Modification of metal–InGaAs Schottky barrier behaviour by atomic layer deposition of ultra-thin Al2O3 interlayers

The effect of inserting ultra-thin atomic layer deposited Al₂O₃ dielectric layers (1 nm and 2 nm thick) on the Schottky barrier behaviour for high (Pt) and low (Al) work function metals on n- and p-doped InGaAs substrates has been investigated. Rectifying behaviour was observed for the p-type substrates (both native oxide and sulphur passivated) for both the Al/p-InGaAs and Al/Al₂O₃/p-InGaAs contacts. The Pt contacts directly deposited on p-InGaAs displayed evidence of limited rectification which increased with Al₂O₃ interlayer thickness. Ohmic contacts were formed for both metals on n-InGaAs in the absence of an Al₂O₃ interlayer, regardless of surface passivation. However, limited rectifying behaviour was observed for both metals on the 2 nm Al₂O₃/n-InGaAs samples for the sulphur passivated InGaAs surface, indicating the importance of both surface passivation and the presence of an ultra-thin dielectric interlayer on the current–voltage characteristics displayed by these devices.