Electronic traps in mixed Si1−xGexO2 films

Thermally stimulated luminescence (TSL) and infrared (IR) spectroscopy were measured in plasma grown Si1−xGexO2 (x=0, 0.08, 0.15, 0.25, 0.5) with different thicknesses (12–40 nm). A comparison with the TSL properties of thermally grown SiO2 and GeO2 was also performed. A main IR absorption structure was detected, due to the superposition of the peaks related to the asymmetric O stretching modes of (i) Si–O–Si (at ≈1060 cm−1) and (ii) Si–O–Ge (at 1001 cm−1). Another peak at ≈860 cm−1 was observed only for Ge concentrations, x>0.15, corresponding to the asymmetric O stretching mode in Ge–O–Ge bonds. A TSL peak was observed at 70°C, and a smaller structure at around 200°C. The 70°C peak was more intense in all Ge rich layers than in plasma grown SiO2. Based on the thickness dependence of the signal intensity we propose that at Ge concentrations 0.25⩽x⩽0.5 TSL active defects are localised at interfacial regions (oxide/semiconductor, Ge poor/Ge rich internal interface, oxide external surface/atmosphere). Based on similarities between TSL glow curves in plasma grown Si1−xGexO2, thermally grown GeO2 and SiO2 we propose that oxygen vacancy related defects are trapping states in Si1−xGexO2 and GeO2.