Effects of nitrogen deficiency on electronic properties of AlGaN surfaces subjected to thermal and plasma processes

Abstract

Effects of device processing on chemical and electronic properties of AlGaN surfaces were investigated. The X-ray photoelectron spectroscopy analysis showed serious deterioration such as stoichiometry disorder and nitrogen deficiency (N deficiency) at the AlGaN surfaces processed by high-temperature annealing, H 2 -plasma cleaning, dry etching in CH 4 /H 2 /Ar plasma and deposition of SiO 2 . This resulted in high density of surface states at the processed AlGaN surface. Furthermore, the N deficiency introduced a localized deep donor level related to N vacancy (V N ) at AlGaN surfaces. Such electronic states governed by a V N -related deep donor and surface state continuum can cause strong Fermi level pinning at the AlGaN surface, reduction of the barrier height and excess leakage currents at the AlGaN Schottky interface and serious drain current collapse in AlGaN/GaN heterostructure field effect transistors. The SiN x -or Al 2 O 3 -based passivation scheme with a combination of a remote N 2 -plasma treatment was found to be effective in suppressing formation of V N -related surface defects at AlGaN surfaces. a)

High-Voltage AlGaN/GaN High-Electron-Mobility Transistors Using Thermal Oxidation for NiOxPassivation

“…A mixed layer, in which GaN, Ga, Al, Ni, and O coexisted, indicates that group-III oxides possibly formed as well. Group-III oxides such as GaO x and AlO x may leave group-III (Ga or Al) vacancies [15] as deep states. The reaction process of Ni and O in the AlGaN barrier may be related to the formation of deep states.…”

Control of Buffer-Induced Current Collapse in AlGaN/GaN HEMTs Using SiNx Deposition

“…These ions would be attracted to negatively charged threading dislocations due to their trapping of electrons [27], this could change their electrical conductivity and hence the vertical conductivity in the surface epitaxy. An alternative picture would be diffusion of nitrogen out of the epitaxy, it has been shown that nitrogen can diffuse from the surface leaving vacancies which increase leakage [28]. Future work should investigate the mechanism for this observed increase in vertical conductivity in these devices .…”

Improvements of electronic and optical characteristics of n-GaN-based structures by photoelectrochemical oxidation in glycol solution

“…A GaN layer after growth naturally contains many defects near the surface. 3,9,44 These defects tend to generate electronic surface levels that capture carriers, resulting in nonradiative recombination and degradation of the light emitting efficiency. Through oxidation, these defects could have been consumed into the oxide layer: namely, defects near the surface could be reduced by oxidation.…”

“…In dry etching, for example, these high energies are usually supplied by accelerated ions or plasma-assisted species. Dry processes, however, use highenergy reactions with plasma or high-temperature conditions and thus tend to generate surface damage and defects ͑V N ͒, 8,9 leading to high-density surface states, formation of shallow donor levels, 10,11 and large leakage currents. 9,12 These surface electronic states can capture carriers, causing to unintentional surface charge up, nonradiative recombination, and Fermi-level pinning, thus affecting device characteristics.…”