| Summary: | 碩士 === 國立交通大學 === 電子物理系 === 90 === 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.
|
|---|
