(A) study on fabrication of visible P-I-N type thin-film light-emitting diode using photo chemical vapor deposition and its performance Improvement

Abstract

Fabrication of visible a-SiC:H-based p-i-n type thin-film light-emitting diodes (TFLEDs) using a photo-CVD method is proposed. a-SiC:H films, the important luminescently active i layer of the TFLEDs, are prepared by a direct photo-CVD method from a gas mixture of disilane and ethylene. a-SiC:H films have a bandgap enough to be applicable to the luminescently active i layer of the TFLEDs and also show good photoluminescence characteristics. In these diodes, p-mc-Si:H and n-mc-Si:H films were used as hole and electron injectors into the luminescently active i layer, respectively. The fabricated visible a-SiC:H-based p-i-n type TFLED has a vertical structure of glass/$SnO_2$ (F-doped)/p-$\mu c$-Si:H (2.3 eV)/i-a-SiC:H (3.0 eV)/n-mc-Si:H (2.4 eV)/Al. It has a threshold voltage of 6V and electroluminescence (EL) peak wavelength of 700 nm emitting reddish light as detected by the naked eyes. To enhance the efficiency of hole injection into the luminescently active i layer, a HTI layer was inserted at the p/i interface. It is found that inserting the HTI layer increases the efficiency of hole injection, improving the performance of the TFLEDs. The obtained optimum thickness of the HTI layer was 3.0 nm. Then, the effect of thickness and bandgap of p-$\mu c$-Si:H layer on the performance of TFLEDs was investigated. Increasing the bandgap of p-layer decreases the height of notch barrier between p-$\mu c$-Si:H and HTI layers, resulting in injection of the more amount of holes to be injected into the luminescently active i layer. Then, to improve the device performance by decreasing the amount of carriers trapped by defect states at the HTI/i interface, the HTI layer was graded. Such a grading was obtained by decreasing the flow rate of hydrocarbon gas (i.e. ethylene) from a predetermined value to zero during deposition of the layer. The visible a-SiC:H-based p-i-n type TFLEDs with a graded-gap HTI layer showed better device characteristics than those with a nongraded-gap ...