Correlation of structural inhomogeneities with transport properties in amorphous silicon germanium alloy thin films

Amorphous silicon–germanium (a-Si1−xGex:H) alloy thin films were studied over a wide range of Ge content (x=0–1.00) grown by radio frequency plasma CVD (rf PECVD) technique with variation of different deposition parameters such as H2 dilution, rf power and square wave pulse modulation (SWPM) of rf amplitude. Structural properties like microstructure factor (R⁎) and AFM surface roughness (RRMS) were correlated with the transport properties such as mobility-lifetime product (μτ) and ambipolar diffusion length (Ld) of these films. Near the middle composition range (x=0.32–0.70), the R⁎ in these films varies between 0.20 and 0.42 and Ld ranges between 50 and 60 nm. Films deposited near the pure silicon and pure germanium ends have improved structural and transport properties. By SWPM method we have been able to significantly lower the R⁎ value of the a-Si1−xGex:H films to 0.15 with x=0.40–0.45 resulting in Ld=100 nm and μτ=1.0×10−6 cm2 V−1.