Recently, surface plasmon (SP)-exciton coupling has been wildly applied in nitride semiconductors in order to improve the spontaneous radiative recombination rate [1-3]. However, most works have been focused on the emission enhancement in InGaN-based blue or green light emitting diodes (LEDs). Practically, it is significantly important to improve the emission efficiency in deep-UV AlGaN-base quantum well (QW) structure due to its intrinsically low internal quantum efficiency (IQE) induced by the high defect density in its epitaxy layer . But, the effective SP-exciton coupling with matched energy in deep-UV region is still a challenge issue due to the lack of appropriate metal structures and compatible fabrication techniques.
In this work, the Al nanoparticles (NPs) were introduced by the nanosphere lithography (NSL) and deposition techniques into the AlGaN based MQWs with optimized size and structure. Due to the local surface plasmon (LSP) coupling with the excitons in QWs, emission enhancement in deep UV region has been achieved in the Al NPs decorated AlGaN MQWs structure with comparison to the bare MQWs. Theoretical calculations on the energy subbands of AlGaN QWs were further carried out to investigate the corresponding mechanisms, in which the hot carrier transition activated by SP-exciton coupling was believed to be mainly responsible for the enhancement. This work demonstrated a low cost, wafer scale fabrication process, which can be potentially employed to the practical SP-enhanced AlGaN-based deep UV LEDs with high IQEs.
ZnO thin films with or without Al doping were grown on the glass substrates by sol-gel method and subsequently
annealing treatments at high temperatures were performed to optimize films' morphologies and properties. The crystal
structures of ZnO films were characterized by X-ray diffraction (XRD), and XRD spectra show a shift of (002)
diffraction peak to the higher 2θ values with changing the Al-doping concentration. Optical transmittance spectrums
exhibit a sharp absorption edge at around 380nm undergoing a blue shift induced by aluminum doping. An apparent
particle size decreasing was displayed by scanning electron microscopy (SEM) images with the Al-doping concentration
The Al-doped ZnO (AZO) films were deposited on glass by RF magnetron sputtering under different sputtering power:
75W, 120W, 160W and 200W. During the films deposition, the other sputtering conditions were maintained constant.
The crystal structures of the AZO films were characterized and analyzed by X-ray diffraction. The surface morphologies
of the films were observed by SEM. The transmission spectra of the films were measured using a spectrophotometer
within the range from 200 to 800 nm at room temperature. The results indicate each of the films has a preferential c-axis
orientation and the grain size increases with the increase of sputtering power. All the films exhibit a high transmittance in
visible region and have sharp ultraviolet absorption characteristics.
ZnO films, with C-axis preferred orientation, were deposited on SiO2/n- Si by radio frequency (RF) magnetron sputtering. The interdigital metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors were fabricated by using Ag as Schottky contact metal. For comparison, ZnO Schottky diodes were also fabricated by using Ag-ZnO-Al structures. Aluminum was used to form Ohmic contacts. Current voltage (I-V) characteristics of these devices have been analyzed. The Schottky diodes exhibit distinct rectifying I-V characteristics. The barrier height of the Ag/ZnO Schottky contacts is around 0.65 eV. The leakage current for MSM photodetector is less than 6 x 10<sup>-7</sup>A at a bias of 5V. The photoresponsivity of MSM photodetector is much higher in the ultraviolet range than in the visible range. The UV/visible (350nm/500nm) rejection ratio is more than one order of magnitude. The photoresponsivity of MSM detector exhibits a maximum value around 370 nm.
ZnO films have been deposited on SiO2/Si substrates by rf magnetron sputtering. The rms roughness of the sample's surface was surveyed by using an atomic force microscope, and is less than 10 nm. The theoretical reflectance of the air/film/middle layer/substrate structure has been deduced. In the light of this theoretical reflectance, the complex refractive index ñ()=n()+ik() of the sample below the interband absorption edge has been fitted with a Lorentz oscillator model. The absorption coefficient () of the sample is reported, and the result shows the sample has weak absorption around 490 nm.
ZnO nano films were deposited on SiO<sub>2</sub>/P-Si (100) by RF magnetron sputtering. The interrelationships among growth conditions, crystal structures, and optical properties of the ZnO films were discussed. The reflection spectra of the films reveal that the band-gap of the films is between 3.2-3.3eV. The photoluminescence spectra provide further evidence for the relation between the green emission of ZnO films and the oxygen vacancy or Zn interstitial related defects. The results also demonstrate that the UV emission of ZnO is dependent on the size of the nano-crystallites forming the films. By comparing with the photoluminescence spectra at low temperature, the possible mechanism for this dependent relation was discussed.
The vanadium oxide thin films were prepared by R.F. magnetron sputtering method under different deposition conditions. The microstructures of the samples have been investigated by XRD, XPS, and the Laser Scanning Confocal Microscope . By XRD and XPS, it was found that properly decreasing substrate temperature or increasing sputtering power, larger crystalline particle size and better crystalline orientation with V<sub>2</sub>O<sub>5</sub> (001) after annealing can be gotten; Properly increasing substrate temperature or reducing sputtering power, the proportions of high valence vanadium oxides are increased. Based on our analyses, high-purity vanadium pentoxide films have been prepared by adjusting flux ratio of O<sub>2</sub> and Ar, substrate temperature, and sputtering power.