Candidate: Yue Zhuo
Title: Development of Terahertz Quantum Well Photodetector at 3THz'
Date: March 14, 2019
Place: EIT 3142
Supervisor(s): Ban, Dayan
Optoelectronic devices in terahertz region have attracted much attentions thanks to their potential applications in security, spectroscopy, imaging and wireless communications. Even though terahertz technology has long been investigated, detecting terahertz wave is still quite challenging. There has been a large variety of terahertz detectors demonstrated; however, they suffers the drawbacks of slow response and low sensitivity. Among all the terahertz detectors, terahertz quantum well photodetector (THz QWP), benefiting from mature growth techniques by using molecular beam epitaxy (MBE), has proved its fast optical response speed and remarkable sensitivity. Furthermore, THz QWP working at 3THz can be combined with strong terahertz emitter, such as terahertz quantum cascade laser (THz QCL), for ultrafast spectroscopy and imaging applications. Recently, THz QWPs integrated with different grating couplers have been explored and are now intensively investigated improve device temperature performance.
In that regard, we aim to improve the simulation model and develop a new THz QWP absorbing at 3THz. Moreover, numerical COMSOL models are built to analyze optical properties of traditional diffraction metal grating coupler and novel patch antenna coupler in this work. To evaluate device performance, current density-voltage (j-V) profiles were measured inside a close cycle cryostat cooling system. From j-V profiles, device background limited infrared performance (BLIP) temperature was extracted. Absorption spectrum was measured by means of Fourier Transform Infrared spectroscopy (FTIR) with device at 7.7K. Photocurrent measurements was carried out using a lock-in amplifier together with an optical chopper to eliminate the noise level. Having j-V profiles, absorption spectrum and photocurrent measured, detector’s figures of merit, including responsivity and detectivity, were then extracted and calibrated. Results show a peak responsivity of 1.9A/W, peak detectivity of 4.63×1010 cmHz1/2/W and an absorption range from 94.5cm-1 (2.83THz) to 142.7cm-1 (4.25THz). Measured j-V profiles were also compared with simulation results for model verification. In addition, 1D metal grating coupler and patch antenna coupler are investigated and their numerical solutions are compared with literatures for the sake of future research.
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