Hazu Kouji, Chichibu Shigefusa F
Center for Advanced Nitride Technology, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan.
Opt Express. 2011 Jul 4;19 Suppl 4:A1008-21. doi: 10.1364/OE.19.0A1008.
Light polarization characteristics of the near-band-edge optical transitions in m-plane AlxGa1-xN epilayers suffering from anisotropic stresses are quantitatively explained. The epilayers were grown on an m-plane freestanding GaN substrate by both ammonia-source molecular beam epitaxy and metalorganic vapor phase epitaxy methods. The light polarization direction altered from E [symbol see text]c to E//c at the AlN mole fraction, x, between 0.25 and 0.32, where E is the electric field component of the light and [symbol see text] and // represent perpendicular and parallel, respectively. To give a quantitative explanation for the result, energies and oscillator strengths of the exciton transitions involving three separate valence bands are calculated as functions of strains using the Bir-Pikus Hamiltonian. The calculation predicts that the lowest energy transition (E1) is polarized to the m-axis normal to the surface (X3) for 0< x ≤ 1, meaning that E1 emission is principally undetectable from the surface normal for any in-plane tensile strained AlxGa1-xN. The polarization direction of observable surface emission is predicted to alter from c-axis normal (X1) to c-axis parallel (X2) for the middle energy transition (E2) and X2 to X1 for the highest energy transition (E3) between x = 0.25 and 0.32. The experimental results are consistently reproduced by the calculation.
对承受各向异性应力的m面AlxGa1-xN外延层中近带边光学跃迁的光偏振特性进行了定量解释。这些外延层通过氨源分子束外延和金属有机气相外延方法生长在m面自支撑GaN衬底上。在AlN摩尔分数x介于0.25和0.32之间时，光偏振方向从E⊥c变为E//c，其中E是光的电场分量，⊥和//分别表示垂直和平行。为了对该结果进行定量解释，使用Bir-Pikus哈密顿量计算了涉及三个独立价带的激子跃迁的能量和振子强度作为应变的函数。计算预测，对于0 < x ≤ 1，最低能量跃迁（E1）偏振到垂直于表面的m轴（X3），这意味着对于任何面内拉伸应变的AlxGa1-xN，从表面法线方向基本上无法检测到E1发射。对于中间能量跃迁（E2），可观测表面发射的偏振方向预计从c轴法线（X1）变为c轴平行（X2），对于最高能量跃迁（E3），在x = 0.25和0.32之间，偏振方向从X2变为X1。计算结果与实验结果一致。
