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TiAl Ohmic contact on GaN, in situ high or low doped or Si implanted, epitaxially grown on sapphire or silicon

2012; Wiley; Volume: 209; Issue: 6 Linguagem: Inglês

10.1002/pssa.201127564

1862-6319

F. Cayrel, O. Ménard, Arnaud Yvon, Nicolas Thierry‐Jebali, C. Brylinsky, Emmanuel Collard, Daniel Alquier,

Metal and Thin Film Mechanics

Abstract In this work, the Ti/Al Ohmic contact quality on n‐type gallium nitride (GaN) films has been studied as a function of different process parameters such as surface cleaning procedure, etching, thickness of the deposited layers or annealing conditions. GaN epilayers, with uniform doping concentration from 1 × 10 16 to 5.8 × 10 18 at./cm 3 were grown on sapphire or silicon substrates using AlN and/or AlGaN buffer layers. Electrical characterizations were made using circular transfer length method (cTLM) patterns with a four‐probe equipment. Specific contact resistance (SCR) was then extracted from current–voltage ( I – V ) characteristics, for all the process conditions. Contact structures depending on experiment parameters were studied by means of (scanning) transmission electronic microscopy (STEM‐TEM). Our results reveal that process parameters such as surface treatment have a lower impact than annealing temperature or metal thickness and annealing duration. Finally, SCR values of 1 × 10 −6 Ω cm 2 can be reproducibly achieved. Moreover, good Ohmic contacts have been obtained on etched surfaces or on low‐doped layers implanted with Si. This low value demonstrates a good Ohmic contact and this large parameter process window is of high interest for future device fabrication based on GaN (planar or mesa structures).