Lattice-Mismatched InGaAsP and AlGaInAs Quaternary Materials for Thermophotovoltaic Applications

Experimental results are presented for lattice-mismatched (LMM) In _0.8Ga_0.2As_0.76P_0.24 and Al _0.07Ga_0.255In_0.675As quaternary materials used in thermophotovoltaic (TPV) devices. Epistructures were grown on 3-inch diameter InP substrates by metalorganic vapor phase epitaxy (MOVPE) and processed as monolithically interconnected modules (MIMs) using conventional photolithography and chemical wet etching. Electrical characterization of single-bandgap quaternary devices revealed that the two have roughly equivalent electrical performance. Comparable X-ray diffraction data, high voltage factors and fill factors indicate the materials are of high crystalline and electrical quality, and perform comparably to expectations set by long experience with 0.6 eV lattice-mismatched InGaAs devices of similar device design. Integration of the high and low bandgaps into tandem devices has proven problematic, however, suggesting unresolved materials and processing issues