Electronic transport of polarization-induced, two-dimensional electron gases with extremely high sheet carrier density for ScAlN/GaN-based power devices (ScNius)

点击翻译按钮获取中文摘要

The joint project ScNius is being applied for within the DFG priority program "Energy Efficient Power Electronics". Its aim is to investigate the electronic transport properties of polarization-induced two-dimensional electron gases (2DEG) with extremely high interface charge densities (> 1013 cm-2), which are confined at the interface of ScAlN/GaN heterostructures. Based on the knowledge of the dominant scattering mechanisms for the 2DEGs creating the power transistor channel, the epitaxy and design of the ScAlN/GaN heterostructures will be optimized with respect to minimizing the sheet resistance of the processed "High Electron Mobility Transistors" (HEMTs). Based on this, power electronic devices with a significantly increased current-carrying capacity and energy efficiency compared to conventional GaAlN/GaN HEMTs are processed and demonstrated.In six work packages, systematically building upon each other, the epitaxy, analytics, technology, metrology, and simulation of ScAlN/GaN heterostructures and power devices will be performed. This procedure is supported by extensive theoretical and experimental preliminary work of the applicants in the research and development of GaN-based power electronic devices and the determination of all relevant material coefficients of hexagonal ScxAl1-xN layers (0 ≤ x ≤ 0.45). With the help of metal organic chemical vapor deposition (MOCVD), high quality ScAlN/GaN heterostructures are deposited and analyzed with respect to their structural properties. The obtained material structures allow enormously large polarization gradients at the ScAlN/GaN interface, which will allow 2DEGs with electron densities as high as 2·1013 to 6·1013 cm-2 and sheet resistances of less than 200 /sq. However, previous work shows that an increase in electron density decreases the mobility of the charge carriers. For this reason, the work in the first part of the project focuses on clarifying the electrical transport properties and the dominant scattering mechanisms of 2DEGs. With the help of theoretical methods (Schrödinger-Poisson and Monte Carlo simulations) and the available electrical measurement techniques, physical properties relevant for power transistors such as mobility, drift and saturation velocity will be determined. Based on these, the influence of alloy and interface scattering as well as the influence of point defects (e.g. charged point defects) and line defects (e.g. dislocations) will be ascertained. The gained knowledge will then be used to optimize the material structures with respect to the highest possible interface charge density and drift velocity of the 2DEGs.