XPS study of Au/GaN and Pt/GaN contacts

Abstract

Au/GaN and Pt/GaN contacts have been studied with XPS. According to XPS depth profiling, the N signal is weak in the region below the metal contact and the Pt or Au signal decreases much more slowly than expected for a sharp interface. Next, we have performed in situ studies of the formation of Au contacts on GaN. In contrast to the results from depth profiling, we observe 2D growth and little or no chemical interaction between Au and GaN. This suggests that conventional calculations of sputtering yields and ion-beam-induced mixing cannot be applied to the analysis of noble metal/GaN depth profiles. Heating during or after Au deposition results in strong clustering, observed by both XPS and AFM. The Schottky barrier height measured by XPS is 1.15 eV.

X-ray photoemission determination of the Schottky barrier height of metal contacts to n–GaN and p–GaN

“…Island formation was observed via AFM for Pd, Au, and Al grown at room temperature. 38,39 The surface-barrier height values determined in this study are similar to values found in the literature for related systems ͑Table II͒. When possible, these values are reported in the table for the specific combination of sample doping, chemical pretreatment, metal, and surface-barrier height measurement technique, closest to those used here.…”

“…The other five metals could possibly be forming islands, but they are not observed as illustrated for Ni on n-GaN. Although there have been reports of layer-by-layer growth in the literature for Pd, 34 Pt, 37 and Au, 38 there has also been evidence for island formation. Island formation was observed via AFM for Pd, Au, and Al grown at room temperature.…”

Schottky barrier formation at the Au to rare earth doped GaN thin film interface

“…Although layer-by-layer growth for Au on GaN has been reported [18], there has also been evidence of island formation [18,23,56]. Here, we find compelling evidence that thin layers of gold do not wet and cover the GaN surface, even with rare earth doping of the GaN.…”

“…Surface alloying can occur [14] and a large range of experimentally measured Schottky barrier heights has been reported (0.76-1.40 eV) at the Au to n-type GaN interface [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], using photoemission spectroscopy (PES), current-voltage (I-V) and capacitance voltage (C-V) characteristics, and internal photoemission [30]. However, the generally accepted value is about 1.08 eV [31].…”

“…With this is mind, we have engaged in investigations of the interface properties of RE x Ga 1−x N (RE = Yb, Er, Gd) semiconductors with Au metal overlayer deposition under UHV conditions. Our studies of the Au to RE x Ga 1−x N semiconductor interface properties were performed much in the manner of other studies of the Au to GaN interface [18,[20][21][22][23].…”