GaInSb and GaInAsSb thermophotovoltaic device fabrication and characterization

Abstract

DISCLAIMERAbstract Thermophotovoltaic (TPV) devices have been fabricated using epitaxial ternary and quaternary layers grown on GaSb substrates. The GaInSb layers were grown by organometallic vapor phase epitaxy (OMVPE) and the InGaAsSb lattice-matched layers were grown by liquid phase epitaxy (LPE) . Device fabrication steps include unannealled ptype ohmic contacts, annealed Sn/Au n-type ohmic contacts, and a thick Ag topsurface contact using a lift-off process. Devices are characterized primarily by dark I-V, photo I-V, and quantum efficiency measurements, which are correlated to microscopic and macroscopic material properties. Particular emphasis has been on material enhancements to increase quantum efficiency and decrease dark saturation current density. TPV device performance is presently limited by the base diffusion length, typically 1 to 2 microns. IntroductionThis paper presents the fabrication and characterization of ternary (GaInSb) and quaternary (GaInAsSb) device layers grown on GaSb substrates, extending earlier results [l]. For current devices, all active layers have bandgaps in the 0.52eV to 0.56eV range. The lattice constants of the ternary structures are, of necessity, not matched to that of the binary (GaSb). However, the added complexity of the fourth element (As) in quaternaries allows matching the lattice constant of the epilayers to the substrate while varying the bandgap. The epitaxial growth conditions and characterization of the epitaxial material are presented elsewhere [2]. Here the fabrication and characterization of thermophotovoltaic devices using the epitaxial layers as starting material are presented. Epitaxial Structures and Junction ProcessingBoth ternary (GaInSb) and quarternary (GaInAsSb) epitaxial layers grown on GaSb substrates have been used in fabricating and characterizing p-n junctions for TPV applications. The ternary device structures were produced by OMVPE, with the quaternary device structures produced by LPE. The junctions that have been fabricated and characterized are grouped into three "generations," corresponding to the general time frame of fabrication. The ternary device structures are shown in figure 1. These generation 1 and generation 2 structures were initial structures with parameters chosen primarily based upon preliminary material studies and first-order device design. The generation 3 structure, however, contains layers with variable thicknesses and dopings in order to study the effects of individual parameter variations on device performance. In all three cases, the grown epi-layers were not lattice matched to the underlying GaSb. A series of graded layers varying from Gal.oIno.oSb at the substrate to the approximately Gao.8Ino.2Sb of the device region, separate the substrate from the base region.The quaternary device structures shown in figure 2 were fabricated by LPE. Generation 1 and 2 were identical except that generation 1 relied upon parasitic gallium anti-site defects for emitter doping, while the generation 2 emitter was doped with germanium...

A multi-color quantum well photodetector for mid- and long-wavelength infrared detection

“…Such alloys have opened up new generations of device applications in recent decades by dramatically increasing the possibilities for engineering the material properties [1]. These materials exhibit a wide band gap, ranging from infrared (IR) to visible light, which is useful for applications in thermo-photovoltaic [3], optoelectronics [4] and high-speed devices [5]. Several works have been focused on the elaboration of binary, ternary and especially quaternary alloy epitaxial layers and then on the investigation of their optical and physico-electrical properties [6].…”

“…In A 1−x B x C y D 1−y alloys, the two compositions x and y can be modulated and each set of values (x, y) corresponds to an operating wavelength of a particular device [6]. The 3 Author to whom any correspondence should be addressed. importance of quaternary alloys lies in the fact that both energy band gap and lattice parameter can be varied independently.…”