The Preparation and Investigation of ZnO:Al Films and ZnO Based Light-emitting Device
|School||Dalian University of Technology|
|Keywords||Magnetron sputtering Ultrasonic spray pyrolysis Pulsed laser deposition H2 -doped AZO thin films ZnO light-emitting the Device Deep level defects electroluminescence|
ZnO has recently become a very popular material due to its great potential foroptoelectronics applications. The large direct band gap of 3.3 eV, along with the large excitonbinding energy （60 meV） and many other advantages, make ZnO a strong candidate for thenext generation of ultraviolet light emitting and lasing devices operating at high temperaturesand in harsh environments. In this thesis, the Al-doped ZnO （AZO） films were prepared byreactive frequency magnetron sputtering in H2 ambient, and the influence of H2 flux on thetransparent and conductive properties of the AZO films was investingated. Moreover, ZnOhomojunction light-emitting diode was grown on single-crystal GaAs （100） substrate byultrasonic spray pyrolysis （USP） based on the success of N-In codoped p-type ZnO films.Furthermore, As-doped p-type ZnO films were prepared by pulsed laser deposition （PLD）,and the ZnO based devices were fabricated and characterized. The details are as follows:（1） To investigate the influence H2 on the properties of AZO films, the AZO films weregrown on glass substrate by magnetron sputtering with AZO （98 wt.% ZnO 2 wt.% Al2O3）ceramic target in H2 ambient. The resistivity of 4.15×10-4Ω.cm and the average transmittanceof more than 93% in the visible range were obtained with the optimal H2-flux of 1.0 sccm at arelatively lower temperature of 100℃. The method of further improving the electricalproperties of AZO films prepared at low growth temperature can be especially useful forsome low-melting point photoelectric devices and substrates.（2） N-In codoped p-type ZnO films were successfully prepared by ultrasonic spraypyrolysis using CH3COONH4 and In（NO3）3 as the doped source of nitrogen and indium.Based on the achievement of p-type ZnO films, ZnO homojunction light-emitting devicescomprised of N-In codoped p-type ZnO and unintentionally doped n-type ZnO film wereprepared on GaAs substrate with the same method. A electroluminescence emissionassociated with defects was observed from the ZnO homojunction under forward currentinjection at room temperature. The EL spectra consisted of a wide band centered at～2.4.4 eV（FWHM,～0.47 eV） and a weak right shoulder centered at～2.9 eV. Furthermore, Theheterojunction light-emitting diode with n-Zn0.8Mg0.2O/ZnO/p-Zn0.8Mg0.2O structure wasgrown. A distinct visible electroluminescence with a dominant emission peak centered at450 nm and an emission peak centered at～520 nm were observed at room temperature fromthe heterojunction structure under forward bias conditions. The origin of electroluminescence emission was supposed to be attributed to a radiative recombination through deep-leveldefects in the ZnO active layer.（3） As diffusion p-type ZnO films were successfully prepare by pulsed laser deposition.Based on the achievement of p-type ZnO films, p-ZnO/n+-GaAs heterojunction light emittingdevice was successfully fabricated by pulsed laser deposition. The electroluminescenceemission was in the blue and ultra red region, which was coincidence with thephotoluminescence spectra of deep-level emission from ZnO layer and GaAs layerrespectively. In addition, the ZnO light emitting device with n-ZnO/p-ZnO/n+-GaAs structurewas grown by pulsed laser deposition. As-doped ZnO film by diffusion of As from thesubstrate was used for the p-type side and Al-doped ZnO film for the n-type side of the device.Distinct electroluminescence spectrum consists of a dominant emission peak at～2.5 eV and aweak shoulder centered at～3.0 eV was observed at room temperature. The I-V characteristicof the ZnO homojunction showed a good rectifying behavior with a turn-on voltage of～4.5 Vand a reverse breakdown voltage of～9 V.