Comment on “Low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni∕Au films” [J. Appl. Phys. 86, 4491 (1999)]

Abstract

A very low barrier height (∼0.055V) at the p-GaN side in energy band diagram of p-NiO∕p-GaN interface was obtained in the paper: “low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni∕Au films.” They contributed the low contact resistance to the low energy barrier height for holes. We indicate the mistake of their calculation and obtain a barrier height of 2.28V and a notch of 0.19V on the p-GaN side and the p-NiO side, respectively, in this comment.

Fabrication and Electrical Properties of Grain-Oriented 0.91Pb(Zn_1/3Nb_2/3)O₃– 0.09PbTiO₃ Ceramics

“…Since the thickness of the testing sample was approximately 0.67mm, the coercive electric field E c was calculated to be 8.9 kV/cm, according to the formula as follows: E c = V c /d; where V c is the reversal voltage, which can be obtained from the hysteresis loop. The Pr and Ps values of the as-grown PZN-PT crystals are nearly equal to those reported by Yu et al [7], but the E c values are 3.5 kV/cm higher than that of PZN-PT crystals, which was characterized by those authors. This may be ascribed to the following factors: (1) the sample was not poled under relatively high temperature Optoelectronic Materials before ferroelectric characterizations performed; (2) the quality of the characterized sample was inferior due to the defects induced by the fluctuation of growth parameters.…”

Origins of the Schottky Barrier to a 2DHG in a Au/Ni/GaN/AlGaN/GaN Heterostructure

“…These defects might be assigned to the Ga vacancy that acts as acceptor (a result of removing native GaO x on the GaN), with an energy level of 0.1–0.3 eV and 0.15 eV from the valence band maximum. This behavior is far from ideal thermionic field-emission theory used previously to extract the SBH to p-GaN, ,,, which assumes a single SB fitted to the entire range of temperature, from a plot of resistivity versus temperature, which is clearly not the case when n ≠ 1. Okumura reports three ranges of behavior for their contacts based on (i) N A – N D < 2e19/cm 3 , resulting in the onset of Schottky behavior, (ii) Ohmic behavior between 3E19–7E19/cm 3 attributed to hole tunneling via field emission, whereas (iii) higher doping concentrations show a peculiar increase in resistivity due to deactivation of Mg but without any accompanying Schottky behavior in their I – V .…”

NiO gate GaN-based enhancement-mode hetrojunction field-effect transistor with extremely low on-resistance using metal organic chemical vapor deposition regrown Ge-doped layer

“…Figure 1 shows a schematic cross section of a GaN HFETs with a p-type material for the gate and a band diagram of various gate materials. [14][15][16] The p-type NiO is a gate material suitable for realizing normally-off operation in GaN HFETs because this material has a wide bandgap of 4 eV and its equivalent work function is as high as those of p-GaN and p-AlGaN, which enable normally-off operation. 11,12) In this lateral device, R on can be effectively reduced by reducing the distance between S=D electrodes.…”