缺陷对β-Ga_(2)O_(3)薄膜的结构和光学特性的影响

Effect of defects on the structural and optical properties of β-Ga_(2)O_(3) thin films

采用射频磁控溅射技术和后期退火在蓝宝石衬底上成功制备了β-Ga_(2)O_(3)薄膜。借助于X射线衍射(XRD)、拉曼散射光谱(Raman)、X射线光电子能谱(XPS)、以及二次离子质谱(SIMS)研究了缺陷对β-Ga_(2)O_(3)薄膜的结构和光学特性的影响。结果表明,未退火的Ga_(2)O_(3)薄膜呈现非晶态,随高温退火时间逐渐增加,非晶Ga_(2)O_(3)薄膜逐步转变为沿(-201)方向择优生长的β-Ga_(2)O_(3)薄膜。所有Ga_(2)O_(3)薄膜在近紫外到可见光区的平均透过率都高达95%,β相Ga_(2)O_(3)薄膜的光学带隙比非晶态薄膜增加~0.3 eV,且随退火时间的增加,β-Ga_(2)O_(3)薄膜的光学带隙也随之变宽。此外,发现非晶Ga_(2)O_(3)薄膜富含氧空位缺陷,高温退火处理后,β-Ga_(2)O_(3)薄膜中的氧空位浓度明显降低,但蓝宝石衬底中的Al极易扩散至Ga_(2)O_(3)薄膜层,并随退火时间的增加Al浓度明显增加,氧空位的降低和Al杂质的增加是导致β-Ga_(2)O_(3)薄膜光学带隙变宽的主要原因。

β-Ga_(2)O_(3) thin films are successfully prepared on sapphire substrates by radio frequency magnetron sputtering technology and post-annealing.The effects of defects on the structural and optical properties ofβ-Ga_(2)O_(3) thin films are investigated by means of X-ray diffraction(XRD),Raman scattering spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),and secondary ion mass spectrometry(SIMS).The results show that the unannealed Ga_(2)O_(3) film exhibits an amorphous state.With the gradual increase of high-temperature annealing time,the amorphous Ga_(2)O_(3) film gradually transforms into aβ-Ga_(2)O_(3) film grown preferentially along the(-201)direction.The average transmittance of all Ga_(2)O_(3) films in the near ultraviolet to visible region is as high as 95%.The optical band gap of theβ-phase Ga_(2)O_(3) film increases by~0.3 eV compared with the amorphous film,and as the annealing time increases,the optical band gap ofβ-Ga_(2)O_(3) film also becomes wider.In addition,it is found that the amorphous Ga_(2)O_(3) film is rich in oxygen vacancy defects.After high temperature annealing,the oxygen vacancy concentration in theβ-Ga_(2)O_(3) film is significantly reduced,but Al impurities in the sapphire substrate is easily diffused into the Ga_(2)O_(3) film layer,and the Al concentration increases significantly with the increase of annealing time.The decrease of oxygen vacancies and the increase of Al impurities are the main reasons leading to the widening of the optical band gap ofβ-Ga_(2)O_(3) film.