Preparation And Characterization Of Group-IA Element (Li, Na) Doped P-Zn_1-xMg_xO Thin Films

ZnO is anâ…¡-â…¥compound semiconductor with a wide direct bandgap of 3.3 eV and a large exciton binding energy of 60 meV at room temperature.In order to realize ZnO-based short-wavelength optoelectronic devices,e.g.light emitting dioes(LEDs) and laser diodes(LDs),one of the critical issues is to realize stable p-type doping and the other is the bandgap engineering of ZnO.Through varying the composition of MgO alloyed into ZnO,the band gap energy of hexagonal wurtzite Zn_1-xMg_xO ternary alloy can be tuned continuously.Other than the advantages mentions above,p-type Zn_1-xMg_xO is also the essential material constituting the LEDs working in the ultraviolet regionIn this research,Li or Na doped p-type Zn_1-xMg_xO thin films were fabricated by using dc reactive magnetron sputtering(DC-RMS)and pulsed laser deposition(PLD) technologies,respectively.The main content of this thesis is illustrated as follows:1)Zn_1-xMg_xO:Li(x=0.04,0.16)thin films with good crystallinity were prepared by DC-RMS.The effect of substrate temperature,anneal temperature,Li doped content and Mg alloyed content on the crystallinity,morphology,electrical and optical properties of the films are presented and discussed in this article.By annealing in the oxygen ambient,the crystallinity and p-type electrical properties of as-deposited thin films are improved obviously.The optimal electrical properties of the p-type Zn_0.96Mg_0.04O:Li,presenting a resistivity of 72.3Ωcm,a carrier concentration of 1.49×10¹⁷cm^-3,and a Hall mobility of 0.58 cm²V^-1s^-1,are achieved at the annealing temperature of 500℃.Furthermore,absorption edges of the room-temperature absorption spectra shift to higher energy as Mg content increases.The blue shift of optical band gap with increasing Mg content implies that Mg is an effect alloy element for band gap engineering in p-type ZnO films.2)Za_1-xMg_xO:Na(x=0.1,0.2)thin films with good quality were prepared by PLD. The influence of substrate temperature,O₂ pressure and Mg alloying composition on the crystallinity,morphology,electrical and optical properties are revealed in this article.The optimal electrical properties of the p-type Zn_0.8Mg_0.2O:Na was achieved at the substrate temperature of 650℃and the oxygen pressure of 48 Pa. The optimized film possesses a resistivity of 60.34Ωcm,a carrier concentration of 1.56×10¹⁷cm^-3,and a Hall mobility of 0.67 cm²V^-1s^-1.Through investigations on the optical properties of ZnO:Na,Zn_0.9Mg_0.1O:Na and Zn_0.8Mg_0.2O:Na,we find that the optical band gap of the films blue shift and the acceptor level deeper as Mg content increases.Furthermore,we have fabricated a p-Zn_0.8Mg_0.2O/n-ZnO heterojunction,consisting of a n-ZnO:Al layer on a p-Zn_0.8Mg_0.2O layer on Si substrate.This hetero-diode displays obvious rectification behavior in repeated measurements,therefor confirming the p-type conduction of the Zn_1-xMg_xO:Na thin films obtained.