In situ optical emission spectroscopy diagnostics of glow discharges in SiH4/GeH4/H2

Abstract

An optical emission spectroscopic study identifies transient and steady-state behavior of the excited H^*_α/H^*_β/SiH*/GeH* emission in parallel plate SiH₄/GeH₄/H₂ plasma. The effect of deposition parameters on the radical density in plasma is determined. To clarify the radical production mechanism further, the optoelectronic properties of the hydrogenated amorphous silicon–germanium thin films deposited at different hydrogen flow rates in 3 Torr pressure are investigated. The results show a low hydrogen flow rate improves the optoelectronic properties of the thin films whereas a high flow rate leads to a much higher defect density in the thin films. The ratio of GeH* to SiH* emission intensity is related to the germanium content in the plasma. The germanium content is changed for the different hydrogen flow rates, thereby adjusting the optical bandgap, with 1.32 ± 0.20 eV at a high 200 sccm hydrogen flow rate.