The design of double-modulation photoreflectance measurement system

• Main Authors: Ying-Jui Chen, 陳盈瑞
• Other Authors: Ying-Sheng Huang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/08231509685851366501

碩士 === 國立臺灣科技大學 === 電子工程系 === 89 === Photoreflectance (PR) is a powerful, contactless, and nondestructive technique capable of probing interband electronic transitions and built-in electric-fields at the surface and in the interface regions in semiconductor materials. It has been widely used as a characterization tool. However, its application to highly luminescent structures and samples with poor surface morphology has been limited because of the difficulty in minimizing the interference from the photoluminescence (PL) and the pump beam that is scattered from the surface. We report a new way of making photoreflectance measurements to overcome the above-mentioned problems. A double-modulation PR is presented, where both the probe and pump beams are modulated. The configuration enables isolation of the PR signals from the PL and scattered pump beam signals through detection at the sum frequency. A careful choice of frequencies and specially designed filters and tuned amplifiers were needed to achieve optimum operation. A complete system along with the necessary circuits is presented and applied to InGaP2 bulk materials, which has a highly luminescent quantum-well (QW) laser structure and ReS2 single crystal with poor surface morphology. The results demonstrate the intended capability of the system.