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We report the Gao.861ii0.i4Aso.i3Sbo.87 room temperature refractive index value obtained from direct reflectivity measurements and also estimated from laser transversefar field pattern measurements. The value n = 3.78 obtained is higher than previous theoretical calculations and is high enough to support a good optical confinement in DII lasers with 27% Al in the confining layers. We also show that the active layer low resistivity gives the main contribution to the high threshold current (Ith) for narrow stripe lasers. This is partly solved by making the active region n-type. The minimum 'th obtained for n-type active layer lasers was 29OmA compared to 800mA for p-type active layer lasers, the broad area threshold current being the same (3kA/cm2) in both cases.

Characteristics of photovoltaic cells fabricated from diffused homojunctions in quaternary GalnAsSb are reported for the first time. The unique feature of these quaternary cells is the extended long-wavelength response to 2.2 mircons, enabling the efficient use of blackbody-like thermal sources operating as low as 1073 K in thermophotovoltaic energy conversion systems. Cells were based on a simple structure, and cell fabrication employed low-cost, high-yield, mature microelectronics processes. Specifically, Ga.88In.12As" 11 Sb.89 was grown by liquid-phase-epitaxy lattice matched to n-type GaSb substrates. The junction was formed by zinc doping in a quasi-closed-box diffusion furnace. Silicon nitride served as the anti-reflection coating, and electron-beam deposited metal contacts provided low resistance. Other salient features of these ceils include an internal quantum efficiency exceeding 75% at 299 K, and Voc --0.26 V, a fill factor of 0.55, and an Isc of 1.2 A/cm2, all at 288 K, excellent for a quaternary material whose optical characterization showed a bandgap of 0.58 eV. Process improvement can increase this fill factor to 0.75, as has been previously demonstrated with binary GaSb cells fabricated with similar processes.