By Jiandong Sun
A accomplished gadget version contemplating either spatial distributions of the terahertz box and the field-effect self-mixing issue has been developed for the 1st time within the thesis. the writer has came upon that it's the strongly localized terahertz box caused in a small fraction of the gated electron channel that performs an enormous function within the excessive responsivity. An AlGaN/GaN-based high-electron-mobility transistor with a 2-micron-sized gate and built-in dipole antennas has been constructed and will provide a noise-equivalent energy as little as forty pW/Hz1/2 at 900 GHz. via extra decreasing the gate size all the way down to 0.2 micron, a noise-equivalent strength of 6 pW/Hz1/2 has been completed. This thesis offers specific experimental innovations and machine simulation for revealing the self-mixing mechanism together with a scanning probe approach for comparing the effectiveness of terahertz antennas. As such, the thesis might be served as a beneficial advent in the direction of extra improvement of high-sensitivity field-effect terahertz detectors for sensible applications.
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Extra info for Field-effect Self-mixing Terahertz Detectors
The total current through the electron channel can be expressed as Ids = 1 L L ix dx = − 0 eW μCg L Vds Vgeff dVx . 22) ⎪ ⎪ ⎩ (Vg − Vth ) 1 − (1 − x/LSR )1/2 , x = [0, LSR ] if Vds > Vg − Vth , where, parameter λ describes the degree of the effective channel-length modulation L → LSR = L/[1 + λ(Vds − Vg + Vth )/(Vg − Vth )2 ] in regime SR, and LLR = L(Vg − Vth )2 /[2(Vg − Vth )Vds − Vds2 ] in regime LR. From Eqs. 22), the charge density and its derivative dnx /dVgeff defined as field-effect factor at any location can be numerically calculated.
By characterization, we not only obtain the I − V characteristics, the responsivity, the noise-equivalent power, the response spectrum, the response speed, the polarization effect, etc, but also we probe the localized self-mixing photocurrent based on which the quasi-static detector model and the design of asymmetric antenna are verified. Under the guidance of the detector model, we focus on the design of terahertz antennas and field-effect gate to improve the detector responsivity and sensitivity.
First, we briefly introduce the AlGaN/GaN heterojunction and their advantages. We introduce the typical structure and basic characteristics of the AlGaN/GaN HEMTs. We also introduce the fabrication process of the terahertz detectors in details. Then, we study AlGaN/GaN detectors without and with source–drain bias. We focus on the basic properties of the detectors, including the responsivity, N E P, response speed, response frequency, and polarization. Finally, we give the comparison of a series of detectors with different terahertz antennas.