Nitride Based Schottky-Barrier Photovoltaic Devices
- PDF / 311,970 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 48 Downloads / 204 Views
1040-Q09-27
NITRIDE BASED SCHOTTKY-BARRIER PHOTOVOLTAIC DEVICES Balakrishnam R Jampana1, Omkar K Jani2,3, Hongbo Yu2, Ian T Ferguson2, Brian E McCandless4, Steven S Hegedus4, Robert L Opila1, and Christiana B Honsberg3 1 Materials Science and Engineering, University of Delaware, 201 Dupont Hall, Newark, DE, 19716 2 School of Electrical and Computer Engineering, Georgia Institute of Technology, 266 Ferst Dr NW, BH 195, Atlanta, GA, 30332 3 Electrical and Computer Engineering, University of Delaware, 201 Evans Hall, Newark, DE, 19716 4 Institute of Energy Conversion, University of Delaware, 451 Wyoming Road, Newark, DE, 19716 ABSTRACT Schottky-barrier photovoltaic devices are fabricated by selective metal deposition on pGaN. A 1.25 V open-circuit voltage is observed for the best device. Devices were optimized by annealing in forming gas at temperatures ranging from 550oC to 700oC. Annealing time and forming gas flow rate are used to control the metal-semiconductor Schottky barrier formation. Optimum fabrication parameters are achieved based on photovoltaic response from the devices under UV illumination. Barrier heights (0.47 eV - 0.49 eV) were used as basis to compare the device response. The Schottky-barrier height is very sensitive to processing conditions, for example a 2.5% increase in barrier height is observed when Schottky contact annealing temperature is changed from 600 oC to 650 oC. Under UV illumination, the open-circuit voltage and short-circuit current increase with increasing annealing temperature while the series resistance decreases under such conditions. INTRODUCTION In recent years, the potential of InxGa1-xN has been investigated for applications in solar energy conversion [1]. The bandgap of InxGa1-xN can be tuned between 0.69 eV and 3.4 eV by varying the indium to gallium ratio in the alloy. A technological challenge in forming a p-n junction by MOCVD is p-type doping of InxGa1-xN, particularly at lower bandgaps due to high ntype background concentration [2]. Alternatively, a depletion region can by formed by Schottkybarrier devices for use as solar cells. Silicon Schottky-barrier solar cells have been demonstrated in the past [3], [4]. The present work shows a similar approach to develop Schottky-barrier solar cell from III-nitride semiconductors. The fabrication of such devices does not involve any form of plasma ion etching and, hence, the devices are less prone to associated damage. Therefore, such structures are ideal of assessing the potential for new photovoltaic materials like InxGa1-xN grown by MOCVD, MBE or bio-inspired growth. Schottky-barriers are formed at metal-semiconductor or metal-insulator-semiconductor interfaces, where the barrier height depends on the difference between the metal work function and semiconductor Fermi level. This paper addresses the fabrication of Schottky-barrier photovoltaic device on p-GaN, which is the first step towards similar InxGa1-xN devices. Mori and Kozawa [5] have studied the Schottky barrier formation and contact resistance of as-
deposited met
Data Loading...
