利用X光繞射及光激發螢光光譜探討應力對單層氮化銦鎵/氮化鎵量子井之影響

Abstract

在本論文中，藉由X光繞射(X-ray Diffraction, XRD)及光激發螢光光譜(Photoluminescence, PL)討論單層氮化銦鎵/氮化鎵量子井之應力變化。樣品利用有機金屬氣相沈積磊晶方法，製備氮化銦鎵厚度由 4.9 nm 變化至300 nm，且在個別的樣品銦組成皆約為13 %。 光激發螢光光譜分別在室溫及 20K 進行量測。隨著氮化銦鎵厚度增加，和氮化銦鎵相關的發光頻譜位置往短波長處偏移，且由X光繞射結果觀察到氮化銦鎵的繞射峰往低角度處偏移，此變化趨勢與光激發螢光光譜一致。利用銦LIII 能量進行近邊緣X光吸收光譜來決定樣品內的銦組成及檢驗厚度效應對X光吸收性質之影響。但由於氮化銦鎵厚度太薄且激發光源能量太弱及範圍過短，因此厚度效應並未得知。 利用已知的氮化銦鎵相關的發光頻譜位置討論當氮化銦鎵厚度增加時由應力誘導產生的壓電場。推算出隨著量子井厚度從 4.9 nm增加到 300 nm, 應力產生的壓電場由 1.1 MV/cm 減小到 8.9 x10-3 MV/cm。並透過已知壓電場大小，適當的計算並討論樣品之物理性質。我們相信氮化銦鎵量子井之應力分佈會影響氮化銦鎵/氮化鎵光電元件的光學性質。

Photoluminescence (PL) and X-ray Diffraction (XRD) Spectra of strained single layer InGaN films sandwiched by GaN were performed to study the stain variation in layers of different thickness. The film thickness of InxGa1-xN grown with MOCVD varied from 4.9 nm to 300 nm and the In concentration was about 13 molar percentages (x = 0.13). Photoluminescence measured at ambient temperature and 20 K both indicated a non-linear blue shift of the indium related PL peak position in increasing layer thickness. The XRD results exhibited shifts of diffraction peaks towards lower Bragg angles in the direction of layer thickness increasing, consistent with the PL results. Near-edge x-ray absorption spectroscopy (XANES) was performed with In-LIII energies to determine the In concentration and to examine the thickness effect of the films on x-ray absorption properties. The thinness of the In incorporated layer and the weakness and short energy range of the excitation source, however, derailed this attempt. The strain induced piezoelectric field was seen to relax with increasing InGaN layer thickness in a scale that rendered unto us the opportunity to quantify the effect. The induced electric field strength at room temperature was estimated from known the experimental data, which varied from 1.1 MV/cm for the 4.9 nm sample to 8.9 x 10-3 MV/cm for the 300 nm film, respectively. Upon the application of the found piezoelectric field, some mechanical properties pertinent to this quantity were also calculated and discussed. We believe the strain relaxation problem in InGaN quantum wells has to be accounted for in any serious InGaN / GaN light-emitting components as it affects the optical properties of these devices.