T( z) Diagram and Optical Energy Gap Values of Zn 1- zMn zGa 2Se 4 Alloys

Abstract

The T( z) diagram of the system Zn 1- z Mn z Ga 2Se 4 was obtained from X-ray diffraction and differential thermal analysis measurements. It was found that at lower temperatures, a single phase solid solution occurs across the whole composition range and values of the lattice parameters were determined as a function of z. At higher temperatures, an order-disorder transition occurs to what is probably a partially ordered tetragonal structure when 0 < z < 0.83, and to a disordered defect zinc-blende structure when 0.83 < z < 1.0. In the T( z) diagram, it is found that all of the phase boundaries show discontinuities at z ≈ 0.83. Although the two terminal compounds have very similar tetragonal structures, they have different space group symmetries, and hence the discontinuities at z ≈ 0.83 are attributed to an abrupt change in space group symmetry at this composition. The values of the optical energy gap are found to show a similar discontinuity at the same composition. Two other similar alloy systems have recently been found to show similar behavior, and the results for the three systems are compared.