Fabrication And Electroluminescence Of (Mg)ZnO Based MIS Heterostructure Ultraviolet Light Emitting Devices

Wide bandgap (3.37eV) and high exciton binding energy (60meV) make ZnO apromising candidate for ultraviolet (UV) light-emitting diodes (LEDs) and low-thresholdlasing diodes (LDs).However, the difficulty in high quality p-ZnO dopingstill hinders thedevelopment of ZnO homojunction light emitting devices. Therefore, many studies havefocused on the design and development of heterojunction LEDs.As an alternative solution,mental-insulator-semiconductor (MIS) heterojunction devices, which can obtain pure ZnOexcitonic emission by blocking electrons in the active layer, have attracted more and moreattentions. However, for conventional MIS diodes, the electron-hole pairs are generated in theinsulating layer by aso-called “impact-ionization” process under high electric field.Due to therelatively low carrier injection efficiency,the electroluminescence (EL) efficiency of the MISdevice will also be limited. In order to improve the EL efficiency, new p-type semiconductorlayer,serving as the hole-injection layer, was introduced into the ZnO-based MISheterojunction.The primary contents of our work are described as follows:(1) Cuprous oxide (Cu2O) films were prepared via thermal-oxidizing evaporated Cu thinlayers.By optimizing the thermal oxidation conditions,high-quality p-Cu2O thin films can beobtained.Based on this, the Au/Cu2O/MgO/ZnO MIS LEDs were fabricated by inserting thep-Cu2O layer into the conventional Au/MgO/ZnO heterojunctions.I-V curves of the twodevices reveal that injection current was greatly increased after introducing the p-Cu2O layer.What’s more, compared with the conventional Au/MgO/ZnO heterojunction,theAu/Cu2O/MgO/ZnO MIS device shows higher EL intensity at the same injection current.Allthese indicate that the inserted p-Cu2O act as hole-injection layer, facilitate the hole transportto ZnO region, and raise the EL efficiency of the MIS device.(2) To achieve deep-ultraviolet (UV) light emission, MgZnO alloys were employed asthe active layer,and a Au/MgO/MgZnO MIS heterojunction was constructed on the n-Sisubstrate by pulsed laser deposition. The effect of dielectric MgO thickness ondevice’selectrical and EL performance is investigated in detail. The result shows that thedevice performance will be both poor if the MgO thickness is too large or too small. Afteroptimization, a suitable dielectric blocking layer thickness of~60nm was found and arelatively high-efficiency UV EL was also obtained.