MOVPE growth of lattice-mismatched Al0.88In0.12As on GaAs (100) for space solar cell applications

We report, for the first time, the growth and characterization of lattice-m ismatched Al0.88In0.12As on GaAs (1 0 0) as part of a program to develop a high-efficiency, triple-junction space solar cell. The expected practical e fficiency of this cell is 31%. The proposed triple-junction cell consists o f a 2.1 -eV Al0.88In0.12As top cell, a 1.6 -eV In0.48Ga0.52As0.23P0.77 midd le cell, and a 1.2 -eV In0.13Ga0.87As bottom cell. The Al0.88In0.12As layer s were grown on GaAs(100) wafers cut 6 degrees off-axis. using metal organi c precursors trimethylaluminum, trimethylindium and the hydride arsine in a horizontal, reduced-pressure metal organic vapor-phase epitaxy (MOVPE) rea ctor. Crystalline quality was evaluated through triple-axis X-ray diffracto metry. Reciprocal lattice mapping showed that the Al0.88In0.12As layers wer e relaxed to a large extent, and were of high crystalline quality. Doping w as performed using silane (n-type) and diethylzinc (p-type). Secondary ion mass spectrometry (SIMS) and electrochemical C-V profiling showed that it w as possible to obtain abrupt doping profiles to the levels required for sol ar cell fabrication. Details of these results and those of dislocation dens ity measurement using transmission electron microscopy (TEM) are described in this paper. (C) 2000 Elsevier Science B.V. All rights reserved.