Investigations of the Electro-optical Properties of GaN Nanowires and InGaN LEDs with Different TMIn Treatment Times

• Main Authors: Shi-Kai Lin, 林士凱
• Other Authors: Shih-Wei Feng
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/67mwxa

碩士 === 國立高雄大學 === 應用物理學系碩士班 === 97 === This dissertation consists of two parts：one is optical properties of strained GaN nanowires and the other is the effects of TMIn treatment on the optical and material characteristics of InGaN/GaN p-i-n epilayer and LED device. In the first part, we report GaN nanowires through direct reaction of metal gallium vapor with flowing NH3 on GaN mesas substrate. Four GaN nanowires samples grown from ELO stripes along m-axis were prepared with different NH3 flow rates (20, 40, 60 and 80 sccms). Except for the sample 80 NH3, the density of m-axis nanowires on the c-plane mesa surface increases substantially with higher NH3 flow rate. The luminescence pattern in the CL image is expected to correlate with the nanowire nanostructures. The samples 40 and 60 sccm NH3 show a higher density of GaN nanowires such that the CL images present a higher contrast and stronger intensity. In addition, with a higher NH3 flow rate, the in-plane strains and decreases slightly. This implies a smaller compressive strain along wire growth direction and a smaller tensile strain along the radial direction in the highly NH3-flow-rate sample. Furthermore, the anisotropic in-plane strain can impact the optical property as well as shape distribution of nanowires. From the results of polarized PL results, it was found that the higher the NH3 flow rate, the lower the degree of polarization. Also, a smaller compressive strain along wire growth direction in the highly NH3-flow-rate sample results in a longer length such that a smaller diameter was observed. In the second part, the optical and material characteristics of InGaN/GaN p-i-n epilayer and LED device with TMIn treatment were studied. It was shown that TMIn treatment can improve internal quantum efficiency and enhance luminescence of InGaN/GaN MQW epilayers. With TMIn treatment, both InGaN decomposition and indium aggregation are suppressed such that purer phase, more homogeneous indium composition, less defect density, and better quantum well structures were observed. In addition, TMIn treatment makes the p-i-n epilayers show higher indium composition, stronger green emission, and shorter the recombination decay time. Furthermore, four LED devices with different TMIn treatment times were prepared. With a longer treatment time, the LED device shows stronger EL intensity, narrower EL width, better luminescence efficiency. Also, from the TREL results, the shorter responses times of sample TMIn-180 sec suggests that better quantum well structure helps to carrier relaxation. The better quantum well structure in the TMIn-treated sample helps to carrier recombination. From the viewpoint of applications, our investigated results have significant potential application on solid state lighting. They could also promote the progress of the LEDs industry in Taiwan.