Nerng-Fu Shin

Graded-gap a-SiC:H p-i-n thin-film light-emitting diodes

To improve the performance of hydrogenated amorphous-silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diodes (TFLEDs), a p-i-n TFLED with a graded p-i junction was proposed and fabricated. The electroluminescence (EL) intensity of the proposed TFLED was more than 100 times higher than that of the basic p-i-n TFLED and about 35 times lower than that of the conventional green LED, at the same injection current density. This significant improvement is attributed to the better interface property and enhancement of hole injection efficiency by using the graded-gap p-i junction.<<ETX>>

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 LEDs (TFLEDs) 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 TFLEDs are presented and discussed. At an injection current density (J) of 600 mA/cm/sup 2/, the brightness (B) of the SG and DG TFLEDs obtained were 30 and 207 cd/m/sup 2/, respectively. This significant improvement of brightness, as compared to those of the previously reported TFLEDs 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 TFLEDs. This implies that the electroluminescence (EL) mechanism of these TFLEDs might be a tail-to-tail-state recombination. In addition, the conduction currents of these TFLEDs 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.

HYDROGENATED AMORPHOUS-SILICON CARBIDE P-I-N THIN-FILM LIGHT-EMITTING-DIODES WITH BARRIER LAYERS INSERTED AT P-I INTERFACE

To improve the electroluminescence (EL) intensity of the hydrogenated amorphous silicon carbide (a-SiC:H) pi-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 1 had a 25 A i-type single-barrier structure and the device II had an i-type double-barrier structure of barrier(10 A)/well(10 A)/barrier(10 A). The obtainable brightness of device I was 342 cd/m 2 at an injection current density of 600 mA/cm 2 . On the other hand, the device II had a brightness of 256 cd/m 2 at 800 mA/cm 2 . These brightnesses were about 3 orders of magnitude higher than that of a basic a-SiC:H p-i-n TFLED

Hydrogenated amorphous silicon carbide double graded-gap p-i-n thin-film light-emitting diodes

Hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diodes (TFLEDs) with graded p/sup +/-i and i-n/sup +/ junctions have been proposed and fabricated successfully on an indium-tin-oxide (ITO)-coated glass. An orange TFLED reveals a brightness of 207 cd/m/sup 2/ at an injection current density of 500 mA/cm/sup 2/. 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 post-metallization annealing, and higher optical gaps of the doped layers.<<ETX>>

Electroluminescence characteristics and current-conduction mechanism of a-SiC:H p-i-n thin-film light-emitting diodes with barrier layer inserted at p-i interface

In order to improve the electroluminescence (EL) characteristics of the hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diode (TFLED), a barrier layer (BL) was inserted at its p-i interface to enhance the hole injection efficiency under forward-bias operation. The a-SiC:H TFLEDs with various optical gaps of BL had been fabricated and characterized. In addition, a composition-graded n/sup +/-layer was used to reduce its series and contact resistances to the Al electrode and hence the EL threshold voltage (V/sub th/) of an a-SiC:H BL TFLED. The highest obtainable brightness of an a-SiC:H BL TFLED was 342 cd/m/sup 2/ at an injection current density of 600 mA/cm/sup 2/ and the lowest EL V/sub th/ achievable was 6.0 V. The current-conduction mechanism of an a-SiC:H BL TFLED had also been investigated. Within the lower applied-bias region, it showed an ohmic current, while within the higher applied-bias region, a space-charge-limited current (SCLC) was observed. >

Visible a‐SiC:H P‐I‐N light emitting diodes with hot‐carrier tunneling injection layers

Abstract The a‐SiC:H thin‐film light‐emitting diodes (TFLEDs) with a basic p‐i‐n structure and the higher mobility‐gap a‐SiC:H hot‐carrier tunneling injection (HTI) layers inserted at the p‐i and/or i‐n interfaces to improve the luminance have been fabricated and characterized. The high mobility‐gap a‐SiC:H HTI‐ and i‐layers were deposited by feeding C2H2 and SiH4 at different ratios, instead of CH4, SiH4 and the appropriate dopant which were employed for the other p‐ and n‐ a‐SiC:H layers, into the chamber of plasma‐enhanced chemical vapor deposition (PECVD) system. It is observed that the Electroluminescence (EL) spectra have a blue‐shift for those TFLEDs with HTI‐layer embedded at the p‐i interface. Experimentally, for TFLEDs with p/HTI/i/HTI/n or p/HTI/i/n structure, visible orange light emission was observed, but, for those with p/i/HTI/n structure, a red one was noticed, at room temperature.

ELECTROLUMINESCENCE OF A-SIC-H P-I-N THIN-FILM LIGHT-EMITTING-DIODES WITH QUANTUM-WELL-INJECTION STRUCTURES

Abstract In order to improve the electroluminescence (EL) characteristics of hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diodes (TFLEDs), the quantum-well-injection (QWI) structures have been incorporated into their intrinsic (i-) layer. Two types of TFLED were fabricated to study the effect of the incorporated QWI structures on their EL characteristics: the device I contains a step-gap QWI structure of barrier (15 A)/well (45 A)/barrier (15 A) inserted at both the p-i and i-n interfaces, and the device II has only one graded-gap QWI structure of barrier (10 A)/well (10 A)/barrier (10 A) inserted at the p-i interface. The obtained brightness of device I was about 10 cd/m2 at an injection current density of 1 A/cm2. The emission light of device I was yellow-like as detected by human eyes. Whereas, for device II, the brightness was about 256 cd/m2 at 800 mA/cm2 and an orange light emission was observed.

Graded-Gap and Quantum-Well Injection a-SiC:H p-i-n Light-Emitting Diodes

As alternative approaches to improve the performance of hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diodes (TFLED’s), graded p-i junction and quantum-well-injection (QWI) structures have been incorporated into the i-layer of p-i-n TFLED’s. The electroluminescence (EL) intensity of TFLED’s with graded p-i junction is 100 times higher than that of basic p-i-n TFLED’s and about 35 times lower than that of conventional green LED’s at the same injection current density. The EL intensity of QWI TFLED’s is also 20 times higher than that of basic p-i-n TFLED’s. For graded-gap TFLED’s, a red-orange light emission was experimentally observed by naked eyes, while for QWI TFLED’s a yellow-like one was observed.

Characteristics and analysis of a-Si:H color-sensitive photodetectors

A novel a-Si:H photodetector has been demonstrated. The advantages of this photodetector include a voltage-adjustable sensitive-wavelength range, which has been confirmed by simulation results, and a lower sub-peak spectral response. The performances of the successfully fabricated a-Si:H color-sensitive photodetectors, processing a minimum FWHM (full width at half maximum) of 600 AA in its spectral responses and with the basic structure of Al/n/sup +/-i-p/sup +/-i-n-i-p-i-n/sup +//ITO(indium tin oxide)/glass, have been quantitatively fitted by the theoretical analysis. The simple model presented can be used to explain the color-sensitive features observed experimentally for the proposed photodetectors.<<ETX>>