Research On Synthesis And Electrical Properties Of GaN/Si Nanoporous Pillar Array Double Nanoheterostructure

As the most important part of the third generation wide band semiconductor materials, III-V compound semiconductor Gallium Nitride(Ga N) owns a direct wide bandgap(~3.34 e V), high electron mobility(~1000 cm2V-1s-1), and good chemical stability. Therefore it has been widely used in the fields of light emitting diodes(LED), laser diodes(LD), high electron mobility transistor(HEMT), solar cells, and so on. On the other hand, single crystal silicon(Si) is the most important material for the modern electronic industry and information industry, and the silicon planar lithography technology is rather mature. Therefore, there is a great potential in combing Ga N with Si potential for the integration of Ga N devices. With the development of nanotechnology, nano-materials show many novel properties that the bulk materials don’t own. What’s more, when the Ga N and Si are combined to form nano-structures, the problem caused by lattice mismatch and thermal mismatch will be solved. Based on these reasons, silicon nanoporous pillar array(Si-NPA) with micro/nano structures is used as a functional substrate, the Ga N nano-structures were prepared by chemical vapor deposition on Si-NPA. A novel nontraditional, non-planar,multi-interface double nanoheterojunction is formed by the nano-structured Ga N and Si-NPA.The Si-NPA was synthesized by hydrothermal method, then the it was treated by natural oxidation, H2O2 solution oxidation and the dry thermal oxidation at 500℃,and the photoluminescence ability was discussed. The fresh Si-NPA shows a double red light peaks structure, with the oxidation of Si-NPA, a blue light peak appear. So it is confirmed that the blue light peak in the Si-NPA was introduced by the oxide-defects. When the Si-NPA was oxidized at 500℃ by 15 min, the red light peaks was disappeared and the photoluminesence spectrum structure was turned into “one blue peak + one green peak”. In the conditions of natural oxidation and H2O2 solution,he red light peak R1 blue-shifted with the increase of the oxidation time at the beginning, and then red light peak R1 tended to be stable. So, we can confirm that the red light peak in Si-NPA is originated from the quantum confinement effect. There area lot of Si nano-crystal particles in Si-NPA,in the conditions of natural oxidation and H2O2 solution, the diameter of Si nano-crystal particles decreased with the increase of the oxidation time at the beginning leads to the red light peak blue-shift. However, the dry thermal oxidation at 500℃ was more violent than the natural oxidation and H2O2 solution oxidation, so the diameter of Si nano-crystal particles became smaller, so the red light peak blue-shifted to the green region. The light emission of Si-NPA can be effectively tuned by choosing different oxidation methods and oxidation condition.The wurtzite Ga N nano-particles, Ga N naono-wire, and Ga N cone-string structure were grown on Si-NPA substrate by a CVD method using Pt as catalyst.The surface morphology, structure and size of the deposited Ga N could be via through controlling the growth temperature and NH3 flow rate. It was found that the concentration of active nitrogen atoms has a great influence on the microstructure in preparing Ga N by CVD method. With increasing the concentration of active nitrogen atoms, the growth speed of [002] increased. It was found that lower concentration of active nitrogen atoms is beneficial to form of Ga N nano-particles, while higher concentration of active nitrogen atoms is beneficial to the form of Ga N cone-string structure. The photolumenescience results show that the concentration of active nitrogen atoms has no effect on the intrinsic peak, while the yellow light band caused by the defects will blue-shift with the increase of the concentration of active nitrogen atoms. The naostructure of Ga N can be tuned by adjusting the flow rate of NH3 and growth temperature.Through the J-V test. Ga N/Si-NPA double nano-heterojunction had the same rectification effect with the conventional planar heterojunction. when the applied voltage was forward, the current transfer meet the emission model. When the forward voltage was small, the current in the heterojunction is according with Ohm’s law, but with the applied voltage increase to some degree, the current would change with the voltage exponetially. When the heterojunction was applied reverse voltage, the transmission current is accord with the Zener tunneling mechanism, meet the relationshipm-μ-VJ)()(.When the Si-NPA was oxidized, the energy band structure of Ga N/Si-NPA was changed. With increasing the thickness of oxide layer, the barrier height ofheterjunction increases, the carriers need more energy to cross the barrier. When the oxidation time increased to 60 min, the forward current transfer model changed. When the applied voltage is low, the current transfer meets the tunneling mechanism, as the applied voltage increasing, the current transferring was accord with the diffuse model.