WO2016013954A1

WO2016013954A1 - Cascade photoconverter with quantum-sized structures

Info

Publication number: WO2016013954A1
Application number: PCT/RU2014/000564
Authority: WO
Inventors: Алексей Михайлович НАДТОЧИЙ; Михаил Викторович МАКСИМОВ; Алексей Евгеньевич ЖУКОВ; Николай Александрович КАЛЮЖНЫЙ; Сергей Александрович МИНТАИРОВ
Original assignee: Общество с ограниченной ответственностью "Солар Дотс"
Priority date: 2014-07-25
Filing date: 2014-07-25
Publication date: 2016-01-28
Also published as: RU2017102273A; RU2017102273A3

Abstract

The invention relates to semiconductor photo-converters (solar cells) which convert the energy of photons of light into electricity, and can be used in the semiconductor industry for creating systems for generating electrical energy. The essence of the proposed invention consists in increasing the photocurrent of two sub-cells by means of using active semiconductor layers consisting of regions having various thicknesses and concentrations of indium atoms. The technical result of the present solution consists in creating a cascade photoconverter which allows for simultaneously expanding the spectral range of photosensitivity and for improving the efficiency thereof.

Description

CASCADE PHOTO CONVERTER WITH QUANTUM SIZE

STRUCTURES

The invention relates to semiconductor photoconverters (solar cells), which convert the energy of light photons into electricity, and can be used in the semiconductor industry to create systems for generating electrical energy.

State of the art

In recent decades, interest in renewable energy sources, in particular, in the possibility of using solar energy, has constantly increased in the world. For spacecraft, photovoltaics (solar energy) is the only source of energy, which largely determines its development, however, in recent years, the share of photovoltaics in the total energy generated by ground-based power plants.

The development of cascade photoconverters (FPs) that convert concentrated radiation is one of the most promising ways to achieve parity of solar energy with traditional sources. The efficiency of cascade FPs exceeds the efficiency of silicon by 2-3 times, and the cost can be significantly reduced when using cheap lenses that concentrate solar radiation on small-sized FP chips. At the same time, the need for expensive heterostructures of cascade phase transitions, and, consequently, the cost of energy, decreases in proportion to the concentration factor, which in modern solar photovoltaic plants reaches 500 - 1000 suns.

The main problem of the most promising cascade photoconverters suitable for industrial production today, based on the GalnP / GalnAs / Ge materials matched by the lattice parameter, is the inconsistency of the currents generated by photoactive pn junctions (subcells) of such a structure. This leads to the fact that their efficiency is about 39%, with a theoretical limit of more than 50%.

A significant limitation on the efficiency of cascade phase transitions is imposed by the properties of semiconductor materials from which their subelements are made. First of all, this refers to the crystal lattice parameter. The presence of a mismatch of materials with respect to the lattice parameter leads to the accumulation of elastic stresses, which will relax when a certain thickness is reached with the formation of defects. The need for harmonization of materials on the lattice parameter imposes restrictions on the absorption edge of bulk materials, since for semiconductor solid solutions a change in the absorption edge, which is possible only with a change in composition, usually leads to a change in the lattice parameter of the material. Thus, providing the possibility of expanding the spectral range of the photosensitivity of subcells of cascade phase transitions, which entails an increase in the photocurrent generated by them, is an important task for realizing the efficiency potential of cascade photoconverters.

One of the ways to change the absorption edge of semiconductor materials, which ensures the expansion of the photosensitivity of the subcells of phase transitions, is the use of quantum-sized structures, i.e. active semiconductor layers in which the sizes of individual regions are in the range of 5-50 nm. At such sizes, quantum effects can appear in the structures. Quantum-sized structures usually include quantum wells (QWs) or quantum dots (QDs), which allow one to change the absorption edge of a bulk material, but they also have a number of limitations. The use of QWs allows one to obtain a high level of quantum efficiency due to the fact that QWs absorb the entire surface; however, the long-wavelength shift of the absorption edge remains small. When using QDs, there is the possibility of a significant shift of the absorption edge, but it is impossible to obtain a high level of quantum efficiency due to the low surface density of such QDs.

