Study Of Optical Properties And Structures Of MgZnO Alloys

Bandgap tuning engineering of MgZnO is a key step in the design of modern optoelectronic devices using zinc oxide?ZnO?materials,to create barrier layers and quantum wells in the device heterostructure.To achieve such optoelectronic devices,two important requirements should be met:p-type doped ZnO and bandgap tuning engineering.Bandgap of MgO and ZnO are 7.9eV and 3.4eV,respectively,thus Mg_xZn_1-xO alloy can broaden the bandgap of ZnO.In theory,the bandgap of the alloy can be continuously adjusted from 3.4 eV to 7.9 eV by changing the value of x.Mg_xZn_1-xO is suitable for the growth of ZnO superlattices,quantum wells and heterojunction structures.In this paper,Mg_xZn_1-xO alloys?x?0,0.01,0.06,0.1,0.14?with different Mg contents were grown on Al₂O₃ substrates by MOCVD system.Raman spectra at room temperature excited by 325 nm and PL spectra excited by 266 nm were measured.The ellipsometric spectra at room temperature were measured and analyzed and fitted with Eometrics software.XPS measurements were used to calculate the values of x in Mg_xZn_1-xO alloys.The X-ray absorption fine structure was measured and analyzed.The main work of this paper is:?1?PL spectrum at room temperature of Mg_xZn_1-xO alloys excited by 266nm laser was measured.Band gap of the Mg_xZn_1-xO alloys material is calculated:when x?0,0.01,0.06,0.1,and 0.14,the band gaps are 3.30eV,3.38eV,3.47e,3.59eV,and 3.61eV,respectively.The band bending parameter b=2.36 was calculated.At x?0.01,a broad PL peak caused by vacancies and defects begins to appear at 500 nm,which increases significantly with increasing x.?2?The absorption coefficient a of Mg_xZn_1-xO alloys was obtained by fitting the ellipsometry of Mg_xZn_1-xO alloys at room temperature with the Tauc Lorentz model.The bandgap was obtained for the pattern of the square of a vs energy.The band gap of ZnO is approximately 3.27 eV.When x?0.01,the bandgap of Mg₀.01Zn₀.99O alloy is about 3.38eV,and it tends to increase with the increase of x.?3?Raman scattering spectra at room temperature excited by 325 nm shows that as the x increases from 0 to 0.14,the 1LO of Mg_xZn_1-xO alloys moves from 574.2 cm^-1 to 613.6 cm^-1;The of I₁LO/I₂LO changed with Mg component?x?was calculated.We found the ratio of I₁LO and I₂LO gradually increases as the content of Mg increases,indicating that the long-range part of the interaction between electron and phonon gradually decreases.?4?Through X-ray photoelectron spectroscopy experiments,it was proved that the Zn is at a singulated state in Mg_xZn_1-xO alloys.The x-values for XPS measurement calculated from X-ray photoelectron spectroscopy of Mg_xZn_1-xO alloys:when x?0,0.01,0.06,0.1,and 0.14 during preparation,the calculated values were 0,0.029,0.092,0.156,0.160,respectively.?5?By fitting the Zn-L3 edge spectrum of Mg_xZn_1-xO with IFFEFIT-Athena and Artemis software,it was found that the ss² of R_zn-Mg/zn tends to increase with increasing x value.The RMg/zn-O data shows that the bond length of Zn-O decreases as the component x increases.The EXAFS measurement of Zn L3 edge proved that the Mg ion mainly replaced the Zn ion in the Mg_xZn_1-xO sample,instead of changing the crystal structure.?6?The XANES spectra of Mg-K edge,O-K edge and Zn-L3 edge of Mg_xZn_1-xO alloys show that bonding bonds of different states appeared in the sample Mg₀.14Zn₀.86O.It was demonstrated that Mg and Zn in Mg_xZn_1-xOalloys does not tend to cluster,and even though they are clustered together at higher concentrations,the XANES spectral characteristics exhibited are still more or less the same as those in the case of lower Mg concentrations.