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 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 (R S ) are in the range of 636 at 90 K to 220 at 410 K using Cheung's method. Based on the above observations, the bo , n and R S values are seen to be strongly temperature dependent. The flat-band barrier height bf (T = 0 K) and temperature coefficient α were found to be 0.67 eV and 2.81 × 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.
Electrical and structural properties of palladium/molybdenum (Pd/Mo) Schottky contacts on n-type GaN have been investigated as a function of annealing temperature by current-voltage (I-V), capacitance-voltage (C-V), x-ray diffraction (XRD) and Auger electron spectroscopy (AES) techniques. An as-deposited Pd/Mo/n-GaN Schottky diode exhibits a barrier height of 0.68 eV (I-V) and 0.82 eV (C-V), which increased to 0.75 eV (I-V) and 0.89 eV (C-V) after annealing at 400 • C. However, it is noted that the barrier height slightly decreased to 0.73 eV (I-V) and 0.87 eV (C-V) when the contact was annealed at 500 • C. A maximum barrier height of 0.78 (I-V) and 1.09 eV (C-V) was achieved on the Pd/Mo contacts annealed at 600 • C. The Norde method was also employed to extract the barrier height of Pd/Mo contacts, and the values are 0.70 eV for the as-deposited and 0.82 eV for the contact annealed at 600 • C which are in good agreement with those obtained by the I-V technique. Based on the Auger electron spectroscopy and x-ray diffraction studies, the formation of gallide phases at the Pd/Mo/n-GaN interface could be the reason for the increase of Schottky barrier heights upon annealing at elevated temperatures. The AFM results showed that there was no significant degradation in the surface morphology (rms roughness of 4.61 nm) of the contact even after annealing at 600 • C. These results make Pd/Mo Schottky contacts attractive for high-temperature device applications.
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