PHOTOCONDUCTIVE ANALYSIS OF DEFECT DENSITY OF HYDROGENATED AMORPHOUS-SILICON DURING ROOM-TEMPERATURE PLASMA POSTHYDROGENATION, LIGHT SOAKING, AND THERMAL ANNEALING

The photoconductivity (sigma(ph)) of thin (less than or equal to 1000 Angstrom) hydrogenated amorphous silicon films (a-Si:H) was measured a s a function of time to monitor the defect density during remote induc tively coupled plasma (ICP) posthydrogenation at room temperature, lig ht soaking (performed both before and after posthydrogenation), and is othermal annealing (performed after posthydrogenation and light soakin g), and fitted to a stretched exponential curve. A decrease of sigma(p h)(t) during posthydrogenation at room temperature was observed and re lated to the breaking of Si-Si weak bonds by individual hydrogen atoms . Upon thermal annealing, the initial equilibrium defect density was r ecovered. The stretched exponential parameters beta and tau of sigma(p h)(t) were the same for the isothermal anneals performed after light s oaking and after plasma posthydrogenation, indicating that the defects introduced in both cases were of similar nature. The stretched expone ntial parameters beta and tau of sigma(ph)(t) were also the same for t he light soaking before and after plasma posthydrogenation, suggesting that posthydrogenation did not alter the susceptibility of the materi al to light-induced degradation. a-Si:H samples deposited by remote IC P, hot-wire, and rf glow discharge were studied. The increase of hydro gen concentration in the samples during posthydrogenation was measured by infrared spectroscopy.