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/cm², the brightness (B) of the SG and DG TFLED´s obtained were 30 and 207 cd/m², respectively. This significant improvement of brightness, as compared to those of the previously reported TFLED´s with a highest brightness of 20 cd/m², 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_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