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+ junctions have been proposed and fabricated successfully on an indium-tin-oxide (ITObcoated glass. An obtained orange TFLED reveals a brightness of 207 cd / m 2 at an injection current density of 600 mA / cm2, which is the brightest one ever reported for a-SiC:H TFLED's at the same injection current density. This significant increase of brightness could be ascribed to the combined effect of reduced interface states by using the graded-gap junctions, lower contact resistance due to postmetallization annealing, and higher optical gaps of the doped layers.

To improve the electroluminescence (EL) intensity of the hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diode (TFLED), a barrier-layer (BL) structure had been inserted at its p-i interface and used to enhance the hole injection efficiency of TFLED under forward-bias operation. Two TFLEDs with different BL structures were studied. The device I had a 25 Å i-type single-barrier structure and the device II had an i-type double-barrier structure of barrier(10 Å)/well(10 Å)/barrier(10 Å). The obtainable brightness of device I was 342 cd/m2 at an injection current density of 600 mA/cm2. On the other hand, the device II had a brightness of 256 cd/m2 at 800 mA/cm2. These brightnesses were about 3 orders of magnitude higher than that of a basic a-SiC:H p-i-n TFLED.

A-SiC:H p-in thin-film LED's (TFLED's) containing a single graded-gap p-in junction (SG) or double graded-gap p-in and in 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 2 , the brightness (B) of the SG and DG TFLED's obtained were 30 and 207 cd/m 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 2 , could be ascribed to the reduced interface states with the graded-gap junctions, lower contact resistance between ITO and player due to a plasma treatment of ITO prior to player deposition, post metallization annealing of thermally evaporated Al on n-layer, and higher optical gaps (Eopt's) of the doped layers employed. The slopes of the nearly linear B-J relationships show the 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.

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