The study of normal incidence on Quantum Well Infrared Photodetector
Date Issued
2008
Date
2008
Author(s)
Huang, Chun-Ying
Abstract
Due to the limit of intersubband transition selection rule, only the light polarized in the growth direction can cause intersubband transition. However, when doing the research of normal incidence, we found that the edge coupling provided a large part response, which came from TM incident light in Brewster’s angle. Therefore, we design a device(deep channel device) which enlarge the edge and successfully increase the responsivity two to three times of the traditional 45 facet device. By doing a series of experiment, we want to prove that the possibilities of the place light goes into the active layer. Theoretically, the structure with extreme asymmetry in length and width has different responsivity for different polarized light. First, we design a strip mesa to explore the responsivity of different polarized light, and we found that the difference of responsivity between different polarization is smaller than 2%.In the meantime, we interfere the edge of mesa by coating photoresistance to understand if there is any relation between the edge and the leakage of light, and the experimental reveals that device coated photoresistance on the edge has better responsivity than the device without coated photoresistance one to two times. The edge is important source of leakage of light. In addition, we have done some experiment, and prove that penetration of metal and cross-talk between mesas is not true. The responsivity of sample covered by metal is zero, and the difference of resposivity of cross-talk is smaller than 3%. And then, we want to understand whether there is light coupled by mesa array. So we conduct “ The measurement of changeable degree” ：observing the scattering signal through the mesa array in different direction(degree 0 to 90),and we found that the responsivity of sample with structure is larger than sample without structure 0.2.The structure indeed can couple oblique light. At least, the step between metal and the margin of mesa also can be the place of leakage of light. We changed the width of the margin of the metal and mesa from 40μm to 210μm, and found that the responsivity increased with the expansion of width and finally reached the saturation. Therefore, in our opinion, the width of the margin of the metal and mesa has relation to the responsivity. In this paper, we have successful qualitative confirmation of the possible sources of the leakage— the edge and the area of the margin of the metal and mesa. It is an important beginning for us to quantatively optimize the structure of normal incidence.
Subjects
intersubband transition selection rule
QWIP
TM mode
Brewster’s angle
cross-talk
Type
thesis
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