Defects in HgTe and CdHgTe Grown by Molecular Beam Epitaxy

Abstract

The defect morphology in HgTe and CdHgTe was studied in (211)B-oriented layers grown in a 20°C temperature range around the optimal growth temperature. The density of defects varies strongly with the growth temperature. In HgTe, the shape of the microvoid defects is very sensitive to the growth temperature and can be used to determine the deviation from the optimal growth temperature. Using thermodynamical modeling, the optimal growth temperature for CdHgTe can then be calculated. We describe a mechanism for the formation of microvoids and needles which involves preferential surface diffusion of Te combined with an impurity or defect on the substrate. Microvoids on (111)B-oriented partially twinned HgTe layers were also studied. The microvoids in the twinned parts of the layer were found to be rotated 180 deg relative to the untwinned parts of the layer.

The Effects of Microvoid Defects on MWIR HgCdTe-Based Diodes

“…They have not been described on (001) or similar surfaces, where pyramidal hillock defects are the dominant defect type. Microvoid and similar defects have been described in several previous studies, [1][2][3][4][5][6][7] using a variety of distinct terms including voidhillock complex, 5 triangle defects, 6 etc. These previous studies, while using varying terminology and characterization techniques, seem to describe a single class of defects with the following characteristics:…”

“…While the exact cause of the observed microvoid defects is not known, it is believed they are due to one of the mechanisms mentioned above and more fully discussed in Ref. 1.…”

“…The structure of the microvoid is again distinct from the void, which is typically deeper, and may or may not be filled with polycrystalline material. 1,2 Often, but not always, microvoids are associated with clusters, or nesting of dislocations, as revealed by decoration etching, whereas void defects are not typically associated with such clusters. 5,7 There is no consensus on the cause of these defects, with various explanations having been offered, including Hg-rich growth conditions, 1,2 temporal variations in growth conditions, 5 and substrate-originated defects.…”

Molecular Beam Epitaxy Growth of Nanowires in the Hg1-xCdxTe Material System

“…Some Si substrates were covered with a photoresist mask (for example an array of 3.5-μm-diameter holes) and the HF etch repeated before Au sputtering, resulting in Au particles in defined areas only. MBE growth of HgTe and HgCdTe thin films of high crystalline quality requires controlling the substrate temperature to within ± 1 o C of the optimum growth temperature, which is just below the Te-phase limit (onset of Te precipitation) (Colin & Skauli, 1997;Selvig et al, 2007;Selvig et al 2008a;Selvig et al, 2008b and much lower deposition rates (would give equivalent thin film growth rates in the range 1-100 Å/min). The equivalent film thickness deposited was varied from 20 Å to 0.5 μm in order to investigate how the nanowires evolve during growth.…”

HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization

“…[1][2][3] We have found how these vary with deviation from the optimal growth temperature T opt . A grown layer of HgTe can function as an in situ thermometer for establishing and maintaining the highly critical substrate temperature calibration: the shape and density of the microvoids in HgTe give the deviation from T opt , and thermodynamic calculations relate this to T opt for Hg 1Àx Cd x Te with any Cd mole fraction x-value.…”