Improving Electrical Properties by Effective Sulfur Passivation via Modifying the Surface State of Substrate in HfO₂/InP Systems

The thermal stabilities and interfacial properties of HfO₂ films created on conditioned i-InP surfaces using atomic layer deposition were investigated. When HfO₂ was deposited on sulfur passivation InP substrate, improved interfacial properties and electrical properties were observed by suppressing the interfacial oxides and In or P dangling bonds between HfO₂ and InP. X-ray photoelectron spectroscopy (XPS) and thermodynamic data indicated that the acetone-methanol-Isopropanol (AMI) pre-clean process on InP substrate before sulfur treatment helps a sulfur passivation layer on the InP surface form more effective, in comparison to hydrogen fluoride (HF) pre-cleaning. HF pre-cleaning reduces InP native oxides effectively, but In-F bonds are generated on the InP surface, which interrupts the formation of In-S bonds. Moreover, total density of states (TDOS) and electron localization function (ELF) calculation data showed that In-F bonds do not significantly decrease midgap defect states induced by the In dangling bond because fluorine does not chemically bond with In atoms. As a result, the AMI pre-clean process was proposed for effective S passivation on the substrate in the HfO₂/InP system. The capacitance-voltage (C-V) data revealed that the hysteresis width and frequency dispersion in the C-V accumulation and depletion were significantly improved in the AMI+S treated sample, as compared with the HF+S treated sample. In addition, the AMI+S treated HfO₂/InP showed excellent thermal stability for the interfacial, structural, and electrical properties during post annealing at 600 °C.