Defects in hydrogenated amorphous silicon carbide alloys using electron spin resonance and photothermal deflection spect
- PDF / 206,239 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 218 Views
1153-A18-05
Defects in hydrogenated amorphous silicon carbide alloys using electron spin resonance and photothermal deflection spectroscopy Brian J. Simonds,1 Feng Zhu2, Josh Gallon1,2, Jian Hu2, Arun Madan2, P. Craig Taylor1 1 Physics Department, Colorado School of Mines, Golden, CO 80401, U.S.A. 2 MV Systems, Inc., Golden, CO 80401, U.S.A. ABSTRACT Hydrogenated amorphous silicon carbide alloys are being investigated as a possible top photoelectrode in photoelectrochemical cells used for hydrogen production through water splitting. In order to be used as such, it is important that the effects of carbon concentration on bonding, and thus on the electronic and optical properties, is well understood. Electron spin resonance experiments were performed under varying experimental conditions to study the defect concentrations. The dominant defects are silicon dangling bonds. At room temperature, the spin densities varied between 1016 and 1018 spins/cm3 depending on the carbon concentration. Photothermal deflection spectroscopy, which is an extremely sensitive measurement of low levels of absorption in thin films, was performed to investigate the slope of the Urbach tail. These slopes are 78 meV for films containing the lowest carbon concentration and 98 meV for those containing the highest carbon concentration. INTRODUCTION Amorphous silicon carbide (a-SiC:H) has long been studied as a promising material for use in solar cells as a result of its tunable bandgap. Recently, interest has been extended to include use as a photoelectrode in photoelectrochemical cells for hydrogen production by splitting water [1-4]. For amorphous silicon (a-Si:H), several generally held principles have been developed relating film properties and eventual device performance made from such films. However, in the case of a-SiC:H, relationships between basic material characterization techniques and device performance have not been made explicit. In order to do this, we must first identify the parameters in the films we wish to eventually use as absorber layers in a pin solar cell. In this work, we investigate the opto-electronic properties of the films with photothermal deflection spectroscopy (PDS) and electron spin resonance (ESR). PDS will allow us to measure sub-bandgap absorption as well as give us an indication of the density of states from disorder and defect levels. ESR measurements will allow us to ascertain bonding structure resulting from the incorporation of carbon. EXPERIMENT A series of a-SiC:H films were made at MVSystems in Golden, CO by plasma enhanced chemical vapor deposition (PECVD) in a mixture of SiH4, CH4, and H2. The amount of carbon was controlled by varying the amount of methane in the gas mixture with methane gas ratios
[CH4/(SiH4 + CH4)] varying from 0.20 to 0.55. The bandgap, conductivity, and the parameter gamma (γ) were tested on Corning glass (type 1737) substrate. Gamma (γ) is related to the photoconductivity by σph=σ0Fγ where σ0 is a constant of proportionality and F is the intensity of the illumination [8]. Ou
Data Loading...
