Depth-resolved spectroscopy of interface defects in AlGaN/GaN heterostructure field effect transistors device structures

Abstract

We report depth-resolved low energy electron excited nanometer spectroscopy from AlGaN/GaN heterostructure field effect transistors structures with AlGaN thicknesses as thin as 20 nm. By varying the voltage of a low energy electron beam in ultrahigh vacuum, we can determine whether defect induced luminescence is being emitted from the GaN buffer layer, the interfacial region where the two-dimensional electron gas (2DEG) resides, and the AlGaN barrier layer. By increasing the GaN buffer thickness, known to enhance the electron concentration of the 2DEG by reducing the dislocation density in the active region, we observed an enhancement in AlGaN luminescence, and a 20% reduction in the full width at half maximum of the near band edge peak. When a similar structure with no 2DEG is measured, we find a factor of 8 increase in midgap yellow luminescence relative to the GaN buffer emission. Taken together, these findings indicate that differences in buffer layer thickness and electrical quality can affect not only dislocation density and point defect densities, but also the optical properties of the AlGaN barrier layer and its 2DEG interface.