Deposition Of P Type ZnMgO Thin Films By DC Reactive Magnetron Sputtering

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, including light emitting diodes (LED) and laser diodes (LD), due to its direct wide-bandgap (3.37 eV at room temperature)and high exciton binding energy (60 meV, cf. 25 meV for GaN), which will favor efficient excitonic emission processes at room temperature. What is more, when Magnesium is added 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 Thesis, Al-N codoping method which was used for the p type doping of ZnO thin films has now been used for the doping of ZnMgO thin films, and through this doping method, stable p type ZnMgO thin films have been deposited. From the performance analysis of these thin films, optimal growth parameters have been derived, under which ZnMgO thin films with best performance can be deposited which finally lay the foundation for the preparation of ZnO-based optoelectronic devices.The main content of the thesis is as follows:P type ZnMgO thin films have been prepared by Al-N method using DC reactive magnetron sputtering.The effect of the substrate temperature, the ratio of N₂O flow and substrate types on the crystallization properties, surface morphology, and especially, the electrical properties of the thin films have been studied. The results showed that p-type conductivity have been realized in the substrate temperature range of 400-530℃, and at the temperature of 530℃, thin Film with the best electrical properties have beenobtained, which have a resistivity of 58.5 Ωcm, Hole concentration of 1.95×10¹⁷cm^-3. As to the ZnMgO thin films deposited at the same substrate temperature, when the flow ratia of N₂O have the relationship of N₂O/(O₂+N₂O)≥0.4, the thin films show p-type conductivity,specially When N₂O/(O₂+N₂O)=0.7, the films show the best crystallization properties and c-axis preferred orientation, and resistivity at this time is the minimum. The thin films prepared on three different substrates have increasing crystallization properties at the order of glass, quartz, Wafer,Electrical performance test shows silicon substrate itself will affect the test results.Comparing with N-doped ZnMgO films, the electrical properties of co-doped thin films are improved, the hole concentration increases three order magnitude and the resistance decreases two order magnitude. The XPS analysis of p type and n type ZnMgO thin films testifys the existing of Al-2N complex, and it also shows that there are two chemical environment of N in the ZnMgO thin films, which are N_o and (N₂)_o,and a conclusion is reached that the conduction type of thin films depend on the relative concentration of No and (N₂)o, When N_o dominant, films show p-type conductivity, otherwise,when (N₂)_o dominant, films show n-type conductivity,so N_o is the ideal location of p-type doping.The band gap of ZnMgO thin film is tunable by varying the content of Magnesium in the films.