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Jongin Shim,Kyungyul Yoo 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.2
A measurement method for the linewidth enhancement factor of a semiconductor Fabry-Perot (FP) laser operating above threshold is presented. This measurement method is designed to have a simple structure and an extend operational range. The active carrier density of the FP laser is modulated by optical injection locking, which makes it possible to measure the variation of optical spectrum from the injected optical frequency.
Sungmin Hwang,심종인,Kyungyul Yoo 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1
We present a planar InGaAs/InP separated absorption, grading, charge, and multiplication (SAGCM) avalanche photodiode (APD) with a thin multiplication layer of 0.2 μm in thickness operating up to 10 Gb/s. It has two floating guard rings (FGRs) and a deep floating ring (DFGR). The multiplication layer thickness and the doping concentration of the charge layer are carefully designed in terms of both the gain and the bandwidth by utilizing the nonlocal model. The simple fabrication processes of recess etching and one-step diffusion are applied. The experimental results show good agreement with the design. Superior characteristics, such as a large gain-bandwidth (GB) product of above 110 GHz, a low dark current of less than 1 nA at 90 % of the breakdown voltage, and a uniform 2-dimensional gain profile within the active region, are obtained.
Dong-Hyun Jang,심종인,KyungYul Yoo 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6
The light extraction efficiency of GaN-based light-emitting diodes (LEDs) is theoretically analyzed by using the ray tracing method. In this model, each material consisting of a LED is characterized by using two main parameters, the refractive index and the optical absorption coefficient, in order to evaluate the light extraction efficiency. This analytical approach is sequentially applied to various enhancement methods, such as a patterned sapphire substrate (PSS), side-surface texturing (SST) and chip shaping, to come up with the most efficient method. The hemisphere PSS turns out to provide a higher light extraction efficiency than the cone and the cylinder PSS. The saw-shaped SST and lozenge-type chip-shaping method are shown to improve the light extraction efficiency from that for a conventional LED. Combinations of two different enhancement methods are also investigated and some combinations are found to contribute significantly to the increase in the light extraction efficiency.
Effect of electrode pattern on light emission distribution in InGaN/GaN light emitting diode
Hwang, Sungmin,Yoon, Joosun,Shim, Jongin,Yoo, Kyungyul WILEY-VCH Verlag 2008 Physica status solidi. PSS. C, Current topics in s Vol.5 No.6
<P>The effect of geometrical electrode pattern on the blue InGaN/GaN multi-quantum well (MQW) light emitting diode (LED) devices is investigated both theoretically and experimentally. A 3-dimensional circuit model of an LED is constructed and then the corresponding circuit parameters are extracted. Circuit parameters of an LED consist of the resistances of the metallic film and epitaxial layer, and intrinsic diodes representing the light-emitting active region. Both the transmission line model (TLM) and current-voltage (I-V) characteristics of LED are employed to extract circuit parameters experimentally. These circuit parameters are then applied to the circuit model to generate light emission patterns in a top-surface emitting-type LED. Experiment results verify that the emitting light distribution from fabricated LED coincides reasonably well with the theoretical results. This makes it possible to design an LED theoretically and predict its actual properties. The LED structure proposed using the model is shown to exhibit not only good light uniformity, but also higher light output power and lower voltage drop. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>