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

Abstract

Synchrotron radiation-based x-ray photoemission spectroscopy was used to study the surface Fermi level position within the band gap for thin metal overlayers of Au, Al, Ni, Ti, Pt, and Pd on n-GaN and p-GaN. Nonequilibrium effects were taken into account by measuring the Fermi edge of the metal overlayer. There are two different behaviors observed for the six metals studied. For Au, Ti, and Pt, the surface Fermi level lies about 0.5-eV higher in the gap for n-type than for p-type GaN. For Ni, Al, and Pd, the surface Fermi level position is independent of doping, but varies from one metal to the other. Results for Ni, Pd, and Al fit a modified Schottky-Mott theory, while Au, Ti, and Pt demonstrate a more complex behavior. Atomic force microscopy was used along with photoemission to investigate the growth mode of each metal on the GaN surface.

Pd/GaN(0001) interface properties

“…The barrier height at the phase boundary of Pd/GaN, as calculated basing on the above data, amounts to 1.6 eV. This value is consistent with the literature results [4][5][6].…”

“…It is known as one of the candidates for the Schottky diodes on the n-type GaN substrate. The barrier height of those contacts ranges from 0.96 to 1.9 eV [4][5][6]. In this paper we report the results of our XPS, UPS, STM and LEED studies on the morphology of an interface and thin films of Pd on GaN(0001).…”

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

“…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].…”

“…The 1998 review of metal-GaN contact technology by Liu and Lau [19] reported that, for a variety of contact metals with both low and high work functions, Schottky barrier heights at the metal-GaN interface varied with metal work function, within the experimental scatter. Subsequent work by Rickert et al [23] supported a modified Schottky-Mott model at the metal-GaN interface for Ni, Pd, and Al, yet more 'complex' behavior when Au, Ti, and Pt were used as the contact metals. Additional experiments by Barinov et al [21,22] reported Schottky barrier heights at the Au-GaN interface that exceeded both work function difference (Schottky-Mott) and electronegativity difference (metal induced gap states) models.…”

X-ray photoemission spectroscopic investigation of surface treatments, metal deposition, and electron accumulation on InN

“…The photoemission technique required for this analysis has been previously used for a variety of metals on GaN. 14,15 InN samples were grown via migration-enhanced epitaxy during molecular beam epitaxy. 16 The sheet carrier concentration was between 9.30ϫ10 13 and 1.95ϫ10 15 cm Ϫ2 and the thickness was between 0.1 and 1.0 m for a given sample.…”