Better metal electrode can be obtained by heat treatment which causes deeper diffusion of metal particles into the (Pb, Bi)SrCaCuO superconductor to improve contacts between metal electrodes and the sample. However, high-T
c phase of the specimen was destroyed at 700°C and the sample showed semiconducting behaviour. Low room temperature contact resistivity was obtained about 3.21×10-4 (Ω-cm2) and 2.34×10-6 (Ω-cm2) at 77 K for a sample with evaporating silver electrodes and annealed at 600°C for 2 hours. Non-ohmic contacts are observed for the indium and aluminum terminals.
By inductively coupled plasma (ICP) etching, a selective high barrier region (SHBR) was fabricated below the p-pad metal electrode for modifying the injection current distribution on p-type GaN of GaN-based light-emitting diodes (LEDs). Through the analysis of current noise power spectra, the samples with ICP etching treatment have excess nitrogen vacancies at the selectively etched surface of p-type GaN; thus, they have a lower hole concentration than the as-grown sample, resulting in a larger barrier height for carrier transport. With this SHBR, the light-output power for the LED chip measured at 20 mA was significantly increased by 12% as compared with that for the conventional LED chip. The light-output power increase could be attributed to a relative reduction in optical power absorption under the p-pad electrode and a higher density of current effectively injected into the active layer of the LED by the SHBR structure.
In this paper, we describe the improvement in the light extraction efficiency of AlGaInP light-emitting diodes (LEDs) upon use of a porous anodic alumina (PAA) film and pore widening. Acting as an intervening layer between air and the GaP window layer, PAA increased the critical angle to reduce the internal light reflection of LEDs. The nanopores of the PAA film provided a rough surface that enhanced the light output extraction. These factors resulted in the LEDs with PAA films exhibiting a light output power 29% higher than that of a conventional LED (without PAA film). Furthermore, following a pore-widening treatment for 40 min, the light output improvement increased to 39%. Therefore, the use of PAA film and a suitable pore-widening treatment increases the light extraction efficiency of LEDs.
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