A three-dimensional model with finite difference and time domain was established to investigate the enhancement of the light output intensity of GaN light-emitting diodes ͑LEDs͒ with bottom pillar ͑BP͒ structure. Through comparing the normalized light extraction intensity of GaN LEDs with or without BP in different dimensions, the theoretical results show that the light output intensity in the LED with BP structure involved could be enhanced by about 30%. The influence of BP structure on the light output intensity of a LED could be explained by the physical model of light interaction. In addition, the experimental results also show the same trend to the theoretical calculations.
Effect of composite collector design on the breakdown behavior of InGaP/GaAs double heterojunction bipolar transistor J. Appl. Phys. 93, 605 (2003); 10.1063/1.1521513Analysis of collector-emitter offset voltage of InGaP/GaAs composite collector double heterojunction bipolar transistor Two significantly abrupt increases of dc current gain ͑͒ at the opposite extremes of base-emitter voltages (V be ) linked by a relatively slight increase of  in the range of 1.25рV be р1.75 V are found in InGaP/GaAs heterojunction bipolar transistors ͑HBT's͒. It has been proved that the burn-in effect directly causes the second abrupt increase of  occurring at V be Ͼ1.75 V instead of elsewhere. In addition, choosing V be Ͼ1.75 V, a higher base-emitter voltage results in a faster increase rate with improvement in current gain transient. Based on these observations, a constant period of voltage stress ͑CPVS͒ with V be ϭ2.0 V and V ce ϭ3.0 V for 5 min with a specific choice of V be Ͼ1.75 V ͑the voltage range corresponding to the second abrupt increase of ͒ is thus applied to promote the electrical performance of HBT's. After applying a CPVS, the burn-in effect is substantially suppressed without showing any second abrupt increase of current gain. Although the current measured under both reverse and forward biases is greatly reduced for the base-emitter junction, a CPVS slightly degrades the electrical properties of a base-collector junction. Also, it has been proved that bulk recombination, rather than the surface recombination current, the base contact recombination, or the space-charge recombination, is the dominant base current component causing the burn-in effect. The electrical improvement of the base-emitter junction is due to the annihilation of H-related traps in the base region after a CPVS. Once H Ϫ ions form, we propose that these ions are too fast to drift toward the base-collector junction under the reverse bias of the base-collector voltage. After migration through the extrinsic base region, H Ϫ ions are supposed to be trapped near the base-collector space region, which results in the degradation of the base-collector junction after a CPVS.
Different from the single-barrier Wentzel-Kramer-Brillouin tunnelling and thermionic emission models, the dark current of bound-to-continuum quantum-well infrared photodetectors is theoretically studied by the new approach of the field-induced mixing effect (FIME). Based on the rate balance condition between the loss rate of bound electrons caused by FIME and the net quantum capture of continuum electrons, the Fermi levels of continuum and bound electrons are separated with each other at non-zero bias. In addition to showing good agreement with the experimental results without parameter fitting techniques, the variations of dark current with both operating temperature and voltage bias can also be explained by the Fermi level of continuum electrons. With a current suppression ratio to reveal the variations of dark current with structural parameters, the ratio and the temperature region where the dark current is effectively suppressed are both diminished as the bias increases.
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