Utilizing Polarization Induced Band Bending for InGaN Solar Cell Design
- PDF / 685,925 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 214 Views
1167-O01-04
Utilizing Polarization Induced Band Bending for InGaN Solar Cell Design Balakrishnam R Jampana1, Ian T Ferguson2, Robert L Opila1, Christiana B Honsberg3 1 Material Science and Engineering, University of Delaware, Newark, Delaware 19716, USA 2 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA 3 Electrical Engineering, Arizona State University, Tempe, Arizona 85287, USA ABSTRACT Strong polarization effects observed in III-nitride materials can invert the surface carrier type. The corresponding band bending can be used to design InGaN solar cells. Similar surface inversion was observed in the past with silicon-based Schottky-barrier solar cells, but was limited by Fermi level pinning. The formation of two-dimensional electron gas by polarization fields in III-nitrides has been reported. Using a similar idea, the growth of a thin AlN capping layer on p-InGaN has resulted in band bending, hence depletion region, under the surface that can be used to separate any generated photo-carriers. Hall measurements at different depths on these structures confirm the inversion of surface carrier type. Solar cells based on this concept have resulted in an open circuit voltage of 2.15 V and short circuit current of 21.8 µA. INTRODUCTION Schottky-barrier solar cells invert the surface type of the semiconductors and are formed by metal deposition on semiconductors. The Schottky barrier height depends on the difference between metal work function and the semiconductor Fermi level. Silicon-based Schottky solar cells have been studied in the past [1]. The main limitation of these devices was Fermi level pinning to mid-band gap, limiting the open circuit voltage to half the band gap. Photo-response from III-nitrides Schottky devices were studied on GaN using several metal contacts. InGaN based Schottky devices have not yet been reported. Alternate approaches to invert the surface in other semiconductors have not been possible, but in III-nitride materials there is the inherent polarization which can be used to invert surfaces. InGaN materials with their wide band gap range (0.7 to 3.4 eV) are ideal for solar cells to span most of the solar spectrum [2]. InGaN-based solar cells using quantum wells and p-i-n structures have been reported [3, 4]. A unique property of the III-nitrides is their inherent polarization property [5]. Strong polarization fields with formation of two-dimensional electron gas (2DEG) have been reported in III-nitrides and are used in high-electron mobility transistors [6]. The photo-response from surface inversion caused by the polarization property has not been explored in the past. In this paper a study of surface inversion caused by thin AlN on InGaN is presented. The theoretically calculated band diagrams are presented followed by experimental evidence showing the formation of 2DEG and finally the photo-voltaic response from a p-InGaN/AlN structure. The III-nitride solar cells formed by polarization are not formed by inversion from a Schottky m
Data Loading...
