PECVD grown hydrogenated polymorphous silicon studied using current transient spectroscopies in PIN diodes

Hydrogenated polymorphous silicon (pm-Si:H) has steadily emerged as a potential replacement of hydrogenated amorphous silicon. Possible changes in the density of gap states due to the presence of crystallites is of central importance in understanding steady state and dynamic characteristics of devices using these materials. We have studied a-Si:H and pm-Si:H grown by PEC VD at optimized conditions through the measurement of the steady state reverse current and their transients in PIN devices. The transients are analyzed using isothermal spectroscopic techniques such as Time Analyzed Transient Spectroscopy (TATS), and high resolution Laplace DLTS as a function of temperature. In case of a-Si:H, we obtain the expected signature of emission from a broad density of states in the form of stretched exponentials. In contrast the corresponding spectra for pm-Si:H are dominated by nearly exponential fast current decay processes with discrete energies between 0.20 and 0.26 eV. It is shown that the study of the density of states by dynamic methods such as transient techniques reveal features not accessible to steady state measurements.