Barrier Inhomogeneity of Ni Schottky Contacts to Bulk GaN

Abstract

Gallium nitride (GaN) is a promising candidate for high‐power and high‐frequency devices. To date, the lack of large area bulk GaN materials of reasonable cost and quality has limited the technology almost completely to lateral devices. However, vertical structures are attractive to obtain a higher current density and a reduced device size. In this work, the electrical behavior of a Ni/Au Schottky barrier on bulk GaN material is studied, using vertical Schottky diodes. The forward current–voltage characteristics of the diodes reveal a temperature dependence of both the ideality factor (n) and of the Schottky barrier height (ΦB). The ideal value of the barrier of 1.72 eV extrapolated at n = 1 is in agreement with the results obtained by capacitance–voltage measurements. A nanoscale electrical analysis performed by conductive atomic force microscopy (C‐AFM) allow to visualize the barrier height inhomogeneity and to correlate the current distribution to the surface morphology of the material. The barrier inhomogeneity explains the temperature behavior of ideality factor and barrier height determined by the macroscopic diodes. Preliminary structural analyses carried out by transmission electron microscopy (TEM) of the metal semiconductor interface revealed a typically flat Au/Ni bilayer structure, the Ni layer being epitaxial to GaN, with some mosaicity.

Atomic Layer Deposition of ZnO for Modulation of Electrical Properties in n-GaN Schottky Contacts

“…33,34 Using C-V data, Greco et al obtained a barrier height of 1.72 eV for the Ni Schottky contact to bulk GaN. 35 The presence of residual contamination from processing was suggested as one possibility to explain the high barrier height obtained by C-V analysis. The higher value of q/ B CÀV compared with q/ B IÀV in Ni/n-TiO 2 /p-Si/Al heterojunction diodes is associated with nonuniformity in the interfacial layer and the distribution of interfacial charges at the metal-semiconductor interface.…”

400 °C Sensor Based on Ni/4H-SiC Schottky Diode for Reliable Temperature Monitoring in Industrial Environments

“…Forward low-bias behavior of ideal Schottky diodes is conventionally characterized by the thermionic emission (TE) equation, [6,7,8,9,10,11,12,13,31,32,33,34,35,36,37,38], ISD≅AnAST2exp(−ΦBn,normalTVth)exp(VSDnVth).…”

“…While, ideally, Φ Bn,T and n should be temperature-independent, value variation for these parameters has been ubiquitously observed for Schottky diodes [6,7,8,9,10,11,12,13,14,31,32,33,34,35,36,37,38]. This phenomenon is attributed to inhomogeneities present on the Schottky contact surface, which leads to spatial variations of the Schottky barrier height (SBH).…”

“…This phenomenon is attributed to inhomogeneities present on the Schottky contact surface, which leads to spatial variations of the Schottky barrier height (SBH). This topic was widely investigated, with many propositions of characterization methodologies [6,7,8,13,31,32,33,34,35,36,37,38]. One such recent development directed towards high-temperature (room to 450 °C) behavior modeling was proposed for Ni/SiC Schottky diodes [7,8,13].…”

Current transport in Ni Schottky barrier on GaN epilayer grown on free standing substrates

“…However, the absence of lattice parameter mismatch makes the GaN epilayer properties more dependent with the quality of the GaN substrate, which motivates the present study. In previous papers, the high leakage current in Schottky diodes on bulk GaN was correlated with the presence of structural defects in the epilayer [11,12,13]. Moreover, the mechanisms of current transport dominating the electrical behaviour at the metal/GaN interface have been recently discussed [14,15].…”