A cascade photoconverter with quantum-well structures is known (see US patent 7,863,516, issued January 4, 2011), including a Ge or GaAs substrate, a set of photoactive transitions, one of which includes layers of self-organized InGaAs QDs separated by spacer layers from GaAs, AlGaAs or GaPAs, while effective the band gap of this transition is 1.16 eV.

A disadvantage of the known photoconverter with quantum-well structures is the low density of QDs, which is reflected in their low absorption of photons, as well as a low current of the upper transition from Gao ₅ Ιη ₀ .5Ρ.

Known cascade photoconverter with quantum-well structures (see patent CN 103280482, issued April 29, 2012), including a photoactive semiconductor Ge substrate, two photoactive pn junctions from Ino oiGaowAs and Gao sIno sP. Moreover, the average transition based on In _{0 0} iGao ₉ As includes several InAs layers of quantum dots and a layer modulating the elastic stresses of the lattice of In _x Gai _-x As.

A disadvantage of the known photoconverter with quantum-well structures is the low density of QDs, which is reflected in their low absorption of photons, as well as a low current of the upper junction from Gao. ₅ Ino. ₅ P.

The closest to the present technical solution in terms of the set of essential features is a cascade photoconverter with quantum-sized structures (see patent JP 2013115249, extruded 29.1 1.2011), adopted as a prototype and including a photoactive semiconductor substrate and several photoactive pn junctions, at least one of which includes several layers of CT.

An important role in the structure of the cascade photoconverter prototype is played by arrays of quantum dots, the use of which allows one to increase the photocurrent of the corresponding subcell.

The disadvantage of the known photoconverter prototype is the low absorption in arrays of standard quantum dots, which makes it impossible to ensure current matching for a cascade photoconverter based on GalnP / GalnAs / Ge.

Technical challenge

The objective of this solution is to create a cascade photoconverter with quantum-well structures, providing the possibility of simultaneously expanding the spectral range of the photosensitivity of two subcells based on GalnP and GalnAs, which entails the possibility of fully matching the currents of the cascade photoconverter based on GalnP / GalnAs / Ge and achieving an increased value of its efficiency. The increase in efficiency occurs due to an increase in the photocurrent of subcells during the propagation of spectral sensitivity to the long-wavelength region, as well as due to the provision of a high level of photogeneration and separation of charge carriers in quantum-sized structures.

Decision

To solve the technical problem, a cascade photoconverter with quantum-sized structures is proposed, including

but. a semiconductor substrate, in which the front surface is misoriented from the crystallographic plane (100),, b. at least one photoactive pn junction consisting of a semiconductor material including arsenic (As) and gallium (Ga) atoms, containing at least one active quantum-well semiconductor layer comprising gallium (Ga) indium (In) atoms and arsenic (As), consisting of regions with different thickness and concentration of indium atoms (In), p. and at least one photoactive pn junction consisting of a semiconductor material comprising phosphorus (P) and gallium (Ga) atoms, containing at least one active quantum-well semiconductor layer comprising indium (In) atoms, gallium (Ga ) and phosphorus (P), consisting of regions with different thickness and concentration of indium atoms (In).

As a possible implementation of the invention, a cascade photoconverter is proposed in which the active semiconductor layers contain enriched and depleted indium (In) regions.

As a possible implementation of the invention, a cascade photoconverter is proposed in which the substrate is made of Ge or GaAs.

As a possible implementation of the invention, a cascade photoconverter is proposed in which GaAs, GalnAs or AlGalnAs are used as the material of the photoactive pn junction, consisting of a semiconductor material including arsenic and gallium atoms.

As a possible implementation of the invention, a cascade photoconverters, in which the active semiconductor layer comprising indium gallium and arsenic atoms, vsholnen of In _x Gai _-x As with the average content x of indium (30-50) at. %

As a possible implementation of the invention, a cascade photoconverter is proposed, in which GalnP or AlGalnP is used as the material of the photoactive pn junction, consisting of a semiconductor material including phosphorus and gallium atoms.

