Study On The Photoconductivity Characteristics Of Integrated Nanowire-chip With Graded Bandgap

Among the semiconductor materials, CdS and CdSe are the most promising new-typeone-dimensional nanostructures in the field of optical detection. But direct bandgapsemiconductor nanowires with a certain bandgap has the maximum response in thewavelength near its bandgap. The problem of lattice mismatch is resolved by thebreakthrough of the synthesis of ternary alloy nanowires, making it possible to realizehigh-sensitivity, wide spectrum detection. In this paper, the CdSSe nanowire-chip wassynthesized and then realized the fabrication of large-size, wide spectrum response, andhigh-sensitivity photodetector. The theory and experimental analysis will promote suchkind of detector based on alloy nanowire-chip to be used in many field that need highsensitivity and large-scale macro-detector. The thesis includes following parts:Aluminum electrodes with200nm thickness were patterned on the surface ofintegrated CdSSe nanowire-chip by thermal evaporation system. The CdSSe nanowire-chipbased photodetector shows excellent properties of photoconductivity characteristics andoptical detection due to the tunable bandgap.(1)With graded bandgap ranges from1.7eV to2.4eV, CdSxSe1-x(x ranges from0to1)nanowires were synthesized on different substrates(muscovite and silicon) usingconditions-controlled chemical vapor deposition (CVD). Compared to chip synthesized onsilicon, the nanowire-chip based on muscovite shows larger light-to-dark ratios as high as106. Thus, muscovite has advantages of insulation, low-cost and easily layered structure,reducing the costs and difficulty of the fabrication for photodetector. Aluminum electrodesof different shapes (interdigital electrodes and strip electrodes) were checked to study theinfluence of electrodes on the photoconductivity characteristics. The carriers density andcollection efficiency of electrons are dominated by electrodes and the photoactive area,respectively. By comparison, electrodes with0.5mm in width and spacing show the bestperformance. The effective thickness is found to have great influence on photoconductivitycharacteristics. The chip with effective thickness of70μm shows the best performance. Theperformance of CdSSe nanowire-chip is dominated by complicated behaviors of traps,carriers scattering, and absorption.(2) The photoconductivity of different nanowire-chip was studied. For the spectral range covering from400nm to700nm, the nanowire-chip exhibits wide uniform spectrumresponsibility. The nanowire-chip detector works well as switched the frequency up to100Hz. The time constant of the response was studied.(3) The temperature dependent photoconductivity characteristics of the photodetectoris studied at low-temperature. With temperature decrease, the darkcurrent shows adownward trend due to thermal noise and carriers scattering reduce, while the photocurrentshows an upward trend. The light-to-dark current ratio increases with the temperaturedecrease, which guarantee the CdSSe nanowire-chip photodetectors with bettercharacteristics at low temperature. It is the first time for such kind of photodetector to showbetter performace at low temperature. In this paper, we offer a new way to fabricatemacro-photodetector by nanostructures. The new-type large-size photodetector with highsensitivity and broad spectrum response can meet many requirements in many fields toreplace the silicon-based detector.