The Studies On Fabrication And Characteristics Of ZnO Based Ultraviolet Emitting Devices Pumped By Electron Beam

Ultraviolet light sources, especially compact ultraviolet laser devices, arecurrently expected to be used in various fields. Practitioners have proposedpromising electron beam pumped (EBP) semiconductor-based light sources. Suchdevices need no p-n junction or electrode contacts, which is the unique advantages ofelectron beam excitation. Therefore, the problems on p-type doping, which has beenblocking the realizing of current pumped light emitting diodes (LEDs) based forwide band gap materials, especially for ZnO, need not be taken into account. Inaddition, the thickness of the active region can be much larger than that in injectionpumped devices, which means higher output power.ZnO is a promising wide bandgap (3.37eV) material with a largeexciton-binding energy (Eb=60meV), which have broad application prospects inultraviolet (UV) LEDs and laser diodes (LD). Aiming at the inadequate of theresearch on EBP portable light source, as well as the blank of the study on EBPZnO-based quantum-well UV light-emitting devices, this dissertation adopted themetal organic chemical vapour deposition and the molecular beam epitaxytechnology to fabricate the EBP ZnO-based UV light-emitting device, and carriedout a number of connected research.Take advantage of refractive index difference between well-layer and barrier layer of quantum-well samples reduced the self-absorption，the large exciton-bindingenergy of ZnO-based semiconductor, and the characteristics of exciton tunneling,optimal acceleration voltage (OAV) of the device was reduced, quantum-confinedstark effect caused by electron accumulation on the sample surface andsuperradiance with a superlinear increase in emission intensity were observed,internal quantum efficiency of ZnO/MgZnO quantum wells was increased; the alloysurface plasmon resonance showed light wavelength selective enhancement. Thesummary of specific content is as follows:1. Cathodoluminescence behavior vs accelerating voltage of electron beam inZnO/MgZnO multi-quantum wells was reported. The samples were grown onsapphire substrate by plasma-assisted molecular beam epitaxy. In a sample withasymmetric double-quantum-wells, a marked reduction of the OVA from7kV to5kV was obtained compared to the symmetrical multi-quantum well sample.Excitontunneling assisted injection is attributed to the main reason of the decrease of OVA.Monte Carlo simulation agrees well with the CL results.A marked red shift of the emission peak was observed clearly under largebeam current excitation, which is attributed to quantum-confined Stark effect causedby electron accumulation on the sample surface.2. We report the cathodoluminescence (CL) property in a ZnO/MgZnOasymmetric double-quantum-well (ADQW) sample compared to that in amulti-quantum-wells (MQWs) sample. Under the same excitation density andacceleration voltage, an18-time enhancement in emission intensity was observed inthe ADQW sample compared to the MQW sample. With increasing the excitationdensity, superlinear increase of emission intensity was observed. Time-resolvedphotoluminescence (TRPL) spectroscopy were used to analysis the exciton tunnelingfrom the narrow well to the wide well. With increasing gradually the excitationdensity, superradiance with a superlinear increase in emission intensity was observed.We report a significant increase in the internal quantum efficiency (IQE) ofZnO/MgZnO multi-quantum wells (MQWs) fabricated on c-plane sapphire substrate by introducing asymmetric double-quantum-well (ADQW) structure. A markedenhancement in efficiency, by as much as1.56times, was observed for a ZnO/MgZnO five-period ADQW grown by plasma-assisted molecular beam epitaxy(P-MBE), that replaced the usual ten-period symmetrical MQWs with asymmetricstructure. The effects of excitons tunnel from the narrow well to the wide well,which proved by photoluminescence spectra and time-resolved photoluminescence(TRPL) spectroscopy, can influence the IQE.3. We design and evaporate silver/aluminum alloy thin film.The alloy surfaceplasmon resonance energy just match MgZnO film peak position which peaked at374nm, which defect emission was shown to be inhibited, and the near band edgeUV radiation was enhanced. The photoluminescence could be150times stronger.We preliminarily proved that energy resonance wavelength of the appropriateproportion of silver/aluminum alloy film with rough surface can be adjusted toapproximately374nm UV wave band, which can influence electron beam pumpedemitting and photoluminescence wavelength selective obviously.