As a possible implementation of the invention, a cascade photoconverter is proposed in which the active semiconductor layer, including indium gallium and phosphorus atoms, is made of In _x Ga _1-x P with an average content of x indium (10-20) at. % As a possible implementation of the invention, a cascade photoconverter is proposed, in which on the -GaAs substrate, in which the front surface is 6 degrees misoriented from the crystallographic plane (100), a buffer layer of -GaAs is sequentially deposited, the lower photoactive transition including a sequentially deposited back potential layer of barrier / -? AlGaAs or -GalnP, a base layer of / -? GaAs, a layer of undoped GaAs, comprising at least 10 active semiconductor layers based on in _x Gai _-x as with the average content x yn Ia (30-50) at. % separated by spacers made of GaAs, an emitter layer of l-GaAs and a layer of a wide-gap window of i-AlGaAs or a two-layer wide-gap window, comprising a layer of i-GaInP and a layer of l-APR, a tunnel diode containing sequentially deposited layers AJ ⁺⁺ -GaAs or p ⁺⁺ -GalnP and a ⁺⁺ -AlGaAs layer, the top photoactive transition including a successively deposited back-potential barrier layer from β-AlGaInP, a base layer from -GalnP, an undoped layer from GalnP, including at least at least 10 active semiconductor layers based on In _x Gai _-x P with medium soda neighing x indium (10-20) at. % separated by spacers made of GalnP, an emitter layer of p-GalnP and a wide-gap window layer of l-ANPR, as well as a contact sublayer of l-GaAs.

As a possible implementation of the invention, a cascade photoconverter is proposed in which a GalnP nucleation layer is sequentially deposited onto the -Ge substrate, whose front surface is 6 degrees misoriented from the crystallographic plane (100), creating a lower photoactive transition in the germanium substrate due to diffusion of phosphorus atoms , a buffer layer of l-GaInAs, with an indium content of 0-2%, the lower tunneling diode, which includes successively deposited layers of the wide-gap barrier, the l ⁺⁺ layer and p ⁺⁺ layer, the average photoactive transition an od, including a layer of the back potential barrier of β-AlGaAs or p-GalnP, a base layer of β-GalnAs with an indium content of 0-2%, an undoped layer of GalnAs with an indium content of 0-2%, including at least 10 active semiconductor layers based on In _x Gai _-x As with an average content of x indium (30-50) at. % separated by spacers made of GalnAs with an indium content of 0-2%, an emitter layer of p-GalnAs with an indium content of 0-2%, and a layer of a wide-gap window from i-AlGaAs or a two-layer wide-gap window, including a layer from p- GalnP and a layer of l-APR, the upper tunneling diode containing successively deposited layers of " ⁺⁺ -GaAs or" ⁺⁺ -GaInP and layer /? ⁺⁺ -AlGaAs, upper photoactive transition, including a sequentially deposited back-potential barrier layer from -AlGalnP, a base layer from -GalnP, an undoped layer from GalnP, comprising at least 10 active semiconductor layers based on In _x Gai _-x P with an average content x india (10-20) at. %, separated by spacers made of GalnP, an emitter layer of p-GalnP and a wide-gap window layer of i-APR, as well as a contact sublayer of p-GalnP with an indium content of 0-2%.

