Electrical and luminescent characteristics of a-SiC:H p-i-n thin-film LED'S with graded-gap junctions

a-SiC:H p-i-n thin-film LED's (TFLED's) containing a single graded-gap p-i-n junction (SG) or double graded-gap p-i-n and i-n junctions (DG) have been postulated and fabricated successfully on indium-tin-oxide (ITO)-coated glass substrates, with a plasma-enhanced chemical vapor deposition (PECVD) system. Some important characteristics and related physics of these two types of TFLED's are presented and discussed. At an injection current density (J) of 600 mA/cm/sup 2/, the brightness (B) of the SG and DG TFLED's obtained were 30 and 207 cd/m/sup 2/, respectively. This significant improvement of brightness, as compared to those of the previously reported TFLED's with a highest brightness of 20 cd/m/sup 2/, could be ascribed to the reduced interface states with the graded-gap junctions, lower contact resistance between ITO and the p-layer due to plasma treatment of ITO prior to p-layer deposition, post metallization annealing of thermally evaporated Al on n-layer, and higher optical gaps (E/sub opt/'s) of the doped layers employed. The slopes of the nearly linear B-J relationships show a diode factor very close to unity for the fabricated SG and DG TFLED's. This implies that the electroluminescence (EL) mechanism of these TFLED's might be a tail-to-tail-state recombination. In addition, the conduction currents of these TFLED's are almost temperature dependent, and that of the DG TFLED might consist of an ohmic current and a space-charge-limited current (SCLC) within the lower and higher applied-bias regions, respectively.