Polycrystalline GaAs for large area imaging detectors

Epitaxial layers of GaAs, when thick enough, are now recognized as good candidates for X-ray imaging. In order to overcome the limitation in the size of the substrates for large imaging applications, we are developing a growth technique by chemical reaction which allows to obtain several hundred microns thick polycrystalline layers, i.e. of unlimited dimensions, in few hours. The size and orientation of the grains can be controlled to some extent through the growth conditions. We shall present data concerning optical (IR absorption, luminescence), structural (double X-ray diffraction) and electrical (resistivity, current–voltage characteristics of Schottky barriers) characterizations performed on 300 μm thick non-intentionally doped layers in which the crystallites, of columnar structure, are 〈1 1 1〉 oriented and of diameter 70±10 μm. We now aim at controlling the location of the crystallites on the glass substrate in order to get a regular pattern and at resuming a new epitaxy on a polycrystalline surface.