions, as well as between separate adjacent sections with p ⁺ -p (n ⁺ -n) isotype transitions does not exceed the diffusion length of minority current carriers in the base region, on surfaces free of n ⁺ -p (p ⁺ -n) junctions and p ⁺ -p (n ⁺ -n) isotype junctions made passivating dielectric film.

In the prototype of a method of manufacturing photovoltaic converters with a double-sided working surface from silicon wafers, including chemical etching of the surface, creation of a passivating antireflection film and windows on the front side of the film, doping of silicon in the windows, respectively, with a donor and acceptor impurity to a depth of more than 0.5 μm to form pn junctions using heat treatment and applying a metal contact into the windows, windows 1-50 microns wide are created in a passivating antireflection film of Si _x N _y , place the windows from each other at a distance not exceeding twice the diffusion length, and from the end of the photoconverter at a distance not exceeding the diffusion length of minority charge carriers in the base region, and cover the entire surface of the windows with a metal contact, create a passivating antireflection film Si _x on the back N _y , in the film open windows with a width of 1-50 μm, combining in plan with windows on the front surface, place windows from each other at a distance not exceeding doubled diffusion length, and from the end educators at a distance not exceeding the diffusion length of minority charge carriers in the base region, the windows are doped using heat treatment to form isotype transitions, the entire silicon surface in the windows is covered with a metal contact (RF patent No. 2331139 dated 02.28.2007).

A disadvantage of the known AF design is a large series resistance in the base region and a decrease in efficiency in the conversion of concentrated radiation.

The task of the invention is to increase the conversion efficiency of intense radiation fluxes.

The technical result is achieved by the fact that in a semiconductor photoconverter containing a working surface on which radiation is incident, a base region made in the form of a plate of semiconductor material of p- or n-type conductivity and doped layers with high conductivity of n ⁺ and p ⁺ type, located on both sides of the plate, contacts to said doped layers and antireflection coating on the working surface, on the surface of the base region free of layers doped n ⁺ - and p ⁺ -type are formed micropitting, odi m, two or three linear sizes of which are commensurate with one fourth wavelength corresponding to the maximum spectral density of radiation, sections of the base region between microdeeps contain doped layers, the surface of which is covered with metal contacts, the width of the doped layers and contacts between microdeeps is 5-10 nm, microdepths contain an antireflection coating with passivating properties with the following parameters: radiation absorption coefficient 0.94-0.99, effective surface speed recombination 1-20 cm / sec.

In the embodiment of the semiconductor photoconverter, the silicon base region contains microspheres in the form of halves of microspheres with a radius of 0.2--0.3 μm on the working and back surfaces, and the antireflection coating is made of silicon nitride mixed with hydrogen.

In another embodiment, the designs of the semiconductor photoconverter microdeep on the working and back surfaces are made in the form of squares arranged in the form of cells in the centers of a rectangular contact grid.

In another embodiment, the design of the semiconductor micro-cavity photoconverter in the form of half cylinders and contact layers are made in the form of alternating extended structures, the length of which is 10-10 ⁶ times their width.

In the method of manufacturing a semiconductor photoconverter by creating on the opposite surfaces of the base region, made in the form of a semiconductor wafer, doped layers of n ⁺ and p ⁺ type, deposition of metal contact layers and antireflection coating, after creating doped layers of n ⁺ and p ⁺ type and deposition of metal contact layers, selectively open windows in the doped and contact layers corresponding to the shape of microdepths, and form microdepths in the base region using the plasma method chemical or chemical etching, the width of the doped layers and contacts between microdeeps will be 5-10 nm, and one, two or three linear sizes of the formed microdeeps are commensurate with one fourth wavelength corresponding to the maximum spectral radiation density, then they create an antireflective and passivating coating.

To reduce the complexity of manufacturing a semiconductor photoconverter, windows are opened by laser or diamond engraving.

The invention is illustrated in figures 1-4, where figure 1 shows the design of the photoconverter with microdepth in the base region in the form of microspheres, figure 2 - microdepth in the form of a honeycomb structure, figure 3 - microdepth in the form of squares installed in in the form of cells in the centers of a rectangular contact grid, Fig. 4 is a plan view and a cross-section of a photoconverter in the form of alternating extended microdeeps and pn junctions with contact strips whose length is 10-10 ⁶ more than their width.

In Fig. 1, the photoconverter consists of a crystalline silicon wafer with a base region of 1, sections of diode structures with n ⁺ -p (p ⁺ -n) junctions 2 on the working surface 3, and an isotypic р-р ⁺ (nn ⁺ ) junction 4 on the back surface 5, metal contacts 6 over the entire area of p ⁺ -n (n ⁺ -p) junctions 2 and metal contacts 7 over the entire area of isotypic p ⁺ -p (n ⁺ -n) junctions 4. p ⁺ -n (n ⁺ -p ) transitions 2 and contacts 6 and 7 are located on the working 3 and back 5 surfaces around the perimeter 8 of microdepths 9, made in the form of halves of microspheres with a radius r = 0.1-0.2 μm, Some of them contain an antireflection coating 10 made of silicon nitride with passivation of the silicon surface with hydrogen with the following parameters: radiation absorption coefficient 0.92-0.99, effective recombination rate on the surface of microdeeps 9 9-20 cm / s. The thickness of the doped layers 11 in the regions with p ⁺ -n (n ⁺ -p) transitions 2 and the doped layers 12 in the regions of the isotype p-p ⁺ (nn ⁺ ) transition 4 is 0.2-1 μm, the width d of the doped layers 11 and 12 and metal contacts 6 and 7 is 5-10 nm.

In figure 2, microdepths 9 are made in the form of a honeycomb structure. Along the perimeter 8 of the micro-depressions P, pn junctions 2 and metal contacts 6 are made.

