Optical transitions near the band edge in bulk CuInxGa1-xSe2 from ellipsometric measurements

From the analysis of the variation of optical absorption coefficient cr wit h incident photon energy between 0.8 and 2.6 eV, obtained from ellipsometri c data, the energy E-G of the fundamental absorption edge and E'(G) of the forbidden direct transition for CuInx Ga1-x Se-2 alloys are estimated. The change in E-G and the spin-orbit splitting Delta (SO) = E'(G) - E-G with th e composition x can be represented by parabolic expression of the form E-G( x) = E-G(0) + ax + bx(2) and Delta (SO)(x) = Delta (SO)(0) + a'x + b'x(2), respectively. b and b' are called "bowing parameters". Theoretical fit give s a = 0.875 eV, b = 0.198 eV, a' = 0.341 eV and b' = -0.431 eV. The positiv e sign of b and negative sign of b' are in agreement with the theoretical p rediction of Wei and Zunger . (C) 2001 Elsevier Science B,V. All rights res erved.