On the link between electroluminescence, gate current leakage, and surface defects in AlGaN/GaN high electron mobility transistors upon off-state stress

Abstract

The degradation of AlGaN/GaN high electron mobility transistors after off-state stress is studied by means of electroluminescence (EL) analysis, gate leakage current (Ig) monitoring, and atomic force microscopy (AFM) mapping of the semiconductor surface. It is found that the degradation of Ig upon stress is due to the combined effect of the individual defects underlying each of the EL spots, which contribute a few μA each to the total Ig. After removal of contacts and passivation, a direct one-to-one correspondence between EL spots and pits on the semiconductor surface is found. Reverse bias, conducting-tip AFM imaging showed that these surface pits do indeed act as leakage paths. Thus, the direct relationship between EL hot spots, surface pits, and gate current leakage is demonstrated. Discussion on the morphology of the surface pits and their possible origin is also provided.

Electrical and structural degradation of GaN high electron mobility transistors under high-power and high-temperature Direct Current stress

“…[1][2][3][4][5][6][7][8][9] Several mechanisms have been postulated to explain the various degradation patterns that have been observed. [8][9][10][11][12][13][14][15][16][17][18] Several studies [19][20][21][22][23][24][25] have shown the appearance of prominent physical damage (dimples, grooves, pits, trenches, and cracks) on the semiconductor surface under the edge of the gate after prolonged OFF-state stress. The damage extends through the GaN cap and the AlGaN barrier layer and in some extreme cases reaches into the GaN buffer layer.…”

Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors

“…These EL emission points are associated with the formation of highly localized current leakage pathways, electrically shorting the gate to the 2DEG through the AlGaN barrier. 8,17 These emission regions are expected to be much smaller than the EL emission wavelength and are confined to the 2DEG at the AlGaN/GaN interface. Off state EL emission is therefore optimal for evaluating the lateral resolution of the SIL.…”

“…EL emission is observed at the drain edge of the gate in the standard microscope image, where the electric field is located. 8,9,17 However, identification of the exact location of the emission is lacking due to the finite spatial resolution, which is ~750 nm around the peak detected EL emission wavelength of 700-800 nm. Figure 5(b) shows the SIL-enhanced EL image, individual EL emission spots are clearly resolved and can be unambiguously located, exactly at the gate edge where the peak electric field is predicted.…”

“…[ 3,4,6,11,15 ] and Refs. [ 7,9,17 ], respectively. All measurements were performed at an ambient temperature of 22°C.…”

“…Previously reported micro-Raman thermography or electroluminescence microscopy measurements have been performed using an objective lens with an NA~0.5, enabling sufficient working distances of >5mm. [3][4][5][6][8][9][10][11][14][15][16][17] The optical resolution provided by an 0.5 NA objective lens is therefore used as a benchmark in this paper.…”