物理学报2016，Vol.65Issue(13)：130702-1-130702-7,7.DOI:10.7498/aps.65.130702
纤锌矿GaN外延层薄膜热膨胀行为的变温Raman散射研究∗
Thermal expansion b ehaviors of epitaxial film for wurtzite GaN studied by using temp erature-dep endent Raman scattering
摘要
Abstract
III-nitride materials have attracted considerable attention in the last decade due to their wide applications in solid-state light devices with their direct wide band-gaps and higher quantum efficiencies. InGaN/GaN multiple quantum well is important active region for light-emitting diode, which can be tuned according to indium composition in the InxGa1−xN alloy system. Owing to difficulty in fabricating bulk materials, GaN thin films are heteroepitaxially grown on lattice-mismatched and thermal-expansion-mismatched substrates, such as sapphire (Al2O3), Si and SiC, which sub-sequently results in a mass of threading dislocations and higher residual strains. On the one hand, dislocations and defects existing in GaN epifilms trap the carriers as scattering centers in the radiative recombination process between electrons and holes, and play an important role in drooping the internal quantum efficiency. On the other hand, higher built-in electric field induced by residual strains existing in GaN epifilm could make the emission wavelength red-shifted. It is common knowledge that temperature is one of the important factors in the growth process of epitaxial films, as a result, further research on thermal expansion behaviors is needed. Based on the above analysis, an in-depth study of thermal expansion behavior of wurtzite GaN epitaxial film is of vital importance both in theory and in application. In this study, we investigate the thermal expansion behaviors of wurtzite GaN epitaxial films by using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K. According to the physical implication, Gruneisen parameter is almost a constant (Gruneisen parameters of all phonon modes are in a range between 1 to 2 for GaN) that characterizes the relationship between the phonon shift and the volume of a solid-state material. More importantly, Gruneisen parameter is relatively insensitive to temperature and suitable for building the connection between the phonon shift and thermal expansion coefficient. Therefore, the linear relationship between the phonon shift and temperature is built and utilized to calculate the thermal expansion coefficient according to the physical implication of the Gruneisen parameter. Conclusions can be obtained as follows. 1) The thermal expansion coefficient of GaN epifilm can be cal-culated in a certain temperature range by measuring the phonon modes of E2 (high), A1 (TO) and E1 (TO) through using temperature-dependent Raman scattering when the corresponding Gruneisen parameters are determined. 2) The calculated thermal expansion coefficients of GaN epifilm are consistent with the theoretical values. Conclusions and methods in this paper provide an effective quantitative analysis method to characterize the thermal expansion behaviors of other III-nitride epitaxial thin films, such as AlN, InN, AlGaN, InGaN, InAlN etc., which can be of benefit to reducing the dislocation density and improving the luminescence efficiency of light emitting diode. There-fore, research on thermal expansion behaviors of epifilms using temperature-dependent Raman scattering has a directionfor further studying the latter-mismatch and thermal-expansion-mismatch between the epitaxial film and substrate.关键词
外延层薄膜/热膨胀系数/Gruneisen参数/变温Raman散射Key words
epitaxial-film/thermal expansion coefficient/Gruneisen parameter/temperature-dependent Raman scattering引用本文复制引用
王党会,许天旱,宋海洋..纤锌矿GaN外延层薄膜热膨胀行为的变温Raman散射研究∗[J].物理学报,2016,65(13):130702-1-130702-7,7.基金项目
陕西省自然科学基础研究项目(批准号:2015JM6327)、陕西省教育厅科学研究计划(批准号:2016JK1593)、西安石油大学博士科研启动基金(批准号：Z14086)、西安石油大学材料加工工程重点学科(批准号：YS32030203)和陕西省大学生科研创新训练项目资助的课题.* Project supported by the National Science Foundation of Shaanxi Province, China (Grant No.2015JM6327), the Scientific Research Program of Shaanxi Provincial Education Department, China (Grant No.2016JK1593), the Youth Science and Technology Innovation Fund of Xi’an Shiyou University, China (Grant No. Z14086), the Key Subject of Materials Processing Engineering of Shaanxi Province, China (Grant No. YS32030203), and the Scientific Innovation and Training Project of College Students in Shaanxi Province, China （批准号:2015JM6327）
