Influence of premetallization surface treatment on the formation of Schottky Au-nGaN contacts

Abstract

The influence of premetallization surface preparation on the structural, chemical, and electrical properties of Au-nGaN interfaces has been investigated by x-ray photoemission spectroscopy ͑XPS͒, current-voltage measurement (I-V) and cross-section transmission electron microscopy ͑TEM͒. XPS analysis showed that the three GaN substrate treatments investigated i.e., ex situ hydrofluoric acid etch, in situ anneal in ultrahigh-vacuum ͑UHV͒, and in situ Ga reflux cleaning in UHV result in surfaces increasingly free of oxygen contamination. XPS and TEM characterization of Au-nGaN formed after the three premetallization surface treatments show that HF etching and UHV annealing produce abrupt, well-defined interfaces. Conversely, GaN substrate cleaning in a Ga flux results in Au/GaN intermixing. I-V characterization of Au-nGaN contacts yields a Schottky barrier height of 1.25 eV with a very low-ideality factor and very good contact uniformity for the premetallization UHV anneal, while the Ga reflux cleaning results in a much lower barrier ͑0.85 eV͒, with poor ideality and uniformity. I-V and XPS results suggest a high density of acceptor states at the surface, which is further enhanced by UHV annealing. These results are discussed in the context of current models of Schottky barrier formation.

Surface Preparation and Deposited Gate Oxides for Gallium Nitride Based Metal Oxide Semiconductor Devices

“…Acidic treatments such as HF can reduce the surface O concentration [76]. Lee et al [77] report that UV/O 3 and wet chemical treatments based on HF and HCl are very effective in removing surface C and reducing the native oxide thickness on GaN but it further suggests that high vacuum in situ cleaning methods are needed to obtain an oxygen free air exposed GaN surface.…”

Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au∕GaN Schottky contacts

“…For Au/ GaN Schottky contacts, several groups have reported their results. 2,3,5 However, few studies have been reported to investigate the influence of deep level centers ͑which are closely associated with the yellow emission band͒ on the capacitance-voltage characteristics of metalGaN Schottky contacts. In this letter, we show experimentally that the deep level centers located at about 1.3 eV can lead to typical anomalous reverse-bias C-V characteristics of Au/ GaN Schottky diodes, particularly the low-frequency C-V characteristics.…”

“…These are not well understood and are thus being actively investigated. [2][3][4][5][6][7][8] Having a work function of ϳ5.1 eV, gold ͑Au͒ is one of the most used metals in the fabrication of metal-semiconductor Schottky and Ohmic contacts. For Au/ GaN Schottky contacts, several groups have reported their results.…”

Structural and electrical characteristics of Ag/Al0.2Ga0.8N and Ag/Al0.3Ga0.7N Schottky contacts: an XPS study

“…2 are, however, at variance with those previously reported for GaN and AlGaN surfaces. Maffeis et al [7] found that a 600 °C anneal of GaN HF-etched surfaces resulted in a 0.35 eV upward band bending. Other studies of surface preparation of GaN have also, in the main, resulted upward band bending [8,9].…”