Modulating the band alignment and current conduction mechanism of ZrO2/In0.2 Ga0.8As gate stack by atomic-layer-deposited ZnO passivation layer

Abstract

Effect of an ultrathin ZnO interface layer (IL) on the band alignment and carrier transportation in atomic-layer-deposited ZrO2 high-k gate dielectrics on p-In0.2Ga0.8As substrates has been investigated. Based on x-ray photoelectron spectroscopy (XPS), the valence-band offset and conduction-band offset of ZrO2/ZnO bilayer with In0.2Ga0.8As are found to be 2.36 and 1.86 eV, respectively. Meanwhile, introducing ZnO IL has made the conduction-band offset increased by 0.26 eV as compared with monolayer ZrO2, thus remarkably suppressing the gate leakage current. It has been revealed by the current density-voltage characteristics measured from 27 °C to 102 °C that Schottky emission is dominant at low positive bias, while Ohm's law dominates the conduction mechanism at high positive bias for ZnO passivated p-In0.2Ga0.8As. However, for ZrO2/In0.2Ga0.8As, the leakage current follows Schottky emission at low positive bias and space-charge-limited conduction at high bias, which is in good agreement with the energy-band parameters extracted by XPS. The ZnO passivation dependent energy-band diagrams of the ZrO2/p-In0.2Ga0.8As heterostructures presented in this paper could be very valuable and beneficial for making ZrO2/ZnO/InGaAs great potential gate stacks in future III-V-based high-performance and low-power devices.