Majority and minority carrier traps in monocrystalline CulnSe2
Electron and hole traps in Bridgman-grown monocrystalline CuInSe2 were investigated by carrying out deep level transient spectroscopy measurements on homojunctions, Al-CuInSe2 (p-type), and Au-CuInSe2 (n-type) Schottky junctions. Three hole trap levels and two electron trap levels were observed on these devices. Effects of oxygen and etching on the electron trap level at 182 ±15 meV from the conduction band edge were specifically studied. It was found that the election trap densities in the homojunctions prepared using the CuInSe2 samples treated in NH2NH2 solution, which absorbes oxygen atoms in the samples, were larger than the electron trap densities in the homojunctions prepared using untreated samples. Moreover, the electron trap densities in the homojunctions after prolonged heat treatment in O2 were less than that without prolonged heat treatment. The results thus suggested that oxygen atoms in CuInSe2 can reduce the electron trap density of p-type CuInSe2. The effects of chemical etching on these electron traps were also studied. The excess indium atoms in the CuInSe2 were considered to affect the electron traps.