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Visible-Light Injection-Electroluminescent a-SiC / p-i-n Diode

A new type of visible-light injection-electroluminescent a-SiC diode has been developed. The LED has the structure of p a-SiC/i a-SiC/n a-SiC. Visible white-green, yellowish-orange and red light emissions have been observed for the first time in these junctions at room temperature. It is demonstrated that emitting color can be controlled by choosing the optical band gap of the luminescent active i a-SiC layer. The brightness of the yellowish-orange emission was 0.13 cd/m2 with a forward injection current density of 200 mA/cm2 for 0.033 cm2 cell area.

A study of visible-light injection-electroluminescence in a-SiC/p-i-n diode

Abstract An injection mode electroluminescence has been first observed in a p a-SiC/i a-SiC/n a-SiC diode. White-green, yellowish-orange and red light emissions have been observed in these junctions at room temperature depending on the optical band gaps of the luminescent active i layers. From the relation between the injection current density and the total EL intensity, it has been shown that EL is dominated by the recombination of electron-hole pairs doubly injected into the i layer.

Carrier injection mechanism in an a-SiC p-i-n junction thin-film LED

A systematic study has been done on the carrier injection mechanism and electroluminescent properties of an amorphous silicon-carbide p-i-n junction thin-film light-emitting diode (a-SiC TFLED). The analysis of the junction characteristics reveals that the main contribution to the junction current comes from electrons injected by tunneling from the n-layer through the i-n interface notch barrier, while the electroluminescent property of the TFLED is determined by the injection process of holes. This process also takes place by tunneling, in this case from the p-layer through the p-i interface notch barrier. On the basis of the results of the analysis, a method to improve the LED performance using a hot-carrier-tunneling injector structure is proposed. With this structure, the brightness of the TFLED is increased by more than one order of magnitude to about 20 cd/m/sup 2/, with an injection current density of 600 mA/cm/sup 2/. >

Improvement of carrier injection efficiency in a-SiC p-i-n LED using highly-conductive wide-gap p, n type a-SiC prepared by ECR CVD

Abstract Highly conductive and wide band gap p- and n- type a-SiC have been prepared by ECR (Electron Cyclotron Resonance) plasma CVD. By utilizing these wide-gap materials as carrier injector layers in a-SiC p-i-n junction LED, the EL intensity is increased by more than one order of magnitude with increasing the energy gap of the injector layers, and at the same time the EL spectra shift towards shorter wavelength. These improvements are attributed to the increase in the carrier injection efficiency.

Amorphous Visible-Light Thin Film Light-Emitting Diode Having a-SiN:H as a Luminescent Layer

Hydrogenated amorphous silicon nitride (a-SiN:H) has been applied for the first time as a luminescent active layer (i-layer) in an amorphous visible-light thin film light-emitting diode (TFLED). The TFLED has the structure of glass substrate/ITO/p a-SiC:H/i a-SiN:H/n a-SiC:H/Al. Visible red and yellow emissions can be observed at room temperature from the TFLEDs in which the optical energy gap of i-a-SiN:H is larger than 2.4 eV. The brightness of the red TFLED was 0.5 cd/m2, with a forward injection current density of 2000 mA/cm2 for the 0.033 cm2 cell area.

Highly conductive p-type microcrystalline SiC:H prepared by ECR plasma CVD

Highly conductive p-type microcrystalline SiC:H films have been prepared by ECR (electron cyclotron resonance) plasma CVD. The material with an optical energy gap of 2.25 eV exhibits a dark conductivity as high as 10 S cm-1 which is more than seven orders of magnitude higher than that of amorphous SiC:H prepared by conventional RF plasma CVD. The optimal energy gap can be controlled in the range from 2.0 to 2.8 eV, while retaining excellent conductivity. Utilizing this material as a wide-gap heterojunction contact in amorphous silicon solar cell, a conversion efficiency of 12.0% has been obtained with a large open circuit voltage.

Valency control of P-type a-SiC:H having the optical band gap more than 2.5 eV by electron-cyclotron resonance CVD (ECR CVD)

Abstract Electron Cyclotron Resonance plasma CVD (ECR CVD) has been used to prepare highly conductive and wide band gap a-SiC:H of p-type conduction. A conductivity higher than 10−1 Scm−1 has been obtained with an activation energy as small as 0.05 eV for p-type a-SiC:H having the band gap in the range from 2.0 eV to 2.9 eV. The high conductivity is found to be due to the formations of microcrystalline Si and SiC.

Detailed studies of optical edge and below gap absorption in a-Si1−xCx:H system

Abstract The optical absorption edge and below gap absorption of a-Si 1−x C x :H system are investigated by photoacoustic spectroscopy and electroabsorption method. Incorporation of carbon atoms introduces the broadening of Urbach tail and increasing of below gap absorption. The effect of substrate temperature is also demonstrated. A strong correlation between Urbach slope and shape of electroabsorption spectra are shown and discussed on the stand point of thermal and compositional disorder.

Visible light thin film LED made of a-SiC p-i-n junction

Abstract A visible-light injection-type electroluminescence thin film diode made of amorphous silicon carbide p-i-n junction (a-SiC TFLED) has been developed. The emission color can be controlled from red to yellow by adjusting the optical energy gaps of the luminescent i-layer and the carrier injector p-layer. A brightness of 10 cd/m 2 has been obtained in a yellow emission LED at an injection current density of 100 mA/cm 2 and a forward bias of 10 V. A series of technical data on the device fabrication technology is presented. As a result, an improvement of carrier injection efficiency by utilizing wide-gap p- and n-a-SiC prepared by ECR (electron cyclotron resonance) plasma CVD as well as a possibility of the application of a-SiC TFLED to OE-IC are demonstrated and discussed.

Steady‐state and time‐resolved photoluminescence in microcrystalline silicon

A systematic investigation has been made on steady‐state and time‐resolved photoluminescence (PL) in microcrystalline silicon (μc‐Si) at liquid‐helium temperature. The steady‐state PL spectra on various grain sizes and volume fractions are examined. It is found that the low‐energy emission (∼0.76 eV) arises only from the amorphous phase and not from the crystalline phase and the grain boundary regions. The results indicate that the origin of the luminescence is considered to be due to defects created in the amorphous phase resulting from the microcrystallinity which increase with the grain size and/or the volume fraction. It has been shown from the analysis of the time‐resolved PL measurement that the recombination transition of carriers of the low‐ and the high‐ (∼1.24 eV) energy emissions can be interpreted by a new model.