Substrate-based catalytic growth modes have been widely used to fabricate vertically aligned nanowires for most technologically relevant semiconducting systems, with CdTe being a notable exception. The catalysts that promote a one-dimensional nanoscale growth mode in other systems seem to fail, creating the need for an alternative approach. Here, we demonstrate how nanowire structures can be derived from a newly developed catalytically driven process. The vertically aligned nanowires produced are highly faceted and share an epitaxial relationship with the underlying substrate. The nanowire structures could also be described as nanorods; they show a high degree of size uniformity over large areas with heights of 300 nm imposed by growth dynamics. Two-dimensional x-ray diffraction techniques indicate that the CdTe exists in the wurtzite crystal structure instead of the zinc blende structure normally associated with the bulk material. The work presented here adds these substrate-based wurtzite CdTe nanowires to the growing list of potential building blocks for nano-based devices.

A combination of Raman scattering and cathodoluminescence techniques has been used to study the spatial distribution of Te precipitates in the volume of CdTe wafers. Starting with the as-grown crystals with random distribution of precipitates over the whole volume, improvement at different stages of thermal annealing is demonstrated. As-grown p-CdTe wafers were annealed at 500–600  °C either in Ga melt or in Cd vapor for 2 or 22 h. The kinetics of dissolution of Te precipitates was found to be similar for both the Ga melt and Cd vapor annealing processes. Short-time annealing causes the disappearance of small Te precipitates, while the larger ones, 5–10 μm in size which decorate the extended structural defects, still remain. After a long-time annealing, the complete disappearance of Te precipitates occurs in the wafers volume. Interestingly, it was observed that the disappearance of Te precipitates during annealing starts in the central part of the bulk wafer and is followed by a precipitate gettering at the wafer surface. This implies that it is possible to obtain precipitate-free CdTe wafers by postgrowth annealing.

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Defect levels in CdTe doped with Bi are studied by low temperature photoluminescence, photoinduced current transient spectroscopy, photoconductivity measurements, and optical absorption. Two centers associated with the doping with Bi are reported. The first one, a deep level located at E v + 0.71 eV, only present at low dopant concentrations, has donor character and hole-trap properties, and is mainly responsible for the high resistivity and very high photoconductivity of the samples. The second one, an acceptor center located at E v + 0.30 eV, assigned to Bi Te species, is only present at high dopant concentrations and is mainly responsible for the low resistivity and poor photoconductivity of these samples.

Cathodoluminescence (CL) microscopic techniques have been used to study the spatial distribution of structural defects and the deep levels in CdTe:Ge bulk crystals. The effect of Ge doping with concentrations of lOI7 and 1019 cmW3 on the compensation of V,, in CdTe has been investigated. Dependence of the intensity distribution of CL emission bands on the dopant concentration has been studied. Ge doping causes a substantial reduction of the generally referred to 1.40 eV luminescence, which is often present in undoped CdTe crystals, and enhances the 0.91 and 0.81 eV emissions. 0 199.5 American Institute of Physics.