Isolation and control of voids and void-hillocks during molecular beam epitaxial growth of HgCdTe

Abstract

Void defects were demonstrated to form away from the substrate-epifilm interface during the molecular beam epitaxial growth of mercury cadmium telluride on cadmium zinc telluride substrates. These were smaller in size compared to voids which nucleated at the substrate-epifilm interface, which were also observed. Once nucleated, voids usually replicated all the way to the surface even if the flux ratios were modified to prevent additional nucleation of voids. Occasionally, void defects which close before reaching the top surface without leaving any perturbations on the surface, have also been observed. The voids which form away from the substrate-epi interface, nucleate on defects, frequently hillocks, introduced into the film already grown, leading to formation of defect complexes. These voids can be smaller than 1 µm and appear almost indistinguishable from unaccompanied simple voids. However, these void-hillock complexes displayed a nest of dislocations decorating these defects, which become apparent upon dislocation etching, whereas unaccompanied simple voids did not. The nests could extend as much as 25 µm from the individual void-hillock complex. The density of dislocations within the nest exceeded 5 x 10 6 cm -2 , whereas the dislocation density outside of the nest could decrease to < 2 x 10 5 cm -2 .

Physical structure of molecular-beam epitaxy growth defects in HgCdTe and their impact on two-color detector performance

“…As the Hg deficient environment continues, the void expands; altering the Hg constituent may prevent the voids from growing too large, but the crystallinity cannot be recovered, and the void remains throughout the growth. 6,7,9 Chandra et al 10 observed voids that were entirely contained below the surface; this was not observed in this study. Energy dispersive x-ray analysis (EDXA) has been performed on the cleaved sample ( Fig.…”

“…[2][3][4][5] Opportunities for performance improvement exist by reducing growth defects, in particular macrodefects such as voids, which can reduce FPA operability. Previous papers [6][7][8][9][10] have examined in depth the physical nature of voids and direct pixel-to-pixel correlation for single-color, mid-wavelength infrared (MWIR), MBE-grown HgCdTe/CdTe/Si FPAs. 11 However, direct correlation of defects to two-color device performance has not been investigated to date.…”

Surface Morphology and Defect Formation Mechanisms for HgCdTe (211)B Grown by Molecular Beam Epitaxy

“…Large void defects with sizes from several micrometers to tens of micrometers are the most common defect in MBE-grown HgCdTe. They arise as a consequence of Hg-deficient growth conditions, and are called either voids, 1,9,[40][41][42][43][44][45][46][47][48][49][50] crater defects, 6,10,22,23 V-shape 37 The directions of the crosshatched lines as well as the characteristic angles are labeled. The arrows show that the crosshatch lines are sometimes terminated by etch pits, namely dislocations in the crystal.…”

Nature of Growth Pits in Lead Salt Epilayers Grown by Molecular Beam Epitaxy

“…4,5 Although IV-VI semiconductors such as Pb 1-x Sn x Se show a high capability in comparison with II-VI and III-V materials, such as Hg 1-x Cd x Te and InSb, 6,7 not much effort has been devoted to exploring the full potential of IV-VI materials; for example, in the prevailing II-VI material, Hg 1-x Cd x Te, various growth defects have been identified such as dislocations, stacking faults and twins, voids and hillocks, as well as precipitates. [8][9][10] A similar study of the growth defects related to IV-VI materials, however, has not yet been implemented. This article will present an investigation of growth defects in PbSe epilayers grown by molecular beam epitaxy (MBE).…”