M. Martinka

Improved morphology and crystalline quality of MBE CdZnTe/Si

We report on continuing efforts to develop a reproducible process for molecular beam epitaxy of CdZnTe on three-inch, (211) Si wafers. Through a systematic study of growth parameters, we have significantly improved the crystalline quality and have reduced the density of typical surface defects. Lower substrate growth temperatures (∼250–280°C) and higher CdZnTe growth rates improved the surface morphology of the epilayers by reducing the density of triangular surface defects. Cyclic thermal annealing was found to reduce the dislocation density. Epilayers were characterized using Nomarski microscopy, scanning electron microscopy, x-ray diffraction, defect-decoration etching, and by their use as substrates for HgCdTe epitaxy.

Characterization of cross-hatch morphology of MBE (211) HgCdTe

We present the results of a detailed study of the nature and origin of cross-hatch patterns commonly observed on (211) HgCdTe epilayers deposited by molecular beam epitaxy. Cross-hatch patterns were examined using x-ray topography as well as Nomarski, interferometric, and atomic force microscopies. Cross-hatch patterns were generally comprised of three sets of lines, parallel to the [231],, [213], and [011] directions. The lines parallel to the [011] direction exhibited distinct properties compared to the two sets of lines parallel to [231] and [213]. Under growth conditions characterized by excessive Hg flux (low temperature), lines parallel to [011] were periodic and tended to dominate the cross-hatch pattern. In some cases, bands of dislocations, 10–100 m in width, formed parallel to [011]. Under optimized growth conditions, on very closely lattice-matched substrates, (dislocation densities <105 cm−2) lines parallel to [011] vanished entirely, and lines parallel to [231] and [213] became sparse. The remaining lines were typically fragments terminated by either a single dislocation, a cluster of dislocations (micro-void), or the wafers edge. The density of these line fragments tended to decrease as the dislocation density decreased. Under the best growth conditions on very closely lattice-matched substrates we have achieved dislocation densities of 5 104 cm−2, which is comparable to the dislocation density of the CdZnTe substrate.

Two-dimensional molecular beam epitaxy of {001} Cdte on Cd and Zn terminated {001} GaAs

Amorphous layers of CdTe deposited on Cd or Zn terminated GaAs {001} surfaces can be recrystallized above ∼200°C. Subsequent molecular beam epitaxy of CdTe proceeds in a two-dimensional mode and leads to layers which are specular and single domain {0011}. Threading dislocation density in these layers was 1–2 x 105 cm−2. Values of full width at half maximum for x-ray rocking curves were as low as 80 arc-s.

Selected‐area epitaxy of CdTe

Selected‐area epitaxy of CdTe grown by chemical‐beam epitaxy and migration‐enhanced epitaxy was achieved at reduced temperatures (above 225 °C) on (001) GaAs substrates patterned with SiO2. CdTe single‐crystal growth was observed on the GaAs surface while no deposition was detected on the SiO2. Selected epitaxy was further demonstrated in reduced‐area patterns with dimensions suitable for the monolithic integration of infrared focal plane and processor arrays. Growth selectivity was confirmed by scanning Auger microscopy, scanning electron microscopy, reflection high‐energy electron diffraction, and x‐ray double‐crystal rocking curve analysis. A method is proposed to reduce the growth temperature to below 200 °C; a temperature appropriate for epitaxy of device‐quality HgCdTe.