Preparation And Characteristics Of In-N Co-doped P-type ZnO And ZnMgO Thin Films

Zinc oxide(ZnO)is a II-VI compound semiconductor with a wide direct bandgap and a hexagonal wurtzite structure. ZnO is a unique material that exhibits optoelectronic, piezoelectric and ferromagnetic multiple properties, Particularly, it is a potential candidate for applications in short-wavelength optoelectronic devices, due to its direct wide-bandgap(3.37eV at room temperature)and high exciton binding energy(60meV, cf. 25meV for GaN), which will favor efficient excitonic emission processes at room temperature. What is more, when Magnesium is doped into ZnO, the band gap of ZnMgO thin films can be tuned by varying the content of Magnesium, which gives ZnO extending application in ultro-violet region.Intrinsic ZnO exhibits n-type conductivity, there are some reports that good n type ZnO thin films have been deposited by doping with elements like Aluminium or Gallium, but it is difficult to fabricate p-type ZnO films because of self-compenstion and low solubility of acceptor. The p type doping of ZnMgO thin films is also in the same case. In this work, we mainly concern about this issue, and moreover this work is also expended from it. P-type ZnO and ZnMgO thin films codoped with In-N were prepared using DC reactive magnetron sputtering. Our work is as below:1. P-type ZnO thin films had been prepared by In-N codoped method using N₂O as the N doping source. The effect of the substrate temperature and the ratio of N₂O flow on the properties of films had been studied. The results showed that p-type film with the best electrical properties had been obtained at the temperature of 550℃, which had a resistivity of 35.6Ωcm, Mobility of 0.111cm² V^-1·s^-1 and Hole concentration of 1.57×10¹⁸cm^-3. P-type can only realized in a certain ratio region and when N₂O/ (O₂+N₂O) = 0.7, the films got the best p-type properties.2. P-type ZnO thin films had been prepared by In-N codoped method using NH3 as the N doping source. The effect of the substrate temperature,the ratio of O₂ flow and the In content in the target on the properties of films had been studied. The results showed that p-type film with the best electrical properties had been obtained at the temperature of 580℃Ω, with a Resistivity of 53.9Ωcm, Mobility of 0.456cm² V^-1·s^-1 and Hole concentration of 2.54×10¹⁷cm^-3. The films got the best p-type properties with a Resistivity of 40.1Ωcm, Mobility of 0.344cm²V^-1·s^-1 and Hole concentration of 4.52×10¹⁷cm^-3 when the ratio of O₂ is 50%. The optimized In content in the target is about 0.5at. %, at which the film showed best p-type conduction.3. The effect of Mg content on the crystallization properties, surface morphology, and especially, the band gap of ZnMgO films had been studied. It was proved that the content of Mg determined the band gap of the ZnMgO films.4. The effect of Mg content on the crystallization properties, surface morphology, and especially, the band gap of In-N codoped p-type ZnMgO thin films had been studied and the optimized conditions were concluded.5. Silicon-based heter-structure pn junctions comprising an p-Zn^0.95Mg^0.05O:(In,N) layer on a n-Si layer displayed apparent electrical rectification in repeated measurements thereby confirming the formation of a typical pn junction, which also confirmed the p-type conduction of the In-N codoped Zn^0.95Mg^0.05O thin films.