P-of Gan Transparent Electrode

Light Emitting Diode (LED) is a cool lamp with small bulk, low energywasted, quick time responded, high reliability and long life; it has alreadybeen widely used in photoelectric system. With the characteristic such aslarge band gap and good thermal stability, GaN base is the ideal material forhigh power LED with the range of spectrum from violet to green. During thelatest ten years the GaN-based blue and white LED was got quickdevelopment, and it will replace the conventional lamp such as incandescentand fluorescent and be available in general illumination. However, there arestill some problems for the production of high power GaN-based LED,including poor thermal dissipation, high resistance of p-GaN ohmic contact,and low lighting efficiency. For p-GaN ohmic contact is usually large in sizein order to ease the resistance, light is blocked and absorbed by the p-GaNohmic contact layer. As a result, the realization of low resistance andtransparent p-GaN ohmic contact are worth being studied on. Nowadays, theNi/Au base metallization has been developed and widely used as a matureway to realize the low resistance p-GaN ohmic contact. In this paper, therefraction index of p-contact developed by Ni/Au base metallization iscalculated; the power flow propagation within the p-contact is analyzed andcoupling layer over the p-contact is designed to reduce light-absorption andreflection by p-contact; effect of different refraction indexes and opticalthicknesses of coupling layer on the transmissivity, reflectivity andabsorption coefficient at 450nm wavelength of coupling layer/p-contactfilms is analyzed to optimize the design of coupling layer; effect of differentincident angles on the transmissivity at 450nm wavelength of couplinglayer/p-contact films is analyzed and frustum of cone structure scheme ofITO layer is applied to attenuating total reflectance (ATR) of the interfacebetween air and ITO, so that light-extraction efficiency of GaN-based LEDcan be increased.In the thesis, some important contents are analyzed strictly as follows:1. The progress of ohmic contact to p-type GaN is rewiewed, in detail, and someadvices put forward about development of low resistance p-GaN ohmiccontact in the future. 2. Effect refraction index of ohmic contact to p-type GaN developed byoxidizing Ni/Au thin films is calculated.3. Power flow propagation within the p-contact is analyzed and couplinglayer over the p-contact is designed to reduce light-absorption and reflectionby p-contact.4. Effect of different refraction indexes and optical thicknesses of couplinglayer on the transmissivity, reflectivity and absorption coefficient at 450nmwavelength of coupling layer/p-contact films is analyzed to optimize thedesign of coupling layer. Result calculated by transfer matrix method showsthat transmissivity of coupling layer/p-contact films at 450nm wavelengthincreases to 75% for the ITO coupling layer with optical thickness of p/2and refraction index of 2.02.5. Effect of different incident angles on the transmissivity at 450nmwavelength of coupling layer/p-contact films is analyzed and frustum ofcone structure scheme of ITO layer is applied to attenuating total reflectance(ATR) of the interface between air and ITO so that light-extractionefficiency of GaN-based LED can be increased.