Dependence of Schottky barrier height on electronic and chemical properties of Ni/AlGaN contacts

Schottky contacts to AlGaN are of great importance to its applications in micro- and optoelectronic devices. To characterize the dependence of interfacial properties on Schottky barrier formation in this material system we have used low energy cathodoluminescence spectroscopy (CLS), secondary ion mass spectrometry (SIMS), internal photoemission spectroscopy (IPE), and I-V measurements to correlate the local chemistry of the Ni/AlGaN interfaces with the CLS electronic properties and the IPE/I-V electrical properties as a function of thermal, wet, and UV-ozone processing conditions. Ni/Al_0.32Ga_0.68N contacts has showed that diodes processed by UV-ozone cleaning with a buffered HF dip removes the resulting oxide and exhibits Schottky barrier heights (1.5-1.53 eV) greater than those for diodes processed by UV-ozone only or buffered HF only (1.36-1.44 eV). Annealing the diodes at 325°C and 425°C in ultra-high vacuum increases the Schottky barrier height in the order of 0.1 eV-0.25 eV to values greater than or equal to the barrier heights measured on the UV-ozone+buffered HF processed diodes. Similar increase with annealing in the Ni/AlGaN Schottky barrier height as measured by C-V have also been reported. The obtained results highlights the key role of initial surface chemistry and thermal annealing on the Ni Schottky barrier height in the AlGaN material system.