Analysis of the electrical and luminescent properties of CuInSe2

Abstract

We discuss the electrical properties and the luminescence spectra of CuInSe₂ melt−grown single crystals as a function of the growth and annealing conditions, and the presence of extrinsic dopants such as Zn or Cd. We find that crystals grown from melts containing a slight Se excess or annealed under maximum Se pressure are p type, whereas crystals grown from excess In melts or annealed under minimum Se pressure (vacuum) are n type. The low−temperature photoluminescence spectra of crystals as−grown or annealed between 400 and 700 °C are characteristic of the conductivity type. At 77 °K, p−type crystals emit in a band peaked at 1.00 eV (type A spectrum), whereas the emission of n−type crystals peaks at 0.93 eV (type B spectrum). Types A and B spectra can be interchanged by alternate anneals in minimum or maximum Se pressure. Type B emission dominates the electroluminescence spectrum of p−n junctions. A sharp band−to−band emission at 1.04 eV is present in the 77 °K photoluminescence spectrum of some high−resistivity samples, confirming that the material has a direct band gap. We find that Zn and Cd are donors. Crystals doped with these impurities have electron concentrations above 10¹⁸ cm⁻³. Zn−doped samples exhibit a very broad photoluminescence band below the band gap at both 77 and 300 °K.