Synthesis And Photoelectirc Properties Of P-type Chalcogenide Semiconductor Nanostructures

This dissertation aims to synthesize one-dimensional (1D) nanostructure of p-typechalcogenide compounds,and the electronic properties are investigate. The method which is simpleand controllable is realized to synthesize the1D nanostructures with a specific properties, and thenanoelectronics and nanooptoelectronics are fabricated. However, most of the chalcogenidesemiconductors usually show n-type conductivity and p-type doping is hard to realize because of thestrong self-compensation effects. To realize the practical applications of semiconductornanostructures based on the homojunction and heterjunction, the p-type semiconductors are also anessential issue that must addressed to achieve the rational control of their electrical andphotoelectrical properties. The research results reveal that the n-type conductivity is caused by theanion vacany in the single crystal nanostructure of chalcogenide semiconductors, moreover, thecation vacany will lead to p-type conductivity. So a series of the one-dinensional chalcogenidenanostructures are synthesized by using doping and anion atmosphere compensating techniqueaccording to the fundamental theory of thermodynamics and dynamics, respectively. Thenano-devices are fabricated based on individual1D nanostructure, and the electric and photoelectricproperties are explored. The defect reaction mechanism is proposed to explain the p-typeconductivity. The as-synthesized1D nanostructures with enhanced p-type conductivity may haveimportant potential applications in nanoelectronic and photoelectronic devices. The reaearch resultsare as follows: 1. The intrinsic ZnTe nanoribbons (NRs) are synthesized via a simple thermal evaporationprocess. The characterizations reveal that the NRs have a zinc blende structure with a wideth of300nm and thickness up to30nm and length more than20μm. The nano-field-effect transistors(nano-FET) are fabricated based on single ZnTe NR, and the electrical measurements are carried out.The results reveal that the as-synthesized ZnTe NRs have p-type conductivity which is attributed tothe Zn vacancy in the NR. To enhance the p-type conductivity of the ZnTe NRs, the N-doping ZnTeNRs are synthesized by using NH3as the gaseous dopant source. A series of samples are synthesizedwith different NH3concentrations up to50%. The measurements demonstrate that the controllableN-doped method can effectively improve p-type conductivities yielding a resistivity (ρ) of1.4×10^-1cm, a carrier concentration (nh) of3.6×10¹⁹cm^-3, and a mobility (μh) of1.2cm²V^-1S^-1. It is stronglybelieved that the as-prepared p-type ZnTe NRs with excellent electrical properties are promisingbuilding blocks for the future nanodevices, such as field-effect nanotransistors, electro-opticdetectors, and solar cells.2. Resonant tunneling is firstly found in twin p-type ZnTe nanowire field-effect transistors. Thetwin ZnTe nanowries are synthesized via the thermal evaporation process. X-ray diffraction andhigh-resolution transmission electron microscopy characterization indicate that the as-grown twinnanowire has a zinc-blende crystal structure with an integrated growth direction of [11^-1]. The twinplane is (11^-1) and the angle between the mirror symmetrical planes is1410. The formation of twinsis attributed to the surface tension from the eutectic liquid droplet. Field-effect transistors based onsingle ZnTe twin nanowrie are constructed, the corresponding electrical measurements demonstratethat the twin nanowries have p-type conductivity with a mobility (μh) of0.11cm²V^-1S^-1, and acarrier concentration (n17h) of1.1×10cm^-3. Significantly, the negative differential resistance with apeak-to-valley current ratio of about1.3is observed in p-type twin ZnTe nanowrie field-effecttransistors at room temperature. The periodic barriers produced in the periodic twin interfaces canform multi-barrier and multi-well along one-dimensional direction, and the multi-barrier can bemodulated under external electrical field. When the resonant condition is met, the space charge willbe enhanced with the inherent feedback mechanism, and the resonant tunneling will occur. 3. ZnCdTe semiconductors which possess incomparable properties including high atomicnumber (Z), a large enough band gap and low leakage current, high purity and homogeneous,defect-free materials with acceptable cross-sectional areas and thickness, high intrinsic μτ producthave been extensively used in nuclear medicine, spectrometry, industrial process monitoring,environmental safety and remediation, and basic Physics. The Zn_0.75Cd_0.25Te and Zn_0.3Cd_0.7Tesingle-crystalline NRs are synthesized by a two-step process, the morphology and structurecharacterization demonstrate that the ZnCdTe NRs have a zinc blende structure. The electronictransmission characteristics of the single Zn_0.75Cd_0.25Te and Zn_0.3Cd_0.7Te NR FETs reveal that theNRs have p-type conductivity with mobility (μh) of4.2cm²V^-1S^-1, concentration (nh) of2.7×1015cm^-3, and mobility (μh) of5.7cm²V^-1S^-1, concentration (nh) of1.1×1017cm^-3, respectively. Thep-type conductivity is attributed to Zn and Cd vacancies due to the self-compensation effect. TheX-ray detection characteristics based on the ZnCdTe single-crystalline NR are carried out at thevoltage of2V. The nanodetector shows a high X-ray sensitivity, and short response time less than1S at room temperature in air. The radiation-to-dark current ratio about two orders of magnitude isachieved in the detecting measurement which is high enough for X-ray detecting. The high X-rayirradiation sensitivity and fast X-ray response speed are attributed to the high-aspect-ratio and nearlyperfect single-crystalline quality which cause the reduction of recombination barrier in the onedimensional nanostructures. The X-ray nanodetector based on ZnCdTe NR present significantprofile with lower energy consumption, nano scale and high efficiency, which will develop itsapplications in the promising X-ray detection.4. The phosphorus-doped p-type ZnSe NWs were synthesized by adopting the seleniumatmosphere compensating technique. The morphology and structure characterizations reveal that theZnSe nanowires have a diameter of about160nm and wurtzite structure. The nano-FETs based onsingle ZnSe NW are fabricated, and the electrical measurements are carried out. The results showthat the as-synthesized ZnSe NWs have p-type conductivity with a high mobility (μh) of1.25cm²V^-1S^-1and concentration (nh) of1.47×10¹⁸cm^-3, which demonstrate that the selenium atmospherecompensation technique assisted with phosphorus-doping leads to a substantial action in p-typeconductivity of ZnSe nanowires. The photoluminescence spectrum reveals that the free exciton has energy of2.8eV, and the exciton binding energy is estimated to be13meV. The as-synthesizedZnSe NWs with the significant p-type conductivity may have important potential applications innanoelectronic and optoelectronic devices.5. The p-type Zn_0.7Cd_0.3Se NWs were synthesized by adopting the selenium atmospherecompensating technique. The morphology and structure characterizations reveal that the ZnSenanowires have wurtzite structure with a diameter of200nm, length more than20μm and thegrowth direction of [11^-1]. The nano-FET based on single Zn_0.7Cd_0.3Se NW are fabricated, and theelectrical measurements are carried out, the results demonstrate that the Zn_0.7Cd_0.3Se NWs havep-type conductivity with a high mobility (μh) of12.8cm²V^-1S^-1and concentration (nh) of1.0×1017cm^-3, which demonstrate that the selenium atmosphere compensation technique leads to a substantialaction in p-type conductivity of Zn_0.7Cd_0.3Se nanowires. The as-synthesized Zn_0.7Cd_0.3Se NWs withthe significant p-type conductivity may have important potential applications in nanoelectronic andoptoelectronic devices.