Techniques for measuring the composition of hydrogenated amorphous silicon–germanium alloys

Abstract

online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste to be published in J. Non-Cryst. Solids (ICAMS18) Key Words (JNCS index terms): A180, amorphous silicon-germanium (a-SiGe:H), Hot-Wire C185 (HWCVD), I160, S130, Electron Probe Micro Analysis (EPMA), Nuclear Reaction Analysis (NRA), R190, S180, G150 AbstractWe grow hydrogenated amorphous silicon-germanium alloys by the hot-wire chemical vapor deposition technique at deposition rates between 0.5 and 1.4 nanometers per second. We prepared a set of these alloys to determine the concentrations of the alloying elements as measured by various techniques. This set consists of samples throughout the range of germanium alloying from 0% (a-Si:H) to 100% (a-Ge:H). We find that by making the appropriate calibrations and corrections, our compositional measurements agreement between the various techniques. Nuclear reaction analysis, Fourier transform infrared spectroscopy, and secondary ion mass spectrometry (SIMS) all yield similar hydrogen contents, within ± 20% for each sample. Electron probe micro-analysis (EPMA) and SIMS yield silicon and germanium contents within ± 7% of each other with results being confirmed by Rutherford backscattering. EPMA oxygen measurements are affected by highly oxidized surface layers, thus these data show larger O concentrations than those measured by SIMS.

The effect of film tensile stress on crystallite nucleation and growth in thermally annealed a-Si:H

“…22 The substrate temperature of these depositions was 230 C, resulting in a film H content (C H ) of $12 atomic percent; the infrared spectroscopy methodology and the proportionality constant used to determine the film C H have been discussed elsewhere. 23 The HWCVD films, of similar film C H , were deposited using a 0.5 mm diameter W filament, a substrate to wire distance of 5 cm, and a filament temperature of $ 2000 C. 24 The film thicknesses investigated for both sets of films was 0.11 lm. Films were isothermally annealed in air at temperatures between 540 C and 600 C (20 C intervals) using a box furnace, with the furnace temperature (T a ) calibrated with a thermocouple placed at the sample position in the furnace.…”

“…The existence of a reduction in film stress around these macroscopic features was confirmed by l-Raman measurements of the crystallite transverse optical (TO) peak position relative to that of c-Si. [22][23][24] By counting the crystallites versus anneal time close to and far away from these surface features, nucleation rate data for stressed and stress relieved areas on the same film were reported. Reasons were proposed for the large lateral distance (100-150 lm) away from these features over which this stress relief was observed.…”

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

“…Each spectrum was then corrected for CO 2 artifacts using previously generated reference spectra, followed by manual baseline correction to remove sinusoidal fringes. The C H was calculated from the Si-H wag mode using a proportionality constant discussed elsewhere [49]. For the X-ray linewidth measurements, a standard Bragg-Brentano geometry was used, with Cu-K a X-rays selected with a graphite crystal monochromator.…”

Amorphous SiGe:H Thin Film Solar Cells with Light Absorbing Layers of Graded Bandgap Profile

“…The bandgap energy (E g ) of an a-SiGe:H film could be reduced from approximately 1.8 to 1.55 by simply increasing the content of Ge from 0 to 20%. 9 However, the use of a-SiGe:H with Ge content exceeding 20% is not recommendable, as it has been reported to result in greater light-induced degradation than that associated with a-Si:H. The bonding energy of Ge-H is weaker than that of Si-H and the attachment of H to Si is preferential over Ge. 9 The light conversion efficiency of a-SiGe:H single junction solar cells has been reported to be generally lower than that of a-Si:H cells due to the defects generated by the incorporation of Ge, whose atomic radius (0.125 nm) is 13.6% larger than that of Si (0.11 nm).…”

“…9 However, the use of a-SiGe:H with Ge content exceeding 20% is not recommendable, as it has been reported to result in greater light-induced degradation than that associated with a-Si:H. The bonding energy of Ge-H is weaker than that of Si-H and the attachment of H to Si is preferential over Ge. 9 The light conversion efficiency of a-SiGe:H single junction solar cells has been reported to be generally lower than that of a-Si:H cells due to the defects generated by the incorporation of Ge, whose atomic radius (0.125 nm) is 13.6% larger than that of Si (0.11 nm). Therefore, earlier studies on SiGe solar cells mostly involved the deposition of SiGe films of low defect density or the fabrication of cells showing low light-induced degradation.…”