Zero And One-Dimensional Semiconductor Nanostructures Based Nanodevices And Their Applications

Semiconductor nanomaterials are the most potential research areas from last couple of decades because of their electronic and optoelectronic applications.The properties of nanomaterials are entirely different from their bulk because of quantum confinement effects and large surface to volume ratio.In this thesis,different semiconducting nanostructures,such as Zinc Sulfide(ZnS)nanoparticles,Gallium Arsenide(Ga As)nanowires and Zinc Oxide(Zn O)nanobelts have been studies for many applications,like field effect transistor,photodetector,single electron transistor and single electron pump.ZnS nanoparticles(NPs)have been synthesized by chemical co-precipitation technique.Clear morphology and spherical shape of NPs have been confirmed by Scanning Electron Microscopy(SEM)and Transmission electron Microscopy(TEM)with average diameter of 20 nm.DC conductivity analysis to deduce the conduction mechanism and dielectric analysis from impedance spectroscopy to study polarization in ZnS NPs have been studies in temperature range of 300 K to 400 K.Richardson schottky emission has been the prevailing transport mechanism by comparing the theoretical and experimental value of field lowering coefficient.Dielectric analysis reveals that the Maxwell-Wagner-Sillars(MWS)interfacial polarization is responsible for the increase in dielectric permittivity and dielectric loss at lower frequencies.Foreign-catalyzed assisted grown nanowires deteriorate the performance of nanodevices because of incorporation of foreign impurities into the nanowires.Self-catalyzed assisted grown nanowires drastically enhance the features of devices because of twin layers free structure of nanowires having uniform morphology with exclusion of foreign impurities.A thorough study on temperature dependent transport characteristics of field effect transistor based on self-catalyzed grown Ga As single nanowire(NW)has been carried out.The carrier mobility in Ga As field effect transistor at room temperature is 0.05 cm2/V-sec whereas the value at low temperature is 0.0005 cm2/V-sec respectively.The low mobility at room temperature is attributed to surface roughness scattering effects and charge carriers trapping effect by surface states,and low value of mobility is attributed to the reduced thermal activation energy of the charge carriers at low temperature.Optoelectronics devices are also significantly influenced by defects in NWs,such as stacking faults can form carrier-transportation barriers and foreign impurities(Au)with deep-energy levels can form carrier traps and non-radiative recombination centers.Therefore self-catalyzed NWs are best candidate for optoelectronic devices.Photodetector based on self-catalyzed grown p-type Ga As single NW has been fabricated.Due to the absence of stacking faults and suppression of large amount of defects with deep energy levels,the photodetector exhibits room-temperature high photo responsivity of 1.45 x 105 A W-1 and excellent specific detectivity(D*)up to 1.48 x 1014 Jones for low-intensity light signal with a wavelength of 632.8 nm.The defects free structure of Ga As NWs has also been confirmed by photoluminescence spectroscopy.These results demonstrate that these self-catalyzed grown pure-ZB Ga As NWs are the promising candidates for optoelectronics applications.Quantum computing necessitate complete control over the spin of single electron,and diluted magnetic semiconductors(DMSs)have been employed for this purpose but they limit the performance of the devices because of their low Curie temperature,therefore wide bandgap materials operating at room temperature are need of the hour.Single electron transistor based on wide bandgap Zn O single nanobelt(NB)has been fabricated and clear coulomb oscillations are observed at 4.2 K.The periodicity of coulomb diamonds depicts that the coulomb oscillations arise from uniform sized single quantum dots(QDs)while the quasi periodic coulomb diamonds correspond to the contribution from multi-dots present in the NB.The charging energy of electron to the quantum dot has been calculated and its value is about 4 me V and 5 me V in case of single and multi-dot system respectively and the corresponding diameter of QD is about 86 nm and 70 nm.The meticulous single electron pumping in Zn O QD by using single back gated ac signal with varying frequencies has also been observed and the current increase equals exactly to an electron charge times frequency.Accurate single electron pumping make them suitable for single electron spin injection and detection in Zn O nanobelt based devices,which has great potential applications in quantum computing and information technology.