In figure 3, the microcavities 9 on the working surface 3 are made in the form of squares installed in the form of cells with borders in the form of a rectangular contact grid 13.

In Fig. 4, microdeeps 9 are made in the form of extended strips 14, the length l of which is 10-10 ⁶ times their width D = 2r. The contact layers 15 and sections with p ⁺ -n (n ⁺ -p) junctions 16 are located around the perimeter of the strips 14, and their width d is 10-20 times less than the width of the microdeeps 9. The microdeepings of the extended strips 14 are made in the form of half-cylinders with a diameter of D = 2r on the working 3 and on the back 5 surfaces of the photoconverter. The contact layers 15 are combined using transverse contact strips 77 on the working 3 and rear 5 surfaces to divert electricity from the photoconverter to an external network.

Photoconverter works as follows. The radiation falls into microdeeps 9, which play the role of volume resonators, in which a standing electromagnetic wave is formed. Under the action of radiation in the base region 7, nonequilibrium charge carriers are generated: electrons and holes. Minor charge carriers are repelled from the back by the electric field of the isotype p-p ⁺ (nn ⁺ ) junction 4, are collected by the electric field p ⁺ -n (n ⁺ -p) junction 2 and through the contacts 7 they go to a load (not shown). The antireflection coating 10 on the surface of the microdepth 9 increases the absorption of radiation to 92-99% and, due to the passivation of the surface of the microdepth 9, reduces the surface recombination rate to a value of 1-20 cm / s, as a result, the collection efficiency of minority carriers increases and the photocurrent increases.

Photoconverter manufacturing example

Single-crystal or coarse-grained polycrystalline silicon wafers with a thickness of 180 μm p-type with a lifetime of 20 μs are used. By diffusion on the back side of the 5 plates, an isotypic pp ⁺ transition 4 is created, and on the front surface 3 the n ⁺ -p transition 2 with a thickness of the doped layers 11 is about 1 μm. On both surfaces 3 and 5 of the photoconverter, a continuous metal contact 6 and 7 of the layers of nickel, copper and chromium is applied. Using photolithography, the metal films 6 and 7 and the doped layers 11 are etched, creating windows corresponding to the shape of the microcavities, and microcavities 9 are created in the base region 7 in accordance with FIGS. 1-4 by selective plasma-chemical or chemical etching. Then passivation of the surface of the micro-depressions 9 with hydrogen is carried out and an antireflection film 10 of silicon nitride is applied by plasma-chemical deposition of a mixture of monosilane and ammonia.

Reducing the cost of opening windows is achieved by using instead of photolithography the method of engraving the surface of the plate with a laser or diamond tool.

The considered constructions and manufacturing technologies make it possible to create photoconverters based on silicon, germanium, silicon carbide, and other materials, as well as form n ⁺ and p ⁺ layers from semiconductors with a larger band gap than in the base region, creating silicon - amorphous silicon heterojunctions.

For silicon, the radius of microdeeps 9 is 0.2-0.3 microns, for germanium r = 0.3-0.45 microns, for silicon carbide r = 0.1-0.15 microns. The small sizes of microdeeps P, one, two or three linear sizes of which are comparable with one fourth of the radiation wavelength, allow the use of microdeeps as resonators of electromagnetic waves and reduce ohmic losses in the base region and increase the efficiency of the photoconverter when converting concentrated radiation fluxes.

Claims (6)

1. A semiconductor photoconverter containing a working surface on which radiation is incident, a base region made in the form of a plate of semiconductor material of p- or n-type conductivity, and doped layers with high conductivity of n ⁺ and p ⁺ type, located on both sides plate contact to said doped layers and antireflection coating on the working surface, characterized in that on the surface of the base region free of layers doped n ⁺ - and p ⁺ -type are formed micropitting, one, two or three linear the sizes of which are commensurate with one fourth wavelength corresponding to the maximum spectral radiation density, sections of the base region between microdeeps contain doped layers, the surface of which is covered with metal contacts, the width of the doped layers and contacts between microdeeps is 5-10 nm, microdepths contain an antireflection coating with passivating properties with the following parameters: radiation absorption coefficient 0.94-0.99, effective surface recombination rate 1-20 cm / s. 2. The semiconductor photoconverter according to claim 1, characterized in that the silicon base region contains microspheres in the form of halves of microspheres with a radius of 0.2-0.3 μm on the working and back surfaces, the antireflection coating is made of silicon nitride with hydrogen passivation. 3. The semiconductor photoconverter according to claim 1, characterized in that the microdeeps on the working and back surfaces are made in the form of squares installed in the form of cells in the centers of a rectangular contact grid. 4. The semiconductor photoconverter according to claim 1, characterized in that the microcavities in the form of half cylinders and contact layers are made in the form of alternating extended structures, the length of which is 10-10 ⁶ times their width. 5. A method of manufacturing a semiconductor photoconverter by creating on the opposite surfaces of the base region, made in the form of a semiconductor wafer, doped n ⁺ - and p ⁺ -type layers, applying metal contact layers and an antireflective coating, characterized in that after creating the doped n ⁺ - layers and p ⁺ -type and deposition of metal contact layers selectively open windows in the alloyed and contact layers, corresponding to the shape of microdepths, and form microdepths in the base areas by plasma-chemical or chemical etching, the width of the doped layers and contacts between microdeeps is 5-10 nm, and one, two or three linear sizes of the formed microdeeps are comparable with one fourth wavelength corresponding to the maximum spectral radiation density, then create on the surface of the microdepths antireflective and passivating coatings. 6. A method of manufacturing a semiconductor photoconverter according to claim 5, characterized in that the opening of the windows is carried out by laser or diamond engraving.

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