(Invited) Challenges in III-V Surface Passivation and Some Potential Solutions

Abstract

In many applications, III-V surfaces lie at the buried or embedded interface of an insulator/III-V or metal/III-V junction. The chemical and physical properties of these III-V interfaces are typically different from the uniform III-V bulk crystal structures. Thus, it is difficult to predict the interface behavior (e.g. electronic structure and doping efficiency) on the basis of the established bulk-crystal physics and chemistry. III-V device interfaces often have an amorphous structure and extend over several atomic layers, instead of having a monocrystalline and atomically sharp structure. Reasons for that are discussed in this presentation.Therefore, it is not surprising that the III-V interfaces are a weak part of many practical devices (e.g. laser diode, infrared photodiode, micro-LED, HEMT) causing degradation in the current as well as future III-V applications. III-V interfaces include a high density of point defects, as compared to the uniform bulk crystals areas, which cause the electronic defect levels around the band gap at the interfaces, which further cause the electrical and optical losses. Use of III-V crystals is expected to increase in the areas like LED lighting, infrared optoelectronics, and high-speed transistor circuits, where it is not possible to utilize the Si crystals.Thus it is relevant to investigate and develop the III-V interface properties. The surface or interface passivation means a decrease in the defect-level density or/and in the effects of defect levels. It can be expected that the III-V passivation development requires a multistep procedure combining benefits of the different methods.Some commonly used passivation methods (e.g. wet chemistry, hydrogen forming gas, ALD self cleaning) are summarized in this talk. Our group has studied the issue whether it is useful to include ultrahigh-vacuum (UHV) treatments in a large arsenal of different passivation methods. The traditional surface science has been based on UHV technology. Our group has approached the III-V passivation challenge from a surface-science viewpoint. We have investigated in particular the clean surface properties and the surface oxidation in UHV conditions. Our group has addressed the question whether it is beneficial to pre-oxidize III-V surfaces intentionally because it is very difficult to avoid oxidation of III-V device surfaces. Our results support the previous findings that proper oxidation of III-V interfaces is a potential method to improve the devices performance.We have taken a step toward combining the surface science with the electrical characterization of III-V interfaces to find interconnections between electrical properties and surface-science ones. The high-resolution synchrotron x-ray photoelectron spectroscopy (XPS) has been used. Because XPS is a widely used method, we have addressed specific challenges in XPS analysis and that how the XPS analysis can be developed by including theoretical ab initio calculations. In this talk, it is also attempted to make a comparison to the silicon interface passivation.