Reduction in Gate Leakage Current of AlGaN/GaN HEMT by Rapid Thermal Oxidation
- PDF / 228,019 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 68 Downloads / 173 Views
Reduction in Gate Leakage Current of AlGaN/GaN HEMT by Rapid Thermal Oxidation Sreenidhi T1, A. Azizur Rahman2, Arnab Bhattacharya2, Amitava DasGupta1 and Nandita DasGupta1 1 Microelectronics and MEMS Laboratory, Dept. of Electrical Engg., IIT Madras, Chennai, India. 2 Condensed Matter Physics and Material Science, TIFR, Mumbai, India. ABSTRACT Rapid Thermal Oxidation (RTO) of AlGaN barrier has been employed to reduce the gate leakage current in AlGaN/GaN High Electron Mobility Transistors. Current Voltage (I – V) and Capacitance Voltage (C – V) characteristics of Schottky Barrier diodes and Metal Oxide Semiconductor diodes are compared. At room temperature, reduction in gate leakage current over an order of magnitude in reverse bias and four orders of magnitude in forward bias is achieved upon oxidation. While the gate current reduces upon RTO, gate capacitance does not change indicating gate control over the channel is not compromised. I – V and C – V characterization have been carried out at different temperatures to get more insight into the device operation. INTRODUCTION AlGaN/GaN High Electron Mobility Transistors (HEMTs) have been a topic of great research interest over the last two decades due to their attractive characteristics. The gate of these devices is generally a Schottky Barrier (SB) diode which regulates the Two Dimensional Electron Gas (2DEG) in the channel. The high-density polarization charge present at the interface results in a high electric field across the barrier of the device [1]. This high electric field in association with the high density dislocations typically present in these materials results in high gate leakage currents. Gate leakage current in AlGaN/GaN HEMTs is a matter of great concern and has been widely studied [1-4]. Poole – Frenkel (PF) emission is said to be the major component of gate leakage current in the reverse bias. Gate leakage current results in high standby power dissipation and also poses a threat to the device reliability. Metal Oxide Semiconductor structures with ALD Al2O3 on AlGaN/GaN have been proposed to combat the gate leakage current and for surface passivation [5]. Thermal oxidation of the barrier AlGaN has also been considered for gate dielectric and device isolation [6-9]. Large reduction in the leakage current has been reported for selective thermal oxidation isolation over mesa isolation [6]. MOS HEMTs with thermally grown oxide at 900 °C have been reported by Inoue et al. [8]. However, the effect of thermal oxidation on gate characteristics is not presented clearly. Also the oxidation process is such that a significant amount of barrier gets oxidized thereby causing 2DEG depletion. Further, annealing at 900 °C for longer time is reported to have reduced the 2DEG concentration, in spite of protecting the active region with SiO2 during annealing [9]. Thus, in this work, a lower oxidation temperature (800 °C) is chosen. The effect of oxidation on structural and electrical characteristics is presented. Temperature dependence of gate Current – Voltage (I –
Data Loading...
