Research On The Synthesis And Optical, Electronic, And Thermal Properties Of Several Ⅲ-Ⅴ Semiconductor Nanowires

In recent years, Ⅲ-Ⅴsemicondctor nanowires have attracted extensive attentionduo to their high electron mobility and large excition Bohr radii. At present,metal-organic chemical vapor deposition (MOCVD) and molecular-beam epitaxy(MBE) are the major methods to synthesize Ⅲ-Ⅴ nanowires. However, the high costand the extremely toxicity of conventional group V precursors (for example, arsineand phos-phine) restrain the generalization and application of the method. In thisdissertation, several Ⅲ-Ⅴ semicondctor nanowires, including InP, InAs, GaSbnanowires, composition completely tunable InAsxP1-xalloy nanowires, andcomposition partially tunable InGaAsSb alloy nanowires have been grown via aconventional chemical vapor deposition (CVD) method. The morphology,composition, and structure of the products were characterized by scanning electronmicroscope (SEM), X-ray diffraction (XRD), and scanning transmission electronmicroscopy (STEM). The photoluminescence (PL) of the samples were exploredthrough scanning near-field optical microscope (SNOM) and a home-built infrared PLsetup. The behavior of transistors based on InP and InAs nanowires were investigatedusing semiconductor parameter analyzer. The photoelectric response characteristic ofInAsxP1-xnanowires was investigated by semiconductor parameter analyzer combinedwith femto-second laser. Furthermore, the thermal conductivities of the InAsnanowires with different diameter were measured via a laser heating. The main novelpoints are shown as follows：1. The InP nanowires with good good crystallinity were synthesized by simpleCVD method combined with vapor–liquid–solid (VLS) mechanism.Temperature-dependent photoluminescence showed that the emission peak graduallychanged from790nm to826nm with the increase of temperature from77K to300K.The transistor based on a single nanowire presented high on/off current ratio andelectron mobility. Next, by changing deposition mode, we synthesized the pearl-likeInP nanowires and quantum dots (QDs) complex structure. Raman spectrum showedthat a surface phonon (SP) mode located near the longitudinal optical (LO) mode ofInP nanowires. This is the first time that SP mode was observed in the samplesynthesized by CVD method. Room-temperature photoluminescence showed that thecomplex structure simultaneously exhibited PL emission of InP quantum dots and nanowires. Compared with the PL of InP bulk, both emission peaks have significantblue shift, which was attributed to the quantum confinement effects. At the same time,because of the broad size distribution of the QDs, the PL peak of InP QDs had verybroad emission linewidth.2. InAs nanowires were grown by a conventional CVD method. A lot of experimentsfound that the nanowires mainly deposited in the temperature ranging from400℃-460℃，and corresponding diameters gradually increased from100nm to190nm. The structurecharacterization results indicated that the sample had good crystal structure. The transistorconstructed with the single InAs nanowire had high on/off current ratio and electronmobility. In addition, a simple and low cost laser heating method was used to measure thethermal conductivities of nanowires with different diameters. It’s found that thethermal conductivities present monotonic decrease with decreasing diameters, whichis ascribed to the mean free path reduction of phonon for the enhancedphonon-boundary scattering.3. Composition and bandgap completely tunable InAsxP1-xnanowires (NWs) weresynthesized by vapor-liquid-solid (VLS) mechanism combining with an in situion-exchange (IE) process. Photoluminescence spectra showed that these alloynanowires exhibited composition-dependent infrared emission, with the peakwavelength continuously varying from860nm to3070nm. In addition, theseInAsxP1-xNWs exhibited different photocurrent response peaks， with the Ascomposition (x) increasing from0to1, the photocurrent response peak was graduallyredshift from900nm to2900nm, which was ascribed to the highly efficientgeneration of electron-hole inducing by band-to-band absorption. At the same time,it’s found that there are much wider Urbach tail in the ternary alloy than InP and InAs.The wide Urbach tails reduce the recombination rate of the photo-generated carrier, sothe alloy InAsxP1-xnanowires showed higher responsivity and external quantumefficiency than InP and InAs.4. GaSb nanowires with well-crystallized phases have been grown by CVDmethod. Temperature-dependent PL showed the PL peak redshift from1640nm to1710nm with the temperature increasing from77K to300K. In addition, thecomposition partially tunable InGaAsSb alloy nanowires were synthesized. Along thegrowth direction of nanowires, the content of As increased gradually and the contentof Ga decreased. Compared with the PL peak of GaSb at77K, the PL peak of thegraded nanowire showed redshift and significant broadening.