Optical absorption and photoluminescence in the ternary chalcopyrite semiconductor AgInSe2

Optical-absorption and photoluminescence (PL) spectra have been measured on the ternary chalcopyrite semiconductor AgInSe2 at T=13–300K. The direct-band-gap energy Eg of AgInSe2 determined from the optical absorption measurements shows unusual temperature dependence at low temperatures. The resultant temperature coefficient ∂Eg∕∂T is found to be positive at T<125K and negative above 125K. The PL spectra show asymmetric emission bands peaking at ∼1.18 and ∼1.20eV at T=13K, which are attributed to donor-acceptor pair recombinations between exponentially tailed donor states and acceptor levels. An energy-band scheme has been proposed for the explanation of the peculiar PL emission spectra observed in AgInSe2.