The authors demonstrate a thin, Ge-free III–V semiconductor triple-junction solar cell device structure that achieved 33.8%, 30.6%, and 38.9% efficiencies under the standard 1sun global spectrum, space spectrum, and concentrated direct spectrum at 81suns, respectively. The device consists of 1.8eV Ga0.5In0.5P, 1.4eV GaAs, and 1.0eV In0.3Ga0.7As p-n junctions grown monolithically in an inverted configuration on GaAs substrates by organometallic vapor phase epitaxy. The lattice-mismatched In0.3Ga0.7As junction was grown last on a graded GaxIn1−xP buffer. The substrate was removed after the structure was mounted to a structural “handle.” The current-matched, series-connected junctions produced a total open-circuit voltage over 2.95V at 1sun.

The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system-PV modules for portable applications that operate at greater than 50% efficiency. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space. Our approach is driven by proven quantitative models for the solar cell design, the optical design, and the integration of these designs. Optical systems efficiency with an optical efficiency of 93% and solar cell device results under ideal dichroic splitting optics summing to 42Á7 W 2Á5% are described.

A direct-bonded GaAs/ InGaAs solar cell is demonstrated. The direct-bonded interconnect between subcells of this two-junction cell enables monolithic interconnection without threading dislocations and planar defects that typically arise during lattice-mismatched epitaxial heterostructure growth. The bonded interface is a metal-free n + GaAs/ n + InP tunnel junction. The tandem cell open-circuit voltage is approximately the sum of the subcell open-circuit voltages. The internal quantum efficiency is 0.8 for the GaAs subcell compared to 0.9 for an unbonded GaAs subcell near the band gap energy and is 0.7 for both of the InGaAs subcell and an unbonded InGaAs subcell, with bonded and unbonded subcells similar in spectral response.

We have fabricated devices with the structure InP/In 0.53 Ga 0.47 As/InP, with a InGaAs doping range varying from 2ϫ10 14 to 2ϫ10 19 cm Ϫ3. These isotype double heterostructures were doped both n and p type and were used to measure the minority-carrier lifetime of InGaAs over this doping range. At the low doping end of the series, recombination is dominated by the Shockley-Read-Hall effect. At the intermediate doping levels, radiative recombination is dominant. At the highest doping levels, Auger recombination dominates as the lifetime varies with the inverse square of the doping concentration. From fitting these data, the radiative-and Auger-recombination coefficients are deduced.

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We use confocal photoluminescence microscopy to study carrier diffusion near an isolated extended defect (ED) in GaAs. We observe that the carrier diffusion length varies non-monotonically with carrier density, which we attribute to competition between point defects and the extended defect. High density laser illumination induces a permanent change in the structure of the extended defect, more significantly an apparent change in the effective polarity of the defect, and thus a drastic change in its range of influence. The inferred switch of principal diffusing species leads to a potential design consideration for high injection optoelectronic devices.

Hydrogen-induced exfoliation combined with wafer bonding has been used to transfer ϳ600-nm-thick films of ͑100͒ InP to Si substrates. Cross-section transmission electron microscopy ͑TEM͒ shows a transferred crystalline InP layer with no observable defects in the region near the bonded interface and an intimately bonded interface. InP and Si are covalently bonded as inferred by the fact that InP/Si pairs survived both TEM preparation and thermal cycles up to 620°C necessary for metalorganic chemical vapor deposition growth. The InP transferred layers were used as epitaxial templates for the growth of InP/In 0.53 Ga 0.47 As/InP double heterostructures. Photoluminescence measurements of the In 0.53 Ga 0.47 As layer show that it is optically active and under tensile strain, due to differences in the thermal expansion between InP and Si. These are promising results in terms of a future integration of Si electronics with optical devices based on InP-lattice-matched materials. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1637429͔Applications of InP-based materials are numerous, and thus integration of InP on Si may enable realization of powerful integrated III-V-on-Si systems. InP and its lattice matched quaternary counterpart In 1Ϫx Ga x As y P 1Ϫy are direct gap semiconductors, which have high carrier mobilities, therefore finding applications in lasers, multijunction solar cells 1 and high-speed devices. Additionally, they cover the low dispersion and minimum loss wavelengths for optical fiber communication at 1.3 and 1.5 m, respectively, making them attractive materials for fabricating semiconductor lasers and detectors for telecommunications applications. However, InP is mechanically fragile, is not available in large substrates, and is expensive. Integrating InP thin films on Si substrates improves its mechanical strength and may also allow InP integration on large substrates by a process of tiling transferred thin films. Most importantly, a viable approach to InP/Si may enable cost-effective integration of infrared optoelectronic devices with well-established silicon electronics.Because InP and Si have a large lattice mismatch ͑8.1%͒, heteroepitaxial growth on Si has not yet been able to produce the high quality electronic material needed in optoelectronic devices, since the dislocation density is typically 10 7 cm 2 . 2In some cases densities of 10 5 cm Ϫ2 can be reached by conformal growth, but this is only possible on very small areas. 3 Other methods have been attempted to circumvent the restrictions of heteroepitaxial growth. However, most of these processes require an entire substrate to be consumed. 4 Direct wafer bonding of III-V semiconductors to Si has been previously demonstrated. 5,6 However, it would be more desirable to have a method for InP/Si integration in which the InP substrate can be repeatedly reused, rather than consuming one InP substrate per active InP-based device layer. Hydrogen-induced exfoliation and layer transfer has shown to be a successful method for Si film fabrication, ...

We have designed, fabricated, and tested a small, integrated photovoltaic module comprised of two separately‐contacted, high efficiency, multijunction solar cells and non‐imaging optics that both concentrate and spectrally split the incoming light. This hybrid design allows us to individually optimize the tandem cells and optical elements. The system has a measured module efficiency, including optical and packaging losses but not power combination losses, of 38.5 ± 1.9% under the AM1.5 direct terrestrial spectrum. The internal optics concentrate the light by a factor of approximately 20. We find excellent agreement between the modeled and measured performance. This is the highest confirmed conversion efficiency demonstrated for a photovoltaic module. Copyright © 2010 John Wiley & Sons, Ltd.