Improved Passivation of a-Si:H / c-Si Interfaces Through Film Restructuring
- PDF / 1,838,306 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 82 Downloads / 125 Views
1066-A02-05
Improved Passivation of a-Si:H / c-Si Interfaces Through Film Restructuring M. Z. Burrows1,2, U. K. Das1, S. Bowden1, S. S. Hegedus1, R. L. Opila2, and R. W. Birkmire1 1 Insititue of Energy Conversion, University of Delaware, 451 Wyoming Rd., Newark, DE, 19713 2 Materials Science and Engineering, University of Delaware, 201 Dupont Hall, Newark, DE, 19716 ABSTRACT The as-deposited passivation quality of amorphous silicon films on crystalline silicon surfaces is dependent on deposition conditions and resulting hydrogen bonding structure. However the initial surface passivation can be significantly improved by low temperature postdeposition anneal. For example an improvement in effective lifetime from 780 µsec as-deposited to 2080 µsec post-anneal is reported in the present work. This work probes the hydrogen bonding environment using monolayer resolution Brewster angle transmission Fourier transform infrared spectroscopy of 100 Å thick films. It is found that there is significant restructuring at the a-Si:H / c-Si interface upon annealing and a gain of mono-hydride bonding at the c-Si surface is detected. Calculations show an additional 3.56 – 4.50 × 1014 cm-2 mono-hydride bonding at c-Si surface due to annealing. The estimation of the surface hydride oscillator strength in transmission mode is reported for the first time to be 7.2 × 10-18 cm on Si (100) surface and 7.5 × 10-18 cm on Si (111). INTRODUCTION Silicon heterojunction technology continues to be a topic of research interest due to continual advances in device performance and understanding. A key feature in maximizing silicon wafer based photovoltaic conversion efficiency is the minimization of saturation current. An excellent example of this application is the heterojunction-with-intrinsic-thin-layer cell design [1]. This report focuses on minimizing the saturation current through the passivation of crystalline silicon (c-Si) surface with hydrogenated intrinsic amorphous silicon ((i) a-Si:H). Specifically the aim is to display the relative insensitivity of minority carrier lifetime to bulk (i) a-Si:H film material properties and highlight the importance of the (i) a-Si:H / c-Si interface. The bulk and interface hydrogen bonding environment are studied predominantly by Fourier transform infrared absorption spectroscopy (FTIR). Short, low temperature anneals have been performed causing a large improvement in effective lifetime assuming an epitaxial growth regime is avoided. The change in the hydrogen bonding structure as a result of this anneal has been characterized and leads to an improved understanding of the importance of the hydrogen bonding structure at the c-Si interface. EXPERIMENT The experiment consists of two (n) c-Si substrate orientations, 30 Ω cm Si (111) and 1.5 Ω cm Si (100). DC plasma enhanced chemical vapor deposition is used for deposition of the a-
Si:H films. A simple yet rigorous substrate cleaning and H-termination procedure was applied independent of substrate orientation. The main steps include ultrasonic detergent clean,
Data Loading...
