  Cadmium Zinc Telluride and Cadmium Telluride are the detector materials of
choice for the detection of X-rays in the X-ray energy band E >= 5keV with
excellent spatial and spectral resolution and without cryogenic cooling. Owing
to recent breakthroughs in grazing incidence mirror technology, next-generation
hard X-ray telescopes will achieve angular resolution between 5 and 10 arc
seconds - about an order of magnitude better than that of the NuSTAR hard X-ray
telescope. As a consequence, the next generation of X-ray telescopes will
require pixelated X-ray detectors with pixels on a grid with a lattice constant
of <= 250um. Additional detector requirements include a low energy threshold of
less than 5keV and an energy resolution of less than one keV. The science
drivers for a high angular-resolution X-ray mission include studies and
measurements of black hole spins, the cosmic evolution of super-massive black
holes, active galactic nuclei feedback, and the behaviour of matter at very
high densities. In this contribution, we report on our R&D studies with the
goal to optimise small-pixel Cadmium Zinc Telluride and Cadmium Telluride
detectors.
