DEFECT EQUILIBRATION AND INTRINSIC STRESS IN UNDOPED HYDROGENATED AMORPHOUS-SILICON

Relaxation data for the thermal equilibrium defect densities in undope d a-Si:H are obtained by time-of-flight (TOF) measurement in the tempe rature range of 160-degrees to 250-degrees-C. The internal stress in t he material is also measured. The mobility-lifetime product of electro ns (mutau) increases from 0.50 X 10(-7) to its equilibrium value of 2. 24 X 10(-7) cm2/V during the 160-degrees-C annealing. The equilibrium value of mutau is equivalent to the spin density (N(s)) of 1.12 x 10(1 5) cm-3. The N(s) curves have a minimun value just before their equili brium. The time dependence of the N(s) relaxation follows a two-term s tretched exponential form which corresponds to two metastable states, and each relaxation time is activated with activation energies of 1. 1 0 to 1. 20 eV. The thermal equilibrium N(s) increases with temperature with an activation energy of 0.20 to 0.30 eV. The data for the second annealing at 160-degrees-C after the first long annealings at 200-deg rees and 250-degrees-C also follows the two-term stretched exponential form derived from the first annealing data. The result suggests the p resence of a multivalley energy configuration diagram at metastable st ates. The drift mobility of electrons (mu) increases slightly compared with the mutau changes, and no stress change is observed during the v arious annealing steps. It is concluded that the structural change is much smaller than the change in metastable-state densities during anne aling in the temperature range of 160-degrees to 250-degrees-C.