Blueprints

This technical solution is illustrated by drawings, where:

in FIG. 1 is a schematic cross-sectional view of a real cascade photoconverter with quantum-well structures; in FIG. Figure 2 shows the image of transmission electron microscopy (TEM) of the cross section of samples containing active semiconductor layers based on an In _x Ga _1-x As layer with an average indium composition of x = 30 at. %;

in FIG. 3 is a cross-sectional TEM image of the samples containing the active semiconductor layers based on the layer of In _x Gai _-x As with average indium composition of X = 40 at. %;

in FIG. Figure 4 shows a TEM of the cross section of samples containing active semiconductor layers based on an InxGa ^ As layer with an average indium composition of x = 50 at. %;

in FIG. 5 shows the spectral characteristics of the external quantum efficiency of a GaAs sub-cell of a cascade photoconverter without active layers of the present invention (curve 1) and a GaAs sub-cell of a cascade photoconverter of the present invention, including 10 active semiconductor layers based on an In _x Ga _1-x As layer with an average indium x composition = 30 at. % (curve 2);

in FIG. 6 shows the spectral characteristics of the external quantum efficiency of the GalnP subcell of the cascade photoconverter without active layers of the present invention (curve 3) and the GalnP subcell of the cascade photoconverter of the present invention, including 10 active semiconductor layers based on an In _x Ga _1-x P layer with an average indium composition of x = 10 at. % (curve 4).

Detailed Solution Description

New in the cascade photoconverter is the expansion of the spectral sensitivity of two photoactive transitions of the cascade phase transition at the same time due to the use of quantum-dimensional structures based on layers with a spatial change in thickness and composition obtained by growing on a semiconductor substrate in which the front surface is misoriented from the crystallographic plane (100).

The expansion of the spectral sensitivity of the GalnP subelement, along with the expansion of the spectral sensitivity of the GalnAs subelement, makes it possible to increase the photocurrent of the cascade phase transition and ensure full matching of the currents of the GalnP / GalnAs / Ge subcells.

Disorientation of the front surface of the semiconductor substrate relative to the crystallographic plane (100) ensures the formation of atomic steps on the front surface of which, during growth, high-density arrays of spatial regions with different indium contents are created in the region of the active semiconductor layer, providing a quantum effect of three-dimensional localization of charge carriers. Moreover, the relaxation of elastic stresses leads to the fact that regions with a high indium content have a greater thickness with respect to regions with a lower indium content.

Using the quantum-sized structures of the present invention, which are layers consisting of regions with different thicknesses and concentrations of indium atoms, it is possible to obtain a high absorption level due to the fact that such layers, unlike QDs, cover the entire surface of the phase transition, and due to the high structural quality due to relaxation of the elastic stresses of the lattice with a spatial change in thickness and composition.

The present cascade photoconverter with quantum-well structures is shown in FIG. 1. It consists of a semiconductor substrate 1, in which the front surface is misoriented from the crystallographic plane (100) of at least one photoactive pn junction 2, for example, from GalnAs with an indium content of 0-2%, containing at least one active semiconductor layer 3, for example, of In _x Ga _1-x As with an average content of x india (30-50) at. %, consisting of regions with different thicknesses and concentrations of indium atoms, and at least one photoactive pn junction 4, for example, from GalnP, containing at least one active semiconductor layer 5, for example, from In _x Gai. _x P with an average content of x indium (10-20) at. %, consisting of regions with different thickness and concentration of indium atoms.

The use of the proposed cascade photoconverter with quantum-well structures will increase the photocurrents of the subcells of cascade photovoltaic cells, which is primarily important for increasing the conversion efficiency of the most promising three-junction converter photodiodes today based on strictly isoperiodic semiconductor materials Gao.5 \ 1p ₀ . ₄ 9P / Gao.99lno.oi As / Ge.

As is known, Gao materials strictly matched by the lattice parameter are known. ₅ iIno ₄ 9P (Eg = 1.9 eV), Gao gglno.oi As (E _g = 1.4 eV) and Ge (E _g = 0.66 eV) do not allow the implementation of the three-junction design, which is optimal from the point of view of spectral densities of photons FP. But due to the high stability of the parameters, even with prolonged operation and reproducibility of industrial technology, this structure is currently the main industrial trend, and has an efficiency of about 39% in production.

