FABRICATION OF HIGHLY STABLE AND LOW DEFECT DENSITY AMORPHOUS-SILICONFILMS AT LOW SUBSTRATE-TEMPERATURE BY PLASMA CHEMICAL-VAPOR-DEPOSITION ASSISTED WITH PIEZOELECTRIC VIBRATION

Plasma chemical vapor deposition (CVD) of a-Si:H films has been conduc ted under the application of piezoelectric vibration to the substrates with the expectation of enhancing the surface migration of the precur sors. Defect density of the order 10(15) cm(-3) was achieved for a fil m deposited at 120 degrees C under 2 MHz piezoelectric vibration. The photodegradation behavior of the deposited films was measured using ir radiation by pulsed ruby laser as well as by Xe lamp. The prolonged li ght soaking increased the defect densities in the a-Si:H films as well as those in the films deposited by the conventional method, i.e., wit hout the piezoelectric vibration. However, the saturated value for the former films remained at 3 x 10(16) cm(-3), significantly lower than the value (similar to 10(17) cm(-3)) for the latter. The activation en ergy for recovery from the light-induced defect of a-Si:H was higher f or the film deposited with piezoelectric vibration than the film depos ited without the vibration. Thus, the piezoelectric vibration apparent ly functioned not only to reduce the defect density in as-deposited fi lms but also to improve the stability against light soaking.