金属有机物化学气相沉积法制备的锰掺杂氮化镓薄膜的结构和光学性质

Structural and optical properties of Mn-doped GaN by metal organic chemical vapor deposition

为研究锰价态对掺杂氮化镓薄膜的光学性质影响,采用金属有机物化学气相沉积技术在不同的温度下生长锰掺杂的氮化镓外延薄膜材料。采用原子力显微镜探测不同温度下生长的样品表面;X射线光谱仪探测样品中锰的化学价态;光致荧光谱仪测量不同样品的可见光段和红外波段的光学性质。测试结果表明在900~980℃温度范围,样品表面平整无杂相;此范围为优化的生长温度。其后,在优化的生长温度下,生长重掺杂薄膜样品;X光谱仪测试结果表明锰以2价或3价态形式代替镓原子存在。光致荧光谱测试结果表明,除了在可见光的紫光波段,所有样品均具有8个精细发光结构,不受生长温度影响之外,在其他测试范围,发光性质取决于生长温度。对于在低温下生长的薄膜,可探测到较强的天蓝色发光带,这个发光带是与镓金属在表面积累相关;而对于在相对较高温度下生长的薄膜,可探测到较强的红外发光带,并且具有零声子线和声子伴线的精细结构特征。这个红外发光带是Mn^(3+)内电子自旋允态的~5 T_2→~5 E跃迁而引起的展宽的零声子线和声子伴线;并且声子伴线分别对应于GaN特征拉曼散射峰。上述结果表明,生长温度发生改变,氨气分解产生变化,导致氮空位发生变化,可以使得锰掺杂氮化镓中锰离子充电或放电,改变了价态,从而改变了材料的光学性质。此规律为人工制备具有不同光学性质的材料提供参考。

To study the effects of Mn valences on optical properties,Mn-doped GaN epitaxial films were grown on sapphire substrates（0001）by metal organic chemical vapor deposition（MOCVD）at various temperatures.Surfaces of films grown at various temperatures were characterized by atomic force microscopy;valences of Mn ions in films were investigated by X-ray photoelectron spectroscopy;Photoluminescence measurements were performed within visible light and ultraviolet wavelength band.It was revealed that high quality films with smooth surfaces were grown at temperatures from 900 to 980℃,which were optimized temperature window for film growth.After that,heavy Mn-doped GaN were grown at optimized temperature windows.It was found that Mn ions existed at Ga substituting sites as Mn^3＋ and/or Mn^2＋in films.Photoluminescence measurements revealed that optical properties of films were altered with the growth temperature except that in violet wavelength band,during which fine structures with 8peaks were detected for each film.In detail,for 900℃-grown film,broad aquamarine luminescence band around 484 nm was pronounced in spectra,which was attributed to excess Ga in GaN;for films grown at relatively higher temperature of 930℃ and 980℃,Infrared emission band could be detected with Mn-related zero phonon line（ZPL）at 1.414 eV and its phonon replicas.The infrared emission band was assigned to the internal ^5 T2→^5 E transition of the neutral Mn^3＋ state with broadening ZPL and its replicas,which were featured of GaN Raman spectra.These data indicated that nitrogen vacancies were altered due to different decomposition of NH3 in varied growth temperatures.This leads to the charge or discharge of Mn ions,and then the change of Mn valences and optical properties of Mn-doped GaN films.The effects of growth temperatures supported to change artificial optical properties of Mn-doped GaN.