砷離子佈植半絕緣性砷化鎵之光調制反射光譜研究

Abstract

本文主要探討光調制反射光譜(PR) 技術及其機制.樣品為高劑量砷離 子佈植之砷化鎵晶片,此樣品特性為載子生命期很短,約為1E-12秒.當所用 來調制的雷射光強度所激發的電子電洞對愈多時,發現並不能單純以表面 電場調制的模型解釋,而必須再考慮能隙填隙,能隙縮減和自由載子吸收三 種效應.驗諸半絕緣性砷化鎵基板的PR譜形量測,發現即使是微弱的雷射光 強度,其PR譜形,為表面電場調制和三種效應的疊加.所以若仍僅以傳統表 面電場調制的模型去分析,將會容易造成誤判以及所得的參數不準確. In this work, We study the mechanism of photoreflectance(PR) spectroscopy by probing the high-dosage As-implanted GaAs substrate. The samples have a very short carrier life-time about a pico second. As the concentration of electron-hole pair generated by the pumping laser was great enough, we found that the PR spectrum could not simply analyzed by using the surface electric field modulation model. Instead, bandfilling, band-gap shrinkage, ands free-carrier absorption effects should be taken into accounts. Significance of these three effects is quantitatively analyzed to compare with the experimental data. Semi-insulating GaAs substrates were also characterized by using PR technique with the model including surface electric field modulation and these three effects. The results support our proposed model.