X-Ray Diffraction Characterization of the Thermal Annealing Effects on InxGa1-xN-GaN MQWs

• Main Authors: Chu-Ching Tsai, 蔡竹青
• Other Authors: Hsueh-Hsing Hung
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/38270239579124966376

碩士 === 國立清華大學 === 工程與系統科學系 === 90 === We apply X-ray diffraction to characterize the structure of InxGa1-xN-GaN MQWs and study the effect of thermal-annealing from the structural point of view. Surface-normal (00.2) and (00.4) diffraction profiles were collected and analyzed by numerically fitting with the dynamical theory of X-ray diffraction. In our sample system, the measured value of molar fraction x of indium composition in InxGa1-xN layers is 0.17 (±0.01), which has been verified by solving a modified relation of elasticity, given by us for the first time, valid to the strained InxGa1-xN-GaN bilayer. According to mesh scans around the zeroth-order of (00.2) super-lattice reflection of sample at different post-annealing temperatures, we observed an asymmetric tendency of the diffraction contours evolving to two peaks. This observation implies that two distinct values of indium composition are well separated in the 1000°C-annealed MQWs sample. The proposed interpretation was supported by X-ray reflectivity data and consistent with the splitting of emission peak shown in the PL spectrum. From the photoelectronic point of view, according to the blue shift and varying of FWHM observed in PL and XEOL spectra, we indicate that the interface roughness is an important factor in the formation of an extra and larger bandgap in addition to the ordinary bandgap of quantum wells. Thermal activation initiated the interdiffusion of In and Ga ions at rough interfaces. High-temperature annealing would promote the inter-diffuse process and then diffusion layers at interface were gradually formed. Sharper interfaces were achievable if sample annealed further at high temperatures; even though, fully coherent strains were still remained in the 1000°C-annealed sample. The compositional variation at interface turned out to be a certain subband layer of quantum wells, because the as-grown roughness transformed into smooth diffusion layers by annealing.