Research On Promoting Luminous Efficiency Of ZnO And ZnO/ZnMgO MQWs Light Emitting Devices

Zinc Oxide(ZnO)has been regarded as a competitive candidate for ultraviolet(UV)optoelectronic devices owing to its excellent photoelectric properties.Currently,however,the prepared ZnO based light emitting device is still faced with such problems as low efficiency,unstability,and failed to meet the application requirements.Improving the luminous performance of ZnO materials and devices to make efficient and stable light-emitting device has been the efforts of this research field.With this as aims,the following 3 parts of work are carried out.1.ZnO,p-type Na-doped ZnO films and Non-polar-oriented ZnO/ZnMgO multiple quantum wells(MQWs)are fabricated by plasma-assisted molecular beam epitaxy(P-MBE).60-fold,10-fold and 20-fold enhancement of band-edge photoluminescence(PL)are obtained by employing Pt nanoparticle,respectively.Moreover,the internal quantum efficiency of MQWs is strongly improved from 1.8%to 12%.Besides surface plasmons coupling,the conversion of non-radiative recombination into UV emission is vital for the enhancement confirmed by low-temperature PL.2.The lack of stable and reliable p-type ZnO still hampers its potential applications.Inefficient hole injection from the p-type layer is one of the essential issues leading to low efficiency device emitting.Based on the band offsets study and film structure properties investigation,we analyse the coordinated and supporting roles of ZnMgBeO to p-type doping and explore a new method to obtain high efficiency stable p-type ZnO material,which lay the foundation to realize high efficiency light-emitting device.ZnMgO/ZnMgBeO heterojunctions with different Mg content and bandgap are fabricated by P-MBE.The band offsets of the heterojunctions have been investigated by using X-ray photoelectron spectroscopy(XPS)measurements.The experimental measurements have offered a strong support that alloying Be in ZnMgO alloys is hopeful to form a higher Valance band maximam and conduction band minimum,which is helpful to enhance the p-type dopability of ZnMgO.First-principles calculations show that the formation energy of oxygen vacancy(Vo)is high with Be incorporation.It reveals that Be can suppress the formation of Vo defects.The suppression of Vo defect-related visible emission and the decrease of background electron concentration of ZnMgO also have been confirmed by PL and Hall measurements.Therefore,we put forward introducing a little Be to play its auxiliary role in p-type doping,and guarantee the quality of film crystal at the same time.3.Usually taking MQWs as active layer is an important step to design high efficiency light emitting devices.In order to avoid the absence of stable and reliable p-type ZnO material,p-GaN is proposed to be used as epitaxial substrate and hole transport layer and p-GaN/(ZnO/ZnMgO)MQWs/n-ZnO device structure is raised and the light emitting device is fabricated.I-V test shows the device has rectification effect.Electroluminescence(EL)emission peaks are at 375 nm and?550 nm,indicating recombination in ZnO well layer.Due to the quantum confinement effect,electrons are confined in MQWs layer without injected into p-type layer.It is hopeful to achieve high efficiency light emitting devices.