Study Of Low-dimensional Photodectors Based On New Mechanism Of Photodetection

As the nanomaterials preparation and micro/nano fabrication enhance unceasingly, many kinds of novel one- and two-dimensional materials have been widely investigated in the recent decade. The excellent optical and physical properties of low dimensional materials enable high gain, fast response and wide spectrum photodetectors. In this paper, we mainly focus on the study of low-dimensional photodectors based on new mechanism of photodetection, including In As nanowire visible to near-infrared photodector, graphene near-infrared photodector, and Ga N based HEMT for terahertz photodection. Details are as follows: 1. We design core/shell-like In As NWs grown by chemical vapor deposition(CVD), in which a self-assembled “photogating layer”(PGL) is formed near the NW surface. The nanowire back-gated transistors are fabricated by electron beam lithography. The key function of the PGL, under light illumination, is trapping electrons generated from the core and in return the electrons maintaining trapped in the PGL form a strong negative built-in electric field to modulate the core conductance, resulting in an anomalous photocurrent. High photoconductive gain of ~-105 and fast response time 12 ms are obtained in the visible spectral regime at room temperature. Photoconductive gain of ~-1.1 is obtained in the near-infrared spectrum at room temperature. 2. The graphene back-gated transistors are fabricated by using mechanical exfoliation and electron beam lithography. The photocurrents origining from the built-in electric field at the graphene-metal junction and from photothermoelectric effect induced by unintentional p+ doping are obtained by scanning photocurrent microscopy with near-infrared light. In addition, the amplitude of photocurrent can be tuned by changing the back gate voltage to tune the graphene Fermi level. At the last, by deploying the graphene device as a point-like detector in a self-developed laser active imaging system, we obtain the clear infrared imaging for the target sample at room temperature. 3. An alternative-grating gated Al Ga N/Ga N field-effect transistor is proposed by considering the slit regions to be covered by a highly doped semiconductor acting as supplemental gates. The plasmonic resonant absorption spectra are studied at THz frequencies using the FDTD method. The 2DEGs, under supplemental gates, as efficient electric vibrators modulated by a positive voltage, can make the excitation of the higher order plasmon modes under metallic fingers more efficient.