PHOTOLUMINESCENCE INVESTIGATION OF A-C-H THIN-FILMS

The photoluminescence (PL) properties of undoped and aluminum-doped hydrogenated amorphous carbon (a-C: H) thin films with optical gaps of greater than 3 eV were investigated. Optical absorption, PL and secondary ion mass spectroscopy were used to characterize the films. The results from the PL investigation showed that the PL spectral shape was sensitive to the excitation wavelength, and the PL intensity was dependent on time and decreased or fatigued with increasing time of exposure. Films with aluminum doping demonstrated an increased PL fatigue rate compared with undoped samples. The ''bleaching'' of the a-C: H PL emission, caused by continuous Ar+ illumination, was found to be reversible at room temperature by discontinuing laser illumination for 48 h. Comparison of the PL intensity time dependence of the doped samples showed a power law dependence similar to that previously reported in hydrogenated amorphous silicon (a-Si: H). For the two doped films, the time dependence of the PL intensity was found to be proportional to t-0.29 and t-0.33 for t > 400 s. If the kinetic mechanisms are similar, the principal fatigue mechanism in the doped films can be attributed to the reversible photo-induced creation of dangling bonds.