Semiconductor nanowires have shown promising results for next generation integrated electronics such as field effect transistors (FET), tunable optoelectronics and quantum information technology, etc. By reducing device size, the effects of defect states can be readily occurred: such as space charge limited current and hopping transport. Also, the interface property is a significant factor in nanoelectronic device design. In order to solve these problems, a comprehensive investigation of electrical and optical properties becomes extremely important.
Here, charge transport mechanisms are investigated in Se-doped InP nanowires grown via pulsed laser deposition (PLD). Current-voltage (I-V) curves reveal that transport is limited by trapped space charge at high bias rather than Schottky diode behavior in most temperature regimes while at low bias electron mobility calculations indicate that hopping between defect states plays a dominant role. This model is further supported by careful temperature-dependent studies of the zero-bias resistance that reveal a crossover between hopping mechanisms at a temperature of ~ 158 K. Nearest neighbor hopping (NNH) dominates in the high temperature regime (T > 158 K) where resistance is found to depend on exp(T0/T)1.03 and Efros-Shklovskii variable range hopping (ES-VRH) dominates in the low temperature regime (T < 158 K) where resistance is found to depend on exp(TES/T)0.49. The average separation between carriers is comparable to the thermal deBroglie wavelength at all temperatures. As a result, this system is in the quantum regime while both NNH and ES-VRH treat electron-electron interactions classically. When applying a positive gate voltage, the crossover temperature is found to decrease from 158 K to 130 K and the exponent for low temperature regime deviates from the theoretically predicted value, ½. These results highlight the increased importance of defect states in quasi-1D systems and the gate dependence of the crossover temperature, as well as of the related hopping parameters, suggests that applying a gate voltage can tune the strength of electron correlations in these systems.
To explore 1D structures further, superlattice nanowire pattern transfer (SNAP) has been developed where the device design is applicable for the non-local spin transport measurement. In order to obtain injection of spin information from a ferromagnetic to a semiconductor, understanding of interface characteristics is crucial. Here we developed a procedure to improve interface characteristic, thereby enhancing spin injection efficiency. Anisotropic magneto-resistance (AMR) measurements are conducted to determine the coercive fields of ferromagnetic electrodes. Doping concentration, oxide barrier thickness and other parameters can be adjusted further to obtain successful non-local spin transport.