The author begins with an Introduction in which he discusses basic concepts, recent developments, potential advantages offered by TPV systems and a historical background. He then provides a background in blackbody radiators and examines selective and rare-earth oxide radiators. He discusses modelling, fabrication and characterization of TPV convertors, particularly those based on GaSb and InGaAs. He examines the several approaches to recirculating the sub-bandgap photons and ends with a section on modelling of TPV system performance, and conceptual designs and demonstration of TPV systems, including solar powered, biofueled nuclear-fueled, liquid hydrocarbon-fueled, diesel-fueled, propane fueled, and natural gas fueled TPV systems.

A review of progress in thermophotovoltaic generation of electricity

A high temperature thermophotovoltaic (TPV) system is modeled and its system level performance is assessed in the context of concentrated solar power (CSP) with thermal energy storage (TES). The model includes the treatment of the emitter and the heat transfer fluid that draws thermal energy from the TES, which then allows for the identification and prioritization of the most important TPV cell/module level properties that should be optimized to achieve maximum performance. The upper limiting efficiency for an idealized system is then calculated, which shows that TPV with TES may one day have the potential to become competitive with combined cycle turbines, but could also offer other advantages that would give CSP an advantage over fossil based alternatives. The system concept is enabled by the usage of liquid metal as a high temperature heat transfer and TES fluid. The system concept combines the great economic advantages of TES with the potential for low cost and high performance derived from TPV cells fabricated on reusable substrates, with a high reflectivity back reflector for photon recycling.

Thermophotovoltaics: a potential pathway to high efficiency concentrated solar power

We present a growth technique which combines wet-chemical growth and molecular beam epitaxy (MBE) to create complex semiconductor nanostructures with nanocrystals as active optical material. The obtained results show that wet-chemically prepared semiconductor nanocrystals can be incorporated in an epitaxally grown crystalline cap layer. As an exemplary system we chose CdSe nanorods and CdSe(ZnS) core-shell nanocrystals in ZnSe and discuss the two limits of thin (d approximately 2R) and thick (d>2R) ZnSe cap layers of thickness d for CdSe nanorods and nanodots of radii R between 2 and 4 nm. In contrast to the strain-induced CdSe/ZnSe Stranski-Krastanow growth of a quantum dot layer in a semiconductor heterostructure, the technique proposed here does not rely on strain and thus results in additional degrees of freedom for choosing composition, concentration, shape, and size of the nanocrystals. Transmission electron microscopy and X-ray diffractometry show that the ZnSe cap layer is of high crystalline quality and provides all parameters for a consecutive growth of Bragg structures, waveguides, or diode structures for electrical injection.

Hybrid Epitaxial−Colloidal Semiconductor Nanostructures

A method for growing a silicon carbide single crystal on a single crystal substrate comprising the steps of heating silicon in a graphite crucible to form a melt, bringing a silicon carbide single crystal substrate into contact with the melt, and depositing and growing a silicon carbide single crystal from the melt, wherein the melt comprises 30 to 70 percent by atom, based on the total atoms of the melt, of chromium and 1 to 25 percent by atom, based on the total atoms of the melt, of X, where X is at least one selected from the group consisting of nickel and cobalt, and carbon. It is possible to improve morphology of a surface of the crystal growth layer obtained by a solution method.

Method for growing silicon carbide single crystal

Selective epitaxy and lateral overgrowth of 3C-SiC on Si – A review

Experimental assessment of metal solvents for low-temperature liquid-phase epitaxy of silicon carbide

Vapor-phase epitaxial lateral overgrowth of ZnSe on GaAs

We survey and assess new concepts for “next-generation” GaSb-based thermophotovoltaic (TPV) devices. The objectives are new device structures with novel back mirror designs to better utilize photon recycling effects, isolation schemes to realize monolithic, series-interconnected TPV arrays, and reduced cost by the use of surrogate substrates in place of GaSb or InAs wafers. The processes considered include 1. liquid-phase epitaxial lateral overgrowth on patterned, masked substrates, 2. epitaxial film transfer or wafer fusion techniques, 3. epitaxial growth of GaSb alloys on high resistivity (lattice matched) ZnTe, 4. realization of semi-insulating III-V antimonides, 5. selective wet oxidation of Al-containing antimonides (e.g., AlAsSb) wherein a the semiconducting epitaxial layer is converted to Al2O3 to form a buried insulating layer, and 6. GaSb- and InAs-on-silicon heteroepitaxy.

New concepts for III-V antimonide thermophotovoltaics

Optical cavity light-emitting diode structures with 'buried' mirrors, and their fabrication by lateral epitaxy are described. Single-crystal, high-quality epitaxial layers are formed over substrates coated with patterned, reflective masks using liquid-phase or vapor-phase epitaxial lateral overgrowth processes. The reflecting mask acts as a backside mirror and forms an optical cavity leading to enhanced external quantum efficiencies. An AlGaAs optical cavity LED incorporating a refractory metal 'buried' mirror is assessed: a greater than 3-fold increase in output optical power is measured compared to control devices with no buried mirror. Application of the epitaxial overgrowth techniques to LED structures utilizing electron-beam deposited dielectric/semiconductor 'buried' mirrors and to other semiconductor materials, such as InGaAsSb, SiC, and ZnSe is described.

Resonant cavity LEDs by lateral epitaxy

InGaP/GaAs photovoltaic-photoelectrochemical (PV-PEC) cells made by MOCVD on GaAs substrates have demonstrated high conversion efficiencies for the direct generation of hydrogen from sunlight and water [KHASALEV and TURNER, Science, 17 April 19981. The present work is an experimental effort to develop and assess potential low-cost alternative fabrication technologies for such PV-PEC cells. Our strategy is to utilize a cheap silicon substrate and simple epitaxial growth techniques. Since PV-PEC cells do not require a semiconductor p-n junction nor front metallization, a mesaarray device structure is proposed that can be made by selective epitaxy. Selective epitaxy of small-area (IO to 100 microns on a side) mesas should yield significant stress and defect reduction. We describe the fabrication of such cells with GaAs-on-silicon heteroepitaxy by a closespaced vapor transport (CSVT) technique in combination with selective InGaP liquid-phase epitaxy (LPE).

http://ieeexplore.ieee.org/iel5/7320/19792/00916128.pdf

Michael G. Mauk

Papers

Experimental assessment of metal solvents for low-temperature liquid-phase epitaxy of silicon carbide

Vapor-phase epitaxial lateral overgrowth of ZnSe on GaAs

New concepts for III-V antimonide thermophotovoltaics

Resonant cavity LEDs by lateral epitaxy

SELECTIVE HETEROEPITAXY OF InGaP/GaAs/SILICON DEVICES FOR GENERATING HYDROGEN FROM SUNLIGHT