Direct vs. indirect optical recombination in Ge films grown on Si substrates

The optical emission spectra from Ge films on Si are markedly different from their bulk Ge counterparts. Whereas bulk Ge emission is dominated by the material's indirect gap, the photoluminescence signal from Ge films is mainly associated with its direct band gap. Using a new class of Ge-on-Si films grown by a recently introduced CVD approach, we study the direct and indirect photoluminescence from intrinsic and doped samples and we conclude that the origin of the discrepancy is the lack of self-absorption in thin Ge films combined with a deviation from quasi-equilibrium conditions in the conduction band. The latter is confirmed by a simple model suggesting that the deviation from quasi-equilibrium is caused by the much shorter recombination lifetime in the films relative to bulk Ge

Experimental Study on CH⁺ Formation from Doubly Charged Carbon and Molecular Hydrogen

We studied the reaction of doubly charged carbon C2+ (C iii) with molecular hydrogen, a possible source of the high, unexplained abundances of interstellar CH+. The experiment was carried out using the cryogenic linear 22-pole radio frequency ion trap. The measured reaction rate coefficient amounts to (1.5 0.2) x 10(-10) cm(3) s(-1), nearly independently of the covered temperature range from 15 to 300 K. In the product distribution study, the C+ ion was identified as the dominant product of the reaction. For the CH+ production, we determine an upper limit for the reaction rate coefficient at 2 x 10(-12) cm(3) s(-1)

Binary and ternary recombination of D-3(+) ions with electrons in He-D-2 plasma

An experimental study is reported about the recombination of D-3(+) ions with electrons in a low-temperature plasma (200-300K) consisting of He with a small admixture of D-2. At several temperatures, the pressure dependence of the apparent binary recombination rate coefficient (alpha(eff)) was measured over a broad range of helium pressures (200-2000 Pa). The binary and ternary recombination rate coefficients were obtained from measured pressure dependences of alpha(eff). The binary recombination rate coefficient obtained alpha(bin)(300 K) = (2.7 +/- 0.9) x 10(-8) cm(3) s(-1) is in agreement with recent theory. The ternary recombination rate coefficient obtained is K-He(300 K) = (1.8 +/- 0.6) x 10(-25) cm(6) s(-1). In analogy with the recently described process of helium-assisted ternary recombination of H-3(+) ions, it is suggested that the ternary helium- assisted recombination of D-3(+) ions proceeds through the formation of a neutral long- lived highly excited Rydberg molecule D-3 followed by a collision with a He atom

Advances in Dilute Nitride Multi-Junction Solar Cells for Space Power Applications

A sub-cell with bandgap of around 1 eV is required to improve the efficiency of multi-junction solar cells beyond what is possible with legacy triple-junction architectures [1]. Solar Junction Corporation has been focused since 2007 on the development and commercialization of dilute nitride materials to be used as the 1eV sub-cell in a fully lattice matched multijunction solar cell. Initial focus on the terrestrial concentrating photovoltaics (CPV) market led to Solar Junction Corp.’s achievement of multiple world records in multi-junction solar cell efficiency with its triplejunction cells on GaAs [2], [3]. These solar cells have been available as commercial products since 2010. Solar Junction Corp. has leveraged its high-quality, manufacturable dilute nitride material to develop and introduce an entirely new class of space solar cells capable of reaching over 33% AM0 conversion efficiency in a four-junction (4J) configuration lattice matched to active Ge substrates, with a clear line of sight to 36% AM0 efficiency in five- or six-junction devices that can be manufactured more cost-effectively than devices relying on metamorphic technologies. In this paper, we review the latest performance and qualification results of Solar Junction Corp.’s lattice matched 4J-on-Ge space solar cells and CIC (Cell- Interconnect-Coverglass) products incorporating GaInNAsSb dilute nitride material. We also report on the production readiness of these advanced space solar cells manufactured using an optimized hybrid Molecular Beam Epitaxy (MBE) / Metal Organic Vapor Phase Epitaxy (MOVPE) growth process

Advances in Dilute Nitride Multi-Junction Solar Cells for Space Power Applications

A sub-cell with bandgap of around 1 eV is required to improve the efficiency of multi-junction solar cells beyond what is possible with legacy triple-junction architectures [1]. Solar Junction Corporation has been focused since 2007 on the development and commercialization of dilute nitride materials to be used as the 1eV sub-cell in a fully lattice matched multijunction solar cell. Initial focus on the terrestrial concentrating photovoltaics (CPV) market led to Solar Junction Corp.’s achievement of multiple world records in multi-junction solar cell efficiency with its triplejunction cells on GaAs [2], [3]. These solar cells have been available as commercial products since 2010. Solar Junction Corp. has leveraged its high-quality, manufacturable dilute nitride material to develop and introduce an entirely new class of space solar cells capable of reaching over 33% AM0 conversion efficiency in a four-junction (4J) configuration lattice matched to active Ge substrates, with a clear line of sight to 36% AM0 efficiency in five- or six-junction devices that can be manufactured more cost-effectively than devices relying on metamorphic technologies. In this paper, we review the latest performance and qualification results of Solar Junction Corp.’s lattice matched 4J-on-Ge space solar cells and CIC (Cell- Interconnect-Coverglass) products incorporating GaInNAsSb dilute nitride material. We also report on the production readiness of these advanced space solar cells manufactured using an optimized hybrid Molecular Beam Epitaxy (MBE) / Metal Organic Vapor Phase Epitaxy (MOVPE) growth process