Optical properties of amorphous silicon germanium obtained by low-frequency plasma-enhanced chemical vapor deposition from <inline-formula><math display="inline" overflow="scroll"><msub><mi>SiH</mi><mrow><mn>4</mn></mrow></msub><mo>+</mo><msub><mi>GeF</mi><mrow><mn>4</mn></mrow></msub></math></inline-formula> and from <inline-formula><math display="inline" overflow="scroll"><msub><mi>SiH</mi><mrow><mn>4</mn></mrow></msub><mo>+</mo><msub><mi>GeH</mi><mrow><mn>4</mn></mrow></msub></math></inline-formula>

Abstract

Amorphous silicon germanium (a-Si1–xGex) thin films are prepared by low-frequency plasma-enhanced chemical vapor deposition (LF PECVD) on glass substrates, from SiH4+GeF4 and SiH4+GeH4. These films are deposited under capacitive discharge during 60 min, at a frequency of 110 kHz, substrate temperature of 300°C, pressure of 0.6 Torr, and power of 350 W. The germanium gas mixture composition, determined by XGe=[GeF4]([GeH4])/[SiH4]+[GeF4]([GeH4]), is varied from 0 to 1. These films are deposited from a (1–XGe)SiH4+(XGe)GeF4(GeH4) mixture, with H2 dilution. The refractive index n and absorption coefficient are determined from transmission spectra. The optical energy gap is also determined. The influence of gas sources on the optical parameters is discussed.