Electronic properties of GeySi1−y:H films deposited by LF PECVD at low temperatures

This paper reports the study of Ge_ySi_1-y:H films deposited at temperatures in the range of T_d= 70 to 300°C. The films were grown in capacitive low-frequency (f=110 KHz) discharge from Si:H₄ and Ge:H₄ feed gases diluted with H₂. Other parameters were as follow: hydrogen flow Q_H2= 3750 sccm, silane flow Q_SiH4=50 sccm, germane flow Q_GeH4= 500 sccm hydrogen dilution ratio R= Q_H2/(Q_SiH4+Q_GeH4)=75, discharge power W= 300 Watt and pressure P= 0.76 Torr. The deposition rate of the films was varied not monotonically in the range of Td from 70 to 300°C. Hydrogen bonding was characterized by Fourier transform infrared (FTIR) spectroscopy. The electrical parameters were extracted from the measurements of temperature dependence of conductivity σ(T). Activation energy and room temperature conductivity of the films were observed in the range of the values E_a=0.27 to 0.37 eV and σ_RT=5.7 × 10^-5 to 9.6 × 10^-4 Ω^-1 cm^-1, respectively. The electronic properties characterized by different electrical and optical measurements showed optimal properties within the deposition temperature range T_d~160°C to 220°C