Low bandgap, monolithic, multi-bandgap, optoelectronic devices

Abstract

Low-bandgap, monolithic, multi-bandgap, optoelectronic devices (10), including PV converters, photodetectors, and LED's, have lattice-matched (LM), double-heterostructure (DH), low-bandgap GaInAs(P) subcells (22, 24) including those that are lattice-mismatched (LMM) to InP, grown on an InP substrate (26) by use of at least one graded lattice constant transition layer (20) of InAsP positioned somewhere between the InP substrate (26) and the LMM subcell(s) (22, 24). These devices are monofacial (10) or bifacial (80) and include monolithic, integrated, modules (MIMs) (190) with a plurality of voltage-matched subcell circuits (262, 264, 266, 270, 272) as well as other variations and embodiments.

Description

CONTRACTUAL ORIGIN OF INVENTION [0001] The United States Government has rights in this invention under Contract No. DE-AC36-99GO10337 between the United States D Renewable Energy Laboratory, a Division of the Midwest Research Institute.TECHNICAL FIELD [0002] This invention relates to optoelectronic devices, and, more specifically, to low bandgap, monolithic, multi-bandgap solar photovoltaic (SPV) and thermophotovoltaic (TPV) cells for converting solar and / or thermal energy to electricity as well as for related photodetector devices for detecting light signals and light emitting diode (LED) devices for converting electricity to light and / or infrared (IR) radiant energy. BACKGROUND OF THE INVENTION [0003] It is well known that the most efficient conversion of radiant energy to electrical energy with the least thermalization loss in semiconductor materials is accomplished by matching the photon energy of the incident radiation to the amount of energy needed to excite electrons in the s...

AI Technical Summary

Benefits of technology

[0024] The first subcell is preferably a lattice-matched, double-heterostructure, comprising homojunction layers of GaInAs(P) clad by InAsyP1-y cladding layers wherein the InAsyP1-y cladding has a value for y in a range of o≦y<1, such the InAsyP1-y cladding layers of the first subcell have a lattice constant equal to the first lattice constant. The second subcell is is also preferably a lattice-matched, double-heterostructure comprising homojunction layers of GaInAs(P) clad by InAsyP1-y cladding layers, wherein the InAsyP1-y cladding has a value for y in a range of o≦y<1, such that the InAsyP1-y cladding layer of the second subcell have a lattice constant equal to the second lattice constant. Either a tunnel junction or an isolation layer is also positioned between subcells. The InP substrate can be doped with deep acceptor atoms to make the substrate more electrically insulating, and, in bifacial structures, this feature allows the substrate to serve as an electrical isolation between subcells positioned on opposite sides of the substrate.

Problems solved by technology

However, since solar radiation and blackbody radiation usually comprise a wide range of wavelengths, use of only one semiconductor material with one bandgap to absorb such radiant energy and convert it to electrical energy will result in large inefficiencies and energy losses to unwanted heat.

Semiconductor compounds and alloys with bandgaps in the various desired energy ranges are known, but that knowledge alone does not solve the problem of making an efficient and useful energy conversion device.

Defects in crystalline semiconductor materials, such as impurities, dislocations, and fractures provide unwanted recombination sites for photogenerated electron-hole pairs, resulting in decreased energy conversion efficiency.

Lattice-mismatching (LMM) in adjacent crystal materials causes lattice strain, which, when high enough, is usually manifested in dislocations, fractures, wafer bowing, and other problems that degrade or destroy electrical characteristics and capabilities of the device.

Unfortunately, the semiconductor materials that have the desired bandgaps for absorption and conversion of radiant energy in some energy or wavelength bands do not always lattice match other semiconductor materials with other desired bandgaps for absorption and conversion of radiant energy in other energy or wavelength bands.

Therefore, fabrication of device quality, multi-bandgap, monolithic, converter structures is difficult, if not impossible, for some portions of the radiation frequency or wavelength spectrum.

This problem has been particularly difficult to solve in the infrared (IR) portion of the spectrum, where options for suitable, commercially available substrates on which to grow thin films with the necessary bandgaps for absorption and conversion of the infrared radiation to electrical energy are very limited, and where compatible, i.e., lattice-matched, semiconductor materials with the different bandgaps needed to absorb and convert different portions of the infrared spectrum efficiently are also quite limited.

While the current unavailability of efficient and cost-effective solar photovoltaic (SPV) converters, especially multi-bandgap, monolithic, converter devices, capable of absorbing and converting infrared (IR) radiation in wavelengths greater than 1.67 μm leaves substantial amounts of energy in the solar spectrum to remain unconverted to electricity, in state-of-the-art SPV's, it is an even greater problem for thermophotovoltaic (TPV) devices.

However, those Forrest et al., patent teachings, which were directed to pixel detection of near infrared radiation incident on a focal plane for telecommunications applications, are not useful in SPV and TPV applications.

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