P-contact Photolithography Process Development for GaN-based Devices

• Main Authors: Yao-tsung Hsieh, 謝曜聰
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/27476138620366673149

碩士 === 國立臺灣科技大學 === 光電工程研究所 === 98 === GaN is one of the major materials for fabricating light-emitting diodes (LED). The ternary compound semiconductor InxGa1−xN having a direct band gap from about 0.7eV to 3.4 eV is applicable in the fields of light-emitting diodes and solar cells. Because p-GaN has a larger work function(7.5 eV) than metals (under 6eV), p-GaN metal contact often behaves like Schottky contact that deteriorates the performance of the devices. In order to solve this problem, this study is aiming at fabricating ohmic p-type contacts. Based on the principle of transmission line model, experiments under different annealing gases including N2, O2 and Clean Dry Air (CDA) were performed. I-V curves and specific contact resistances were measured and compared. We obtained the lowest specific contact resistance while using CDA annealing gas, and its IV characteristic is the most near ohmic. As a result, the turn-on voltage of our LED has been significantly reduced. Moreover, in the photolithography process, we observed nonuniform negative photoresist spreading due to large mesa height. That caused incomplete photoresist reversal and lift-off leading to short circuit between p and n electrodes. We adjusted parameters of the photolithography process and eliminated leakage current. As a result, the open-circuit voltage of our solar cell has been increased to 2V.