Preparation Of P-Type ZnMgO Thin Films Using Ga-N Codoping Method By Reactive Magnetron Sputtering

Zinc oxide (ZnO) is a novel II-VI compound semiconductor with a wide direct bandgap and a hexagonal wurtzite structure. In particular, ZnO is a potential candidate for applications in short-wavelength optoelectronic devices, including light emitting diodes (LEDs) and laser diodes (LDs), due to its direct wide bandgap 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 MgO is alloyed with ZnO, the band gap energy of ZnMgO ternary alloy can be tuned by varying the Mg composition, which gives ZnO extended application in ultraviolet region.ZnMgO alloy is an intrinsic n type semiconductor and it is rather difficult to realize p type conduction, so, it is still a main challenge to be overcomed. In this paper, Ga-N codoped p-type ZnMgO thin films were fabricated by using dc reactive magnetron sputtering (DC-RMS). Our work is summarized as below:1. Zn_1-xMg_xO:(Ga,N) thin films with good quality were prepared by DC-RMS. The effect of the content of Ga and Mg on the crystallinity, morphology and bandgap were studied. Chemical states of elements Zn, Mg, O, Ga and N in Zn_1-xMg_xO:(Ga,N) thin films were also analyzed carefully. The optical bandgaps of the as-grown films were obtained by extrapolation of transmittance spectra, and thus proved that the content of Mg determines bandgaps of Zn_1-xMg_xO films.2. We have prepared Ga-N codoped p-type Zn_0.9Mg_0.1O thin films with stable properties. For instance,p-type Zn_0.9Mg_0.1O thin film with a high hole concentration of 1.28×10¹⁸ cm^-3, a resistivity of 39.6 Ωcm and a Hall mobility of 0.123 cm²V^-1s^-1 was prepared under 80% NH3 on glass substrate, and a hole concentration of 2.28×10¹⁷cm^-3, a low resistivity of 27.7 Ωcm and a Hall mobility of 0.989 cm²V^-1s^-1 was prepared under 100% N₂O on SiO₂/n-Si substrate. The effect of N₂O partial pressure and substrate temperature on p type conversion, carrier concentration, and resistivity were studied systematically. As experimental results shown, the as-grown films exhibit good crystallnity and compactsmooth surface morphology. Substrate temperature plays an even more important role in the electrical properties of the films, and p type conversion can only be realized in a certain range of temperature. According to our results, the optimal growth temperatue is about 540℃.3. We also tried to optimize other important growth parameters, such as substrate style, and thermal annealing temperature. For instance, the as-grown film exhibite a hole concentration of 2.87×10¹⁵ cm^-3, a low resistivity of 13400 Ωcm and a Hall mobility of 0.162 cm²V^-1s^-1, and the film shows a hole concentration of 3.09×10¹⁷ cm^-3, a low resistivity of 77.4 Ωcm and a Hall mobility of 0.261 cm²V^-1s^-1 after annealing at 450℃ and under pure O₂.4. We have fabricated a simple n-Si/p-ZnMgO heterojunction, and gave its I-V characteristic. At last, we tried to design and optimize some simple p-n junction structures.