Carrier mobility, band tails and defects in microcrystalline silicon

The development of microcrystalline silicon thin films and devices is briefly reviewed. Transport mechanisms, and the attendant key parameters of carrier mobility, band-tail width and defect density, are linked to film structure and composition. In particular we discuss the wide (but systematic) variations in time-of-flight mobility and its unusual field-dependence. While microcrystalline silicon remains an inferior semiconductor to single-crystal silicon, we propose, and support by means of a computer model, that present device-grade material may be of sufficient quality to justify re-examining whether useful thin-film bipolar devices might be developed. These could find application as more sensitive photo-detectors, and as current drivers in organic LED displays and logic circuits.