Pressure dependence of band gaps in the quaternary semiconductors Cu(In,Ga)Se-2

Abstract

We report the photoluminescence and absorption spectra of a series of quaternary chalcopyrite alloys with the formula: CuIn1-xGaxSe2 where x varies between 0 and 1 in steps of 0.25. Using a diamond anvil cell we have studied their band gaps and impurity emission peak energies as a function of pressure. We found that while the band gap of CuIn1-xGaxSe2 varies nonlinearly with x the pressure coefficient (alpha) varies linearly with x at a rather large rate of d alpha/dx = 18.6 meV/GPa. We interpret our results in terms of recent theoretical calculations which have been proposed to explain the large difference in alpha between CuGaSe2 and CuInSe2.