Synthesis, Characterization, And Applications Of GaN Nano/Microwires

As a third-generation semiconductor, Galium Ntride(GaN) has been extensively studied due to its superior characteristics, e.g., wide direct band gap, high electron mobility, high thermal conductivity, and high breakdown field. With the miniature developing trend of photoelectric devices, GaN-based micro-nano devices have been attracting highly significant attention on blue/ultraviolet light emission and high-temperature high power electronic devices. To date, there is a lot of devices based on one-dimensional GaN nano/micro materials, including field-effect transistors(FET), optically pumped semiconductor lasers, logic devices and light detectors, were intensively reported. Indeed, the synthesis of high-quality GaN nano/micro materials is the key to fabricate GaN-based micro-nano device, hence the controlled synthesis of one-dimensional GaN micro-nanowires and its arrays is of very importance. In this paper, GaN nano/microwires with different structures and sizes have been synthesized by chemical vapor deposition(CVD) method, and its structural, optical and electrical properties and applications have also been studied.The main achievements are summarized as follows.(1) The CVD synthesis and characterization of GaN nano/microwires.Focusing on the process of CVD systhesis, structural and optical properties characterizations by using a field-emission scanning electron microscope(SEM), a high-resolution transmission electron microscope(TEM), an X-ray diffractometer(XRD) and a Raman spectroscopy, and the growth mechanism.(I) Using Ga2O3 as the Ga source, the GaN nanowires with a diameter of 100~200 nm and length of ~50 μm were grown on Si wafer through a vapor-liquid-solid(VLS) method; the GaN microwires, with hexagonal cross sections and having a diameter of 1~15 μm and length of several hundred micrometers, were grown on a ceramic boat, and GaN microarrays on c-GaN substrate through a vapor-liquid(VS) method.(II) Using high-purity metal Ga as the Ga source, millimeter-long GaN microwires with bamboo-like morphology along the c-axis were synthesized, and the VLS growthGaN nanowires with controlled crystallographic orientations on different planes of sapphire.(2) One dimensional GaN microwires/microarrays optically pumped ultra-violent lasers at room temperature. A single GaN microwire with Fabry-Perot cavities, and GaN microarrays with whispering gallery mode(WGM) cavitie were fabricated, and the excitation properties of optical pumping were studied. We realized the single GaN microwires with WGM excitation and obtained the optical pump laser based on the single mode of small diameter GaN, where laser peak spacing decreases with wire diameter increases. Additionally, GaN micro array laser belongs to Fabry-Perot mode laser, and the excitation threshold is 410 KW/cm2.(3) We firstly reported a multilevel bamboo-like GaN nanowire memristor based on defect boundaries(DBAs), and the characteristics of the GaN memristor can be modulated by the piezotronic effect. Defect boundary areas(DBAs) near the bamboo knots produced apparent switching between high and low resistance states upon sweeping of biased voltages with various magnitudes across the GaN NW-based devices at room temperature. Furthermore, by coupling the piezoelectric and semiconducting properties in the GaN nanowires(NWs), the piezotronic effect was introduced to effectively modulate the SET voltages via strain-induced piezoelectric polarizations created at the DBA interface upon mechanical deformation. The experimental results indicated that the device remembered the most recent resistance states when the power was turned off, and the waveform was tunable via the delayed switching effect.The works in the paper has provided cheap raw materials and synthesis methods for GaN-based micro-nano devices fabrication, and an alternative approach to design memristors based on nanostructured piezoelectric semiconductors using the piezotronic effect, which introduces GaN nano/micro materials in very important potential applications for biological sciences, environmental monitoring, defense technology and personal electronics.