The main disadvantage of the combination of materials is Gao. ₅₁ In _{0 4} 9P - Gao 99ln ₀ . ₀₁ As - Ge is the large band gap of the middle Gao.99ln _{0 01} As subcell. For the terrestrial solar spectrum, in the case of absorption by each sub-element of all photons with an energy of a greater band gap of their material and the separation of all photogenerated carriers, the photocurrents of the sub-elements will be:

- 17.5 mA / cm for Gao.5iIno ₄ 9 subcell (all photons from 0 to 650 nm);

- 15.6 mA / cm ² for the Gao ^ Ino.oiAs subcell (all photons from 650 to 900 nm);

-

- 29.2 mA / cm for the Ge subcell (all photons from 900 to 1900 nm).

This leads to the fact that the minimum current (in the case of absorption of all photons with energies in the range of 1.9-1.4 eV) will generate an average subelement, and the current generated by the lower one will significantly exceed the currents of the upper and middle subelements. In this case, the total current of the cascade phase transition will be equal to the minimum of the currents of the subcells. Thus, the Ga ₀ 5 ₁ In ₀ 4 P / Ga ₀ 99ln ₀ oiAs / Ge structure operates in the mode of limiting the current to the average subcell. The essence of the invention is to increase the photocurrent of two subcells through the use of active semiconductor layers consisting of regions with different thickness and concentration of indium atoms. From the above values of the photocurrents of the subcells, it can be seen that if the photocurrent Gao ₉ 9ln ₀ oiAs of the subcell is increased by an amount of the order of 2 mA / cm ^{2, the} cascade phase transition including Gao s no ^ P and Gao.99ln ₀ oi As subcells will go into the current limit mode subelement. A further increase in the photocurrent, and hence the efficiency of the AF, will be possible only with an increase in the photocurrent of the upper subcell based on Gao.silno. ^ P. Thus, in order to obtain increased efficiency of cascade phase transitions, it is necessary to increase the photocurrents of two subcells at the same time, which is achieved in the present invention.

Using the original method of forming quantum-well structures based on active semiconductor layers from In _x Gai. _x As (3) and In _x Gai. _x P (5), consisting of regions with different thicknesses and concentrations of indium atoms created under certain growth conditions on a semiconductor substrate misoriented from the crystallographic plane (100), it is possible to obtain a much larger increase in the photocurrent of subcells in comparison with the known solutions based on QD and QW .

The active semiconductor layers of a real cascade photoconverter are illustrated by studies using transmission electron microscopy (TEM). Cross-sectional TEM images of structures with active semiconductor layers based on InxGa ^ As of an average composition of 30% (Fig. 2), 40% (Fig. 3) and 50% (Fig. 4) make it possible to see that the layers have interface irregularities (spatial variation) thickness) and various composition (spatial change in composition).

Using 10 active semiconductor layers based on In _x Gai- _x As with an average indium composition of x = 30 at. % (Fig. 5, curve 2) made it possible to expand the range of photosensitivity of the GaAs subcell up to 1,100 nm and obtain a photocurrent gain of 3.2 mA / cm.

Use of 10 active semiconductor layers based on In _x Gai. _x P with an average indium composition x = 10 at. % (Fig. 6 curve 4) made it possible to expand the range of photosensitivity of the GaAs subcell up to 800 nm and obtain a photocurrent gain of 1.4 mA / cm ² .

Claims

CLAIM

1. Cascade photoconverter with quantum-well structures, including

a. a semiconductor substrate, in which the front surface is misoriented from the crystallographic plane (100), b. at least one photoactive pn junction consisting of a semiconductor material including arsenic (As) and gallium (Ga) atoms, containing at least one active quantum-well semiconductor layer comprising gallium (Ga) indium (In) atoms and arsenic (As), consisting of regions with different thickness and concentration of indium atoms (In), c. and at least one photoactive pn junction consisting of a semiconductor material comprising phosphorus (P) and gallium (Ga) atoms, containing at least one active quantum-well semiconductor layer comprising indium (In) atoms, gallium (Ga ) and phosphorus (P), consisting of regions with different thickness and concentration of indium atoms (In).

2. The cascade photoconverter according to claim 1, characterized in that the active semiconductor layers contain enriched and depleted indium (In) region.

