Poly-crystalline Ge thin films prepared by RF sputtering method for thermo photo voltaic application
- PDF / 304,857 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 23 Downloads / 197 Views
A6.5.1
Poly-crystalline Ge thin films prepared by RF sputtering method for thermo photo voltaic application Daisuke Hoshi, Isao Nakamura and Masao Isomura Department of Electric & Electronic Engineering, Tokai University 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan ABSTRACT The poly crystalline Ge films were prepared by the RF sputtering method with Ar and Ar-H2 mixture gases. The crystallization temperature increases from 400 ˚C to 500 ˚C due to the H2 introduction into the sputtering gases. On the other hand, the H2 introduction decreases the absorption coefficients in the long wavelength region corresponding to lower energy values than the energy gap of Ge, although much higher absorption coefficients are observed in the case of the Ar sputtering. Probably, the gap state density decreases due to the hydrogen termination of dangling-bonds in the grain-boundaries. The (220) preferential orientation is stressed and the highest Hall mobility is obtained with 75% of the gas flow ratio [Ar/ (Ar+H2)]. The preferential growth probably causes higher quality Ge films. INTRODUCTION The use of waste heat is one of the most effective ways to solve the energy and environment issues. The waste heat comes from the solar radiation, geothermal heat, human’s activities and so on. Recently, the study of thermophotovoltaic (TPV) application has been paid attention as a new energy source [1]. This system is composed of a photon emitter, a spectral selective filter and a photovoltaic cell (PV-cell). The photon emitter radiates infrared light by receiving the energy from the heat source. In the spectral selective filter, infrared light is selected for the PV-cell. Then, the PV-cell converts the infrared light in electric power. The PV-cell for the TPV application is required to have a narrow energy gap which has enough sensitivity for infrared light. Conventionally, InGaAs and GaSb have been studied for the PV-cells [2] [3]. However, these are costly materials and have difficulties to produce large area cells because these are usually produced by Metal Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE) methods. In this report, we proposed poly-crystalline Ge films as materials for the PV-cells, because Ge has a sufficiently narrow energy gap and a low cost material compared with InGaAs or GaSb. Besides, the poly crystalline Ge films can be prepared by the RF sputtering method that enables relatively low cost and large area processes. EXPERIMENTAL DETAILS The poly crystalline Ge films were prepared on corning #7059 substrates by the RF sputtering method with Ar and H2 gas mixture. The gas flow ratios, Ar/ (Ar+H2), were varied from 37.5 to 100%, and the substrate temperatures were varied from 300 to 600 ˚C. The chamber pressure was 1.0 Pa, and the film thickness was set at 300 nm.
A6.5.2
The crystallinity was evaluated by the Raman spectroscopy and the XRD. The Raman spectroscopy was measured with He-Ne laser light (632 nm), whose intensity was 14 mW to prevent the crystallization of samples. The XRD ev
Data Loading...
