DETERMINING PERIOD VARIATIONS IN A DISTRIBUTED-BRAGG-REFLECTOR THROUGH HIGH-RESOLUTION X-RAY-ANALYSIS

We studied the structural properties of a GaAs/AlAs distributed Bragg reflector using high resolution X-ray techniques. We evaluated diffrac tion and reflection scans by considering several possible structural d efects including period and individual thickness variations, compositi onally graded interface layers, and interfacial roughness. Diffraction scans provided information on layer thicknesses and crystalline quali ty. Both X-ray diffraction and reflectivity curves were compared to ca lculated curves using dynamical theory and Fresnel multilayer theory, respectively. X-ray reflectivity measurements and triple axis reciproc al space measurements showed the interfaces to be abrupt, and the supe rlattice to deviate from perfect periodicity. Together, these techniqu es provided a detailed analysis of superlattice parameters. The standa rd deviation of layer variations was shown to be 1.5-2.0% for the quar ter-wave stacks. We also present for the first time, the sensitivity o f X-ray reflectivity measurements to period deviation, and use recipro cal space maps to distinguish period dispersion from interface roughne ss. The results indicate the accuracy of high resolution X-ray techniq ues for quantitative superlattice analysis.