Development of light-emitting diodes using well-aligned ZnO nanowire

[[abstract]]Light emitting diode (LED) is considered as the major next-generation luminescence technology, but nowadays insufficient light efficiency of high power LED limits its application for illumination lighting. Some research group have developed nanowrie-inserted LED structure, and the EL intensity shows that the novel LED structure can improve light efficiency effectively. ZnO nanowires grown by hydrothermal method have excellent properties such as single crystal, vertical alignment, broad area growth and simple process. Thus in this study hydrothermal method is adopted to fabricate ZnO nanowires, N-type material of LED is aluminum-doped ZnO film (AZO) deposited by RF sputtering, and P-type materials are ZnO and Mg-doped GaN film. Finally, the characteristics of N-type AZO/ZnO nanowire/P-type ZnO or P-type GaN structure LED will be studied. The ZnO nanowries grown by hydrothermal method are 34 nm-200 nm in diameter, 1 um-2 um in length, and 4 NWs/um2-68.23 NWs/um2 in density. EDS shows the atomic percentage of Zn and O is closed to 50 % : 50 %. XRD peak locates at 34° and shows (002) preferred crystallinity. PL indicates the luminescence peak of nanowries appears at 378 nm, and weak visible emission is observed. HRTEM image shows good crystal structure, and the spacing of lattice fringe is 0.2629 nm. For AZO film, the optimal resistivity is 3×10^(-3) Ω-cm, carrier concentration is 1.72×10^21 cm^(-3) and mobility is 0.0715 cm2/V-s. The average transmittance of visible light is above 80 %, the optimal transmittance at 450 nm is 87 %, and the optimal transmittance at 380 nm is 77 %. ZnO and pure zinc targets are used to deposit P-type ZnO by O2/Ar flow controlling, but unfortunately all fabricated samples still show N-type properties. P2O5-doped ZnO target will be used to fabricated P-type ZnO film continuously. For LED study, ZnO nanowrie/N-type AZO film have been fabricated on Mg-doped P-GaN film (carrier concentration is about 1017 cm-3), the size of LED die is 300 μm × 300 μm. Blue emission is observed from partial area of LED die through long-distance microscope when forward-bias is above 15-20 V, and voltage raise leads to increasing of light intensity. In the next step, current-voltage relation and electroluminescence (EL) spectrum will be examined.