Temperature dependence of electrical characteristics of Pt/GaN Schottky diode fabricated by UHV e-beam evaporation
© Kumar et al.; licensee Springer. 2013
Received: 21 August 2013
Accepted: 9 November 2013
Published: 15 November 2013
Temperature-dependent electrical characterization of Pt/n-GaN Schottky barrier diodes prepared by ultra high vacuum evaporation has been done. Analysis has been made to determine the origin of the anomalous temperature dependence of the Schottky barrier height, the ideality factor, and the Richardson constant calculated from the I-V-T characteristics. Variable-temperature Hall effect measurements have been carried out to understand charge transport at low temperature. The modified activation energy plot from the barrier inhomogeneity model has given the value of 32.2 A/(cm2 K2) for the Richardson constant A** in the temperature range 200 to 380 K which is close to the known value of 26.4A/(cm2 K2) for n-type GaN.
GaN has been the subject of strategic research among all compound semiconductors and has been explored widely and rightly for its various characteristics, like direct wide band gap, high breakdown field, high saturation velocity, and chemical and radiation hardness . The combination of all these properties makes GaN a preferred material for optoelectronics and high-temperature and high-power RF applications. In applications like power rectifier and HEMT, a metal–semiconductor contact with high Schottky barrier height (SBH), high rectification efficiency, and low reverse leakage current is needed [1, 2]. Also, the quality of the metal–semiconductor interface is affected by the process steps and deposition vacuum since contamination and oxide layer growth at the interface may result in SBH reduction and high leakage current by inducing local nanoscopic patches of low barrier heights. Werner and Güttler reported that these local patches follow a Gaussian distribution of barrier height and locally control the device characteristics in different temperature regimes of operation . Studies by Tung revealed that this kind of inhomogeneous behavior is observed in all semiconductors and results in overall decreased barrier heights . The contamination level and oxide layer can be minimized by following fabrication steps in a clean room and depositing Schottky metals in ultra high vacuum (UHV). According to the Schottky-Mott model, the Schottky barrier height is dependent on the metal work function and electron affinity of semiconductor χ (GaN χ = 4.1 eV) [1, 5, 6]. Metals like Pt, Ni, Pd, and Au which have high work function than GaN make a better choice for gate contact. Pt has a high work function (5.65 eV) that makes it ideal for use as Schottky contacts on n-type GaN, and it is also resistant to oxidation and corrosion . There are only a few reports on Pt/GaN Schottky barrier diodes. The Schottky barrier height of Pt/n-GaN has been reported with a value between 0.89 and 1.27 eV [7–12]. In the present paper, we report an investigation on good-quality Pt/GaN Schottky barrier diodes deposited in ultra high vacuum condition. Temperature-dependent I-V characteristics have been measured and analyzed using the barrier inhomogeneity model proposed by Werner and Güttler .
Results and discussion
Calculated Schottky diode parameters for Pt/n-GaN Schottky diodes
Apparent SBH (eV)
Reverse leakage current (IR) atVR = -1 V
6 × 10-11
1 × 10-11
4 × 10-11
2 × 10-12
5 × 10-11
5 × 10-11
5 × 10-11
In conclusion, a detailed electrical analysis of the Pt/n-GaN Schottky contacts prepared by evaporation has been made to determine the origin of the anomalous temperature dependence of the SBH, the ideality factor, and the Richardson constant calculated from the I-V-T characteristics. The variable-temperature Hall experiments have given an insight into the origin of barrier inhomogeneity observed commonly in n-GaN-based Schottky barrier diodes. The temperature dependence of the experimental values of SBH of the Pt/n-GaN has been described by two Gaussian distributions in the temperature range of 100 to 340 K. The modified activation energy plot from the barrier inhomogeneity model has given the value of 32.2 A/(cm2 K2) for the Richardson constant A** in the temperature range 200 to 380 K which is close to the known value of 26.4 A/(cm2 K2) for n-type GaN.
Ashish Kumar would like to gratefully acknowledge the University Grant Commission (UGC) for providing research fellowship. We are thankful to Dr. Seema Vinayak from Solid State Physical Laboratory (SSPL), Delhi, India, for providing help in the experiments.
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