Interface characterisation of ZnSe/CuGaSe 2 heterojunction

Abstract

The ZnSe/CuGaSe 2 heterojunctions were fabricated by flash evaporation technique of CuGaSe 2 onto the (110) surface of ZnSe crystals. CuGaSe 2 layers had thickness ∼2–4 μm and showed a hole concentration up to (1.5–18.0)×10 18 cm −3 and mobility μ∼4–24 cm 2 V −1 s −1 at 300 K. The charge carrier concentration in ZnSe crystals at 300 K was n=5.6×10 16 cm −3 and their mobility μ=300 cm 2 V −1 s −1. The investigated ZnSe/CuGaSe 2 heterojunctions have at the interface an intermediate layer with a thickness of ∼450–750 Å and a linear graded band gap as well as an i-ZnSe compensated layer with a thickness of ∼1–2 μm and resistivity ρ∼10 8–10 9 Ω cm. The i-ZnSe layer is highly compensated due to the presence of Cu acceptor impurities. In this layer the Fermi level position E c− F 0∼690 meV and a trap level position E t− F 0∼17 meV were determined. The total trap concentration in the i-ZnSe layer is N t∼5×10 14 cm −3. The mean free path of excited charge carriers in the graded band gap region was calculated as λ∼55 Å. On the basis of experimental data analysis of electrophysical properties of both ZnSe/CuGaSe 2 heterojunctions and constituent materials the energetic band diagram of the investigated heterostructures is proposed. The current transport mechanism through ZnSe/CuGaSe 2 heterojunctions is consequently elucidated.