Abstract
In this work, GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barrier grown by plasma-assisted molecular beam epitaxy are successfully fabricated. The lattice registration of single crystal (111) Al on (0001) GaN is investigated using both in-situ reflection high-energy electron diffraction patterns and ex-situ high-resolution x-ray diffractions, and it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current, when biased at -2 V, are observed in single crystal Al/GaN SBDs comparing to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements. In the appendix, the effects of three different kinds of surface treatment and oxide post-annealing process on the interface state density of n-type MOS capacitors are evaluated by the conductance method. Boiling H2SO4 treatment prior to depositing Al2O3 is the best way to reduce the interface state density (~1011 eV-1cm-3). Post annealing at 850oC for 30 seconds could result in negative shift of threshold voltage.