Analysis of the current-voltage characteristics of the Pd/Au Schottky structure on n-type GaN in a wide temperature range

We report on the temperature-dependent electrical characteristics of the Au/Pd/ n-GaN Schottky diode in the temperature range of 90-410 K. The barrier heights and ideality factors of Schottky diodes were found in the range 0.23 eV and 3.5 at 90 K to 0.97 eV and 1.9 at 410 K, respectively. It was observed that the zero bias barrier height Phi(bo) decreases and the ideality factor n increases with a decrease in temperature. Such behavior is attributed to barrier inhomogeneities by assuming a Gaussian distribution of barrier heights at the interface. The estimated values of series resistance (RS) are in the range of 636 Omega at 90 K to 220 Omega at 410 K using Cheung's method. Based on the above observations, the Phi(bo), n and RS values are seen to be strongly temperature dependent. The flat-band barrier height Phi(bf) (T = 0 K) and temperature coefficient a were found to be 0.67 eV and 2.81 x 10(-3) eV K-1, respectively. Further, the homogeneous barrier height is estimated from the linear relationship between temperature-dependent experimental effective barrier heights and ideality factors and the value is approximately 1.31 eV. The effective Richardson constant is determined to be 20.43 A cm(-2) K-2 and is in good agreement with the theoretical value. It is concluded that the temperature-dependent I-V characteristics of the Au/Pd/ n-GaN Schottky diode can be successfully explained on the basis of thermionic emission (TE) mechanism with the Gaussian distribution of the barrier heights

Effects of thermal annealing on the electrical and structural properties of Pt/Mo Schottky contacts on n-type GaN

Thermal annealing temperature effects on the electrical and structural properties of platinum/molybdenum (Pt/Mo) Schottky contacts on n-type GaN have been investigated by current-voltage (I-V), capacitance-voltage (C-V), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. As-deposited Pt/Mo/n-GaN Schottky diode exhibits barrier height of 0.75 eV (I-V) and 0.82 eV (C-V). Upon annealing at 400 and 500 A degrees C, the barrier height slightly increased to 0.77 eV (I-V) and 0.92 eV (C-V) and 0.82 eV (I-V) and 0.97 eV (C-V), respectively. A maximum barrier height of 0.83 eV (I-V) and 0.99 eV (C-V) is obtained on the Pt/Mo contacts annealed at 600 A degrees C. X-ray photoelectron spectroscopy results shows that the Ga 2p core-level shift towards the low-energy side for the contact annealed at 600 A degrees C as compared to the as-deposited one. Based on the results of XPS and XRD studies, the formation of gallide phases at Pt/Mo/n-GaN interface could be the reason for the increase of Schottky barrier heights upon annealing at elevated temperatures. The atomic force microscopy (AFM) results showed that the Pt/Mo contact does not seriously suffer from thermal degradation during annealing even at 600 A degrees C (RMS roughness of 5.41 nm). These results make Pt/Mo Schottky contacts attractive for high temperature device applications