| Summary: | 碩士 === 中原大學 === 電子工程研究所 === 92 === Indium tin oxide (ITO) that has unique characteristics of good conductivity and high light transmission over the visible spectrum is the most widely used as the transparent conducting electrode to the applications of optoelectronic devices. This thesis will employ rapid thermal annealing (RTA) process to investigate the characteristics and the performance of ITO films on AlGaInP light emitting diodes (LEDs). The main device structure is shown schematically in Fig.1.
First, ITO was individually deposited on p+-GaAs with concentration of about 1× 1019 cm-3 、semi-insulated GaAs and glass substrates by E-beam evaporation method. ITO disks were bombarded by two kind of In2O3/SnO2 composition ratios (90/10 or 95/5) employed as a target. ITO films were treated using RTA in the hydrogen and nitrogen ambient, respectively. After annealing in the H2 ambient, the lower specific contact resistivity ρc and sheet resistivity Rsh were obtained, but the transmittance of ITO films were even low. In the N2 ambient, a high transmittance more than 90% was obtained, because of the introduction of oxides. Besides, different ratios of ITO target also influence the optical and electrical characteristics. ITO films (In/Sn=90/10) exhibited better electrical characteristics and ITO films (In/Sn=95/5) present better optical characteristics.
After the measurements of the optical and electrical characteristics, evaporated transparent conducting Indium-tin oxide (ITO) layers are
utilized as the window material and the current spreading layer on AlGaInP light emitting diodes (LEDs). ITO films of thickness 50nm revealed the specific contact resistivity ρc of about 1~5×10-4Ω-cm2 and the transmittance of up to 90% in the visible spectral region, which were used for AlGaInP light emitting diodes (LEDs). It can be seen that ITO-coating LEDs demonstrate better I-V characteristics and smaller full width at half maximum (FWHM) than LEDs without ITO. Besides the devices incorporated with the ITO layer annealed in the N2 ambient above 400oC give a marginally greater output than the conventional non-ITO devices. It was suggested that the developed typical process will improve nowadays commercial LEDs.
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