Utilizing Different Grating Structures to Investigate the Influence of Evanescent Wave in Quantum Well Infrared Photodetector

量子井光偵測器現時於紅外線波段中廣泛應用中，其中涵括了天文、醫療、建築、軍事、安全系統等領域。如何能最有效且最省能提高其吸收效率遂成為熱門之課題。吾人冀以光柵之系統大幅改善光柵之吸能效率，並著重於了解其蝕刻深度與吸收效率之相關性。並習察得蝕刻至底電極時有較高之響應率，以此為基底，引用原理分析解釋，並做進一步之討論。 光柵者，能使光繞射，藉以使其電場可大量垂直於基板表面，大幅增加光電流之產生。光繞射入光柵溝槽後，將產生表面消逝波，能大幅增加其於主動層處之吸收，並觀察蝕刻深度之深淺，以研究蝕刻深度及響應度之變化。 目前之結果，吾人發現蝕刻至底電極時有較佳響應，但其結果仍有向上空間，分析為應是表面電子復合率高及主動層過多被蝕刻所致。除此之外，吾人亦有探討蝕刻相同深度不同光柵週期時之響應度比較，得其結果為於光柵週期2.0微米時有最高之響應率，並究其原因分析探討之。The quantum-well infrared photodetector(QWIP) is widely applied in contemporary technology. It is mainly applied in the field of astronomy, medical science, architecture, military and safety system. Therefore, it became a popular topic on how to make the fabrication of QWIP costless and simultaneously promote its absorption efficiency. In this paper, we attempt to improve the absorption efficiency of QWIP by applying the grating structure. Also, the relation between the etched depth and absorption efficiency will be observed. Consequently, we learned that when the deeper the active layer is etched, the better responsivity is shown. The grating structure can make the light diffract, meaning that the proportion of the electric field direction vertical to the substrate surface can be raised. By doing so, the photocurrent can be generated faster than the previous condition. While the light is diffracted into the grating slot, the evanescent wave will be generated, which can greatly enhance the absorption at the active layer. As for the present result, we observed the highest responsivity when the active layer is etched thoroughly. Yet there are still rooms for improvement. We deduced that it may be resulted from the higher surface recombination and excessively-etching of the active layer. Besides, we also investigated the responsivity under fixed etched depth and different grating pitch. The result shows that the optimal grating pitch is 2.0 micrometer. The detail reason will be discussed in the 4th chapter