Crystallography and optical energy gap values for Cd 2 x(CuIn) yMn 2 zTe 2 alloys

Abstract

Polycrystalline samples of Cd 2 x (CuIn) y Mn 2 z Te 2 ( x + y + z = 1) alloys were prepared by a melt and anneal technique. Debye-Scherrer X-ray powder photographs were used to determine equilibrium conditions and lattice parameter values. It was found that in addition to the zinc blende and chalcopyrite structures, a partially ordered cubic structure was obtained, plus a two-phase field at higher z values. Room-temperature measurements of optical absorption were made to give values of the optical energy gap E g for all single phase samples. It was found that the variation of a was practically linear with composition and so could not be used to determine the boundaries between the three different phase fields. However, while E g varied linearly with composition inside a phase field, the resulting lines had different aiming points at z = 1, the values being 2.83 eV for zinc blende, 1.90 eV for the ordered cubic phase, and 1.36 eV for the chalcopyrite phase. Thus the values of E g give a very good indication of the phase boundaries.