Near Infrared Detectors and Solar Cells Based on Microcrystalline Silicon Germanium
- PDF / 212,837 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 7 Downloads / 228 Views
Near Infrared Detectors and Solar Cells Based on Microcrystalline Silicon Germanium M. Krause, H. Stiebig, R. Carius, H. Wagner Forschungszentrum Jülich GmbH, IPV, 52425 Jülich, Germany, [email protected] ABSTRACT Microcrystalline silicon germanium alloys (µc-Si1-xGex:H) exhibit an enhanced optical absorption in the near infrared region with increasing germanium content. Therefore, the employment of this material as intrinsic absorber is a promising challenge for thin film technology in photovoltaics and sensorics. The influence of hydrogen dilution on the material and the performance of pin diodes prepared in a PECVD process with 10 % GeH4 in the gas phase is discussed. These results are compared with the characteristics of diodes prepared with higher germane content in the gas phase. With increasing germane content the solar cell parameters Voc and FF decrease and the deposition regime where good optoelectronic properties are observed is narrowed. INTRODUCTION For photovoltaics or sensor applications low bandgap materials with high absorption coefficient are desired. Since µc-SiGe:H shows a higher absorption coefficient in the spectral range up to 2 eV than µc-Si:H, µc-SiGe:H pin diodes prepared by PECVD are investigated [1, 2, 3]. In previous investigations we used Si2H6 and GeH4 as source gases which limited microcrystalline growth to alloys with a germanium content to less than 40 % due to the limited hydrogen flow [4]. Importantly, we found a negligable influence of hydrogen dilution on the germanium built-in coefficient. In this study µc-Si1-xGex:H films and devices with comparable and higher germanium content were prepared by PECVD using SiH4 and GeH4 diluted in H2 up to 1:200. For monosilane instead of disilane we found a shift of the transition region from amorphous to microcrystalline growth towards lower hydrogen dilution. Studies of µc-Si:H pin diodes have shown the important role of hydrogen dilution determining the structural properties of the material. The best µc-Si:H solar cells were prepared near the transition region between microcrystalline and amorphous growth [5]. Therefore, we have focussed our investigations on the influence of hydrogen dilution on the performance of µc-SiGe:Hdiodes. The diode characteristics in the dark and under illumination were investigated. EXPERIMENTAL DETAILS The µc-Si1-xGex:H films and solar cells were deposited by PECVD at ~ 200 °C substrate temperature, a plasma excitation frequency of 95.7 MHz, a pressure of 200 mTorr and a power of 30 W for a substrate size of 10 x 10 cm². The mixture of monosilane (SiH4) and germane (GeH4) was varied ([GeH4]/([SiH4]+[GeH4]) = 10 %, 20 %, 30 %), denoted as germane content. Concerning the composition in the solid phase a film prepared with a certain GeH4 content shows a germanium content about twice as much as in the gas phase. The dilution of the process gases in hydrogen γ = ([SiH4]+[GeH4])/[H2] was varied from 0.5 to 4.0 %. Deposition rates between 0.2 and A13.7.1
3.7 Å/s were achieved. The structural properties of the sa
Data Loading...
