MICROSTRUCTURAL DEFECT REDUCTION IN HGCDTE GROWN BY PHOTOASSISTED MOLECULAR-BEAM EPITAXY

Twinning defects are a severe problem encountered in the growth of HgCdTe by molecular-beam epitaxy on the (100) and (111) orientations. The presence of these defects is a major potential source of noise generation in long-wavelength infrared HgCdTe detectors. Thus, the reduction of microstructural twin defects in the preparation of HgCdTe is of great importance. By tightly controlling the Hg overpressure and substrate temperature during photoassisted molecular-beam epitaxy growth of HgCdTe epilayers, a reduction of these microscopic twin defects has been achieved. In particular, pyramidal hillocks and facets on the (100) orientation of HgCdTe were reduced to lXlO cm-2. In-plane twin domains were eliminated for (lll)B HgCdTe films grown within a stringent parameter space. However, the demanding parameter control resulted in limited yields of twin free material. A new growth approach, compositionally modulated structures, has been developed in an attempt to increase the yield of twin free (111) B HgCdTe films. This approach involves the growth of thin CdTe epilayers spaced periodically throughout the HgCdTe matrix followed by an interdiffusion step. The films were characterized by defect etch, x-ray diffraction, and transmission electron microscopy. Films grown by this technique exhibited an absence of laminar twin defects as well as etch pit density counts comparable to that obtained from excellent liquid phase epitaxy. © 1990, American Vacuum Society. All rights reserved.