We report on multijunction GaInP/GaAs photovoltaic cells with efficiencies of 29.5% at 1-sun concentration and air mass (AM) 1.5 global and 25.7% 1-sun, AM0. These values represent the highest efficiencies achieved by any solar cell under these illumination conditions. Three key areas in this technology are identified and discussed; the grid design, front surface passivation of the top cell, and bottom surface passivation of both cells. Aspects of cell design related to its operation under concentration are also discussed.

A two-terminal, monolithic cascade solar cell with an efficiency of 27.3% is reported. The device structure consists of a Ga0.5In0.5P homojunction grown epitaxially upon a GaAs homojunction, with a GaAs tunnel diode interconnect. The tandem combination of these two materials is lattice matched, and has a theoretical efficiency of 34%. The device was grown by metalorganic chemical vapor deposition at 700 °C, using trimethylgallium, trimethylindium, arsine, and phosphine as sources. The minority-carrier transport properties of the Ga0.5In0.5P are shown to be relatively insensitive to variations of the growth temperature and phosphine overpressure. Other factors that affect the efficiency of the device are presented and discussed.

Using time-resolved photoluminescence, we have examined the optoelectronic properties of Ga0.5In0.5P/GaAs/Ga0.5In0.5P double heterostructures grown by organometallic chemical vapor deposition. For comparison, similar structures using Al0.4Ga0.6As/GaAs and Al0.5In0.5P/GaAs lattice-matched heterointerfaces were also examined. For the Ga0.5In0.5P/GaAs heterostructure, we show that the recombination velocity at a Ga0.5In0.5P/GaAs interface can be less than 1.5 cm/s. As a result, photoluminescence decay times as long as 14 μs have been observed in undoped GaAs double heterostructures. This photoluminescence decay time varies with temperature as T1.59, characteristic of radiative recombination not limited by surface or bulk nonradiative recombination processes. For the Al0.4Ga0.6As/GaAs and Al0.5In0.5P/GaAs heterostructures examined in this study, the upper limits of the interface recombination velocity were 210 and 900 cm/s, respectively.

We present the first experimental evidence for the spontaneous breaking of cubic symmetry in the band structure of films of Gao.52Ino.4sP grown by organometallic-vapor-phase epitaxy on (100) GaAs substrates. We show how this effect is related to the spontaneous ordering of the alloy, and its correlation with the anomalous lowering of the band gap observed in these films. PACS numbers: 78.55.Cr, 61.50.Ks, 61.55.Hg, 71.70.Ch Spontaneous long-range ordering into the CuAul, CuPt, and chalcopyrite structures has recently been observed in several normally disordered isovalent III-V alloys A x B\x C lIn the case of the alloy GaInP2 grown by organometallic-vapor-phase epitaxy (OMVPE) on (001) GaAs substrates, electron-diffraction studies reveal ordering of the cations on the group-Ill sublattice along [Til] or [ill], two of the four (lll)-type directions (see Fig. 1 ). 2~5 A mechanims for this spontaneous long-range ordering has been proposed. 6 This mechanims consists of the following: (1) the alignment of Ga and In atoms into a series of alternate [110]-direction Ga-atom lines within each (001) plane, which is caused by the anisotropic site occupation affinity for column-Ill atoms because of their large bond-length difference, and the asymmetry in the direction for the dangling bonds;(2) the in-phase alignment of two Ga lines belonging to adjacent (OOl)-ordered planes, which is caused by the selective settling of Ga atoms on the (111)2? microfacets of [110] step arrays. Thus, although bulk GaInP2 is metastable 7 with respect to phase separation, the longrange ordering observed during epitaxial growth is a result of surface thermodynamic effects rather than bulk

No abstract