Effect of an inserted Al2O3 passivation layer for atomic layer deposited HfO2 on indium phosphide

Abstract

In this study, we demonstrate indium phosphide (InP) metal–oxide–semiconductor capacitors (MOSCAPs) with single HfO2 and stacked HfO2/Al2O3 dielectrics. Based on these capacitors, the effect of an inserted Al2O3 passivation layer with various thicknesses on the properties of InP MOSCAPs was further statistically investigated. By inserting a 2 nm thick Al2O3 passivation layer between high-κ HfO2 and the InP substrate, the characteristics including the frequency dispersion, leakage current and interface trap density (D it) were effectively improved, which could be attributed to the large bandgap of Al2O3 that suppressed substrate element diffusion and reduced oxidation of the InP substrate. A low D it of ∼3.8 × 1011 cm−2 eV−1 that was comparable to that of previously reported InP MOSCAPs was achieved. However, with the thickness of Al2O3 decreasing from 2 to 1 nm, the frequency dispersion and D it were slightly increased, because such an ultrathin Al2O3 layer could not effectively suppress the diffusion and may induce substrate oxidation after annealing. The present results show that the incorporation of an Al2O3 passivation layer with suitable thickness has great promise in future high-performance InP device applications.