Distribution of built‐in electric field in GaN(cap)/AlGaN/GaN(buffer) transistor heterostructures with various AlGaN thicknesses

Abstract

AbstractA theoretical approach supported by experimental data (i.e., measurements of built‐in electric field in AlGaN layer and two dimensional electron gas (2DEG) concentration at the AlGaN/GaN interface) has been proposed to determine the distribution of built‐in electric field in undoped polar GaN(cap)/AlGaN/GaN(buffer) heterostructures. In this method the Schrodinger and Poisson equations are solving self consistently for various boundary conditions. It is clearly shown that the built‐in electric field in AlGaN layer depends mainly on the surface boundary condition whereas the concentration of 2DEG at AlGaN/GaN interface depends on two boundary conditions (i.e., the Fermi‐level position on GaN(cap) surface and inside GaN(buffer) layer). Comparing the measured built‐in electric field in AlGaN layer with this one calculated for various Fermi‐level position on GaN surface it is possible to determine the Fermi‐level pinning on GaN(cap) surface. Next it is possible to determine the Fermi‐level position in GaN(buffer) layer at a given distance from AlGaN/GaN interface. For this purpose the measured 2DEG concentration was compared with this one calculated for the fixed Fermi‐level position on GaN(cap) surface and the varied Fermi‐level position in GaN buffer layer. In this way the distribution of built‐in electric can be determined for real heterostructures for which the built‐in electric field in AlGaN layer is measured by electromodulation spectroscopy and 2DEG concentration is extracted from Hall measurements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)