3. The cascade photoconverter according to claim 1, characterized in that the substrate is made of Ge or GaAs.

4. The cascade photoconverter according to claim 1, characterized in that GaAs, GalnAs or AlGalnAs are used as the material of the photoactive pn junction, consisting of a semiconductor material including arsenic and gallium atoms.

5. The cascade photoconverter according to claim 4, characterized in that the active semiconductor layer including indium gallium and arsenic atoms is made of In _x Gai. _x As with an average content of x indium (30-50) at. %

6. The cascade photoconverter according to claim 1, characterized in that GalnP or AlGalnP is used as the material of the photoactive pn junction, consisting of a semiconductor material including phosphorus and gallium atoms.

7. The cascade photoconverter according to claim 6, characterized in that the active semiconductor layer including indium gallium and phosphorus atoms is made of In _x Ga _1-x P with an average content of x indium (10-20) at. %

8. The cascade photoconverter according to claim 1, characterized in that on the -GaAs substrate, in which the front surface is 6 degrees misoriented from the crystallographic plane (100), a buffer layer of β-GaAs is deposited sequentially, the lower photoactive transition including sequentially deposited -AlGaAs or p-GalnP back potential barrier layer, -GaAs base layer, undoped GaAs layer, which includes at least 10 active _{x x} _1-x As based semiconductor layers with an average x indium content (30- 50) at. % separated by spacers made of GaAs, an emitter layer of l-GaAs and a layer of a wide-gap window of l-AlGaAs or a two-layer wide-gap window comprising a layer of i-GaInP and a layer of i-AIPR, a tunnel diode containing successively deposited layers p ⁺⁺ - GaAs or AJ ⁺⁺ -GaInP and ju ⁺⁺ -AlGaAs layer, upper photoactive transition including a sequentially deposited back-potential barrier layer from -AlGalnP, a base layer from p-GalnP, an undoped layer from GalnP, including at least at least 10 active semiconductor layers based on In _x Ga _1-x P with an average content of holding x indium (10-20) at. % separated by spacers made of GalnP, an emitter layer of p-GalnP and a wide-gap window layer of l-ANPR, as well as a contact sublayer of n-GaAs.

9. The cascade photoconverter according to claim 1, characterized in that on the p-Ge substrate, in which the front surface is 6 degrees misoriented from the crystallographic plane (100), a GalnP nucleation layer is successively deposited, which creates a lower photoactive transition in the germanium substrate due to diffusion of phosphorus atoms from the buffer layer H-GalnAs, with the indium content of 0-2%, the lower tunnel diode comprising sequentially osazhennye shirokozonnogo barrier layers, n ⁺⁺ -layer and the p ⁺⁺ -layer, average photoactive transition layer comprising a rear potential Nogo barrier of -AlGaAs or p-GalnP, a base layer of j ^ -GalnAs with indium content 0- 2%, an undoped layer of GalnAs from the indium content of 0-2%, comprising at least 10 active semiconductor layers based on In _x Gai . _x As with an average content of x indium (30-50) at. % separated by spacers made of GalnAs with an indium content of 0-2%, an emitter layer of p-GalnAs with an indium content of 0-2%, and a layer of a wide-gap window from l-AlGaAs or a two-layer wide-gap window, including a layer from l-AlGaAs GaInP and a layer of l-AIPR, upper tunnel diode containing successively deposited layers of ^{++ ++} GaAs or n ⁺⁺ -GaInP and layer /? ⁺⁺ -AlGaAs, upper photoactive transition, including a successively deposited back-potential barrier layer of p-AIGalnP, a base layer of p-GalnP, an undoped layer of GalnP, comprising at least 10 In _x Gai-based active semiconductor layers. _x P with an average content of x indium (10-20) at. % separated by spacers made of GalnP, an emitter layer of p-GalnP and a wide-gap window layer of i-ANPR, as well as a contact sublayer of p-GalnP with an indium content of 0-2%.