Research On Field Coupling Mechanism And Structure Of Field-effect Terahertz Self-mixing Detectors

Terahertz frequency range is a region of electromagnetic spectrum between in-frared wave and millimeter wave,and offers specificities of optics and microwave elec-tronics.Terahertz technologies have a broad application prospect in many fields such as radar,communication,non-destructive detection,biomedical and environmental de-tection.The research on terahertz source and terahertz detector are two key factors influencing the development of terahertz technology.Due to the weak radiation power of terahertz source at present,the sensitivity of terahertz detectors is particularly impor-tant.Especially,the improvement of the sensitivity of the detector at room temperature is of great significance to promote the application of terahertz technology.Based on the theoretical self-mixing detecting model,we improve the optical and electrical sensitivity of the terahertz detector by optimizing the integrated terahertz an-tenna and improving the efficiency of optical coupling,to optimize the design and the performance of AlGaN/GaN high electron mobility transistor(HEMT_terahertz detec-tors.The detection of the incoherent terahertz radiation and the local electric field could verify the correctness of the self-mixing model.The main contents and the main results of this thesis are as follows:1.Introducing the model of terahertz self-mixing detecting and the effect of ter-ahertz antenna parameters on the sensitivity of the detector.Based on the quasi-static model,we illuminate the terahertz self-mixing model of AlGaN/GaN HEMT detec-tors,in the two main means:direct detection and heterodyne detection.We analyse the effect of the terahertz antenna on the responsitivity of the detectors and how each parameter of the antenna affect the responsitivity.The length and the width of the ter-ahertz antenna determine the response frequency of the detector,the distance between the antenna influences the intensity of induced mixing electric field in channel,and the length of the gate controls the strength of the channel transconductance.After improv-ing these parameters,the sensitivity of the detector at room temperature raises an order of magnitude and the noise equivalent power at room temperature is reduced to less than 10 pW/Hz0-5.2.Extending the detection frequency range of the detector to 0.1-1 THz.Because of its limited response bandwidth,the terahertz antenna can only detect the teahertz radiation within a little terahertz range.We improve the current terahertz antenna by finite-different time-domain method,and design the special size of terahertz antenna for different detecting frequency.The detecting frequency range of the combined terahertz detector is extended to 0.1-1 THz.3.Assembling the terahertz detector with the silicon lens or horn waveguide an-tenna.We simulate the transmission characteristics and electric field distribution char-acteristics of the terahertz waves inside the silicon lens or horn waveguide antenna,optimize the thickness of the silicon lens,and integrate the terahertz detector with the silicon lens or horn waveguide antenna to form detector assembly.Because of the con-vergence properties of silicon lens and diagonal horn antenna for terahertz waves,the effective availability of the detector to the incident radiation improves,and the noise equivalent power of the detector is 30 times smaller than that of the pure detectors.The interference effect caused by the substrate thickness could also be eliminated.Besides,we package the terahertz detector chip in metal shell to form the detector module by in-tegrating the detector chip with silicon lens and the amplifier circuit.The photoresponse of the module could be read directly wothout another external amplification.And the module is compact and portable,easy to use.4.Representating the local electric field of the terahertz self-mixing detector.De-tecting the local response by converging the incident terahertz waves after the hyper-hemispherical silicon lens and controlling the 2DEG in the channel with sourve/drain voltage.This experimental result agrees well with the simulated distribution charac-teristics of terahertz electric fields on both sides of the gate,and verifies directly the theoretical model.And at the same time,the deficiency of the current detector structure that the photocurrent phase inverts probably when the incident terahertz wave irradi-ates part of the detector is revealed,which provides the basis for subsequent detector structure optimization.5.Detecting the incoherent terahertz wave by the field-effect mixing terahertz de-tector,proving that the terahertz detector based on self-mixing model in HEMT can de-tect both coherent continuous terahertz wave and incoherent broadband terahertz wave.By using the field-effect terahertz detectors with response frequency range around 0.34 THz,0.65 THz and 0.9 THz,respectively,the detection and imaging experiment of incoherent terahertz radiation of 900 K blackbody could be realized at liquid nitrogen temperature.This thesis analyses the model of the field-effect self-mixing detecting,and the ef-fect of the terahertz antenna on the photoresponse,and hance improves the sensitivity of the detector specifically.The terahertz detector could detect the coherent and inco-herent broadband terahertz wave.With integrating with silicon lens or horn waveguide antenna,the noise equivalent power of the detector at room temperature could be op-timized to 10 pW/Hz0.5.Simultaneously the terahertz self-mixing model is vertified,and the structural defect is revealed with incident local electric field,which could be as the basis for the subsequent optimization.