Study On Photodetection Mechanism And Application Of CVD-Grown Quasi-One-Dimensional Semiconductor Materials

As a typical representative of low dimensional materials,quasi-one-dimensional materials exhibit some unique electrical and photoelectric properties,so they are widely concerned by researchers in the field of photoelectronic devices such as photodetectors.However,in the growth process of quasi-one-dimensional materials,impurity doping or defects will inevitably be introduced,increasing carrier concentration.The dark current of the device will increase accordingly.Impurities or defects can also affect the response time and the performance of the detector.In this thesis,the growth process and mechanism of quasi-onedimensional semiconductor materials are studied based on the low-cost and efficient chemical vapor deposition(CVD)method.Quasi-one-dimensional cadmium sulfide nanobelts,tellurium nanowires,and nanobelts exhibit excellent and stable properties.The research on photodetectors is carried out around these quasi-one-dimensional semiconductor materials,focusing on the photocurrent generation mechanism of the above photodetectors.By designing unique structures,the dark current and noise of the photodetectors are reduced.Meanwhile,the detectivity,response speed,and other performances of the photodetectors are improved.The application of these photodetectors is also explored.The detailed works are as follows:1.The surface defects of CVD-grown CdS nanobelts were passivated by HfO2,which can reduce the high electron concentration caused by the introduction of unintentional doping in the growth process of materials.The CdS back-gated field-effect transistors were fabricated by micro-nano fabrication technology.The relationship between material defect concentration,material carrier concentration and threshold of transistor device were analyzed.The band regulation model of CdS nanobelts passivated by HfO2 was established and verified by temperature-dependent electrical measurement.The results showed that after HfO2 passivation,the working mode of the device changed from depletion-mode to enhancement-mode,and the dark current of the device decreased obviously at zero gate voltage.At a source-drain voltage of 1 V,the passivated CdS nanobelts phototransistor exhibited an ultrahigh detectivity of 9.07×1014 cm Hz1/2 W-1 at 450 nm.The work demonstrated the passivation method could effectively improve the detectivity of the device.2.The chemical vapor deposition method was used and suitable source material of SnTe2 was selected for the growth of anisotropic low-dimensional tellurium(Te)materials,which could overcome the problems of the large growth rate difference in different crystal directions and difficulty in controlled growth.Quasi-one-dimensional Te nanowires and nanobelts were synthesized,and the growth mechanism of the controlled morphology of Te was studied.The ultra-high hole mobility and broadband polarization detection performance of quasi-one-dimensional Te photodetector were verified.In addition,the Te-based devices owned a blackbody-sensitive infrared detection performance.Specifically,the device showed a high laser responsivity of 6650 AW-1 and a blackbody responsivity of 5.19 A W-1 at 1550 nm.Finally,the high-resolution active imaging based on the Te photodetector was successfully realized.This work confirmed the excellent infrared detection capability of Te in low-dimensional material systems.3.To reduce the dark current and improve the response speed of quasi-one-dimensional Te devices,a heterojunction device based on quasi-one-dimensional Te nanobelts and graphene was constructed.The self-powered infrared detection of the device was realized,thus the dark current and noise of the detector are effectively suppressed.The results showed that the device achieved a high detectivity and a fast response from visible light to mid-infrared.Under 2 μm laser irradiation,the heterojunction photodetector showed a detectivity of 1.04×109 cm Hz1/2 W-1,a fast response time of 28 μs,and good stability.Without bias,the blackbody peak detectivity of the photodetector could reach 3.69×108 cm Hz1/2 W-1.Further studies on the linear array devices showed that the devices exhibited good performance uniformity for potential imaging applications.