Temperature Diagnosis of Bulk GaN-based Schottky Diode by Raman Spectroscopy Hui Xu 1 , Siddharth Alur 1 , Yaqi Wang 1 , An-Jen Cheng 1 , Kilho Kang 1 , Claude Ahyi 1 , John Williams 1 , Minseo Park 1 *, Chaokang Gu 2 , Andrew Hanser 3 , Tanya Paskova 3 , Edward A. Preble 3 , Keith R. Evans 3 , and Yi Zhou 4 1 Department of Physics, Auburn University, Auburn, AL 36849 2 Department of Chemistry and Biochemistry, Auburn University, Auburn, AL, 36849 3 Kyma Technologies, Inc., 8829 Midway West Road, Raleigh, NC 27617 4 Department of Electrical Engineering, University of California, Los Angeles, CA 90095 *corresponding author Keywords: GaN, Schottky diode, Raman Abstract Intensive research has been focused on the GaN based electronic devices due to their intrinsic properties such as large band gap, high critical breakdown field and high electron saturation velocity, which provide great potential for high power and high frequency applications. Schottky diodes are useful components for high power electronics because of their fast switching. However, a significant limitation of device performance is the self-heating problem. Therefore, accurate determination of the device temperature is very important. In our experiment, we fabricated vertical Schottky rectifiers based on freestanding GaN substrate, where semi-transparent Ni was patterned on the Ga-face as the Schottky contact and full backside ohmic contact Ti/Al/Pt/Au was deposited on the N-face. Afterwards, Raman spectra were collected as a function of forward bias. The Raman E2 peak was found to shift and broaden systematically with device operating power. We conclude that micro-Raman spectroscopy is a great non-contact tool to monitor the thermal characteristics of electronic devices under operation. INTRODUCTION Since the operation of GaN-based light-emitting diode (LED) was demonstrated, nitride-based semiconductor has attracted scientific and commercial interests. For example, green nitride-based LEDs are widely applied in traffic signals. Due to their unique material properties, there are many promising applications for GaN, especially in high power and high frequency area. Thanks to recent technology, great improvement has been made to GaN based devices, although difficulties still exist. Self-heating is one of the issues. In the case of high electron mobility transistor (HEMT) at high bias, temperature increase due to self- heating can negatively affect the device performance [1]. Raman Spectroscopy is used by several groups for temperature measurement of HEMT [2, 3]. Schottky diodes are preferred in high power electronics, which also suffer from self-heating problem. However, no report has been published for temperature diagnosis of bulk GaN based Schottky diodes which are under operation. EXPERIMENT Our devices were fabricated based on the bulk GaN wafer with a thickness of 500 µm, and the wafer was produced at Kyma Technologies, Inc. The samples were initially immersed in acetone, TCE and methanol in an ultrasonic bath. Afterwards, they were treated with heated HCl solution to remove the native oxide. A 4-layered metal stack Ti/Al/Pt/Au was sputtered on the full backside (N-face GaN) of the wafer. Subsequently, the ohmic contact was annealed at 750 o C for 30s in the nitrogen atmosphere. Semi- transparent metal Ni was patterned on the front Ga side as circular Schottky contacts. Then, the current-voltage (I-V) and capacitance-voltage (C-V) curves were measured to characterize the Schottky diodes. From the C-V curve, the carrier concentration was determined to be ~3×10 16 cm -3 . The 441.6 nm line (80 mW) from HeCd laser was used to collect Raman spectra when the devices were heated through applied bias and hot plate. RESULTS AND DISCUSSION Figure 1 is the low field I-V curve with a forward voltage up to 2 V and figure 2 is the high field I-V curve with a forward voltage up to 20 V. The current in a Schottky rectifier is described through thermionic emission model by the following equation: CS MANTECH Conference, May 18th-21st, 2009, Tampa, Florida, USA