Some Advanced Microwave Techniques for the Investigation of Defect States in Semiconductors

Publisher Website
Google Scholar
Abstract
The application of microwave techniques to the investigation of electronic defect properties relies on either of two principles: (i) resonant effects due to spin transitions (EPR) or (ii) non-resonant absorption due to free carriers, which originate from defects. Examples for both types are reviewed: The combination of ESR (i) with optical excitation allows in favourable cases characterization of deep defect levels with respect to their chemical nature and their local symmetry, and thresholds for photo-ionization and deionization can be obtained. Free carrier absorption (ii) can be utilized in order to monitor the emission of carriers from deep impurity states in a space charge region. This transient Microwave-Absorption Spectroscopy is shown to provide considerably higher bandwidth than conventional capacitance spectroscopy at comparable sensitivity. Finally, magneto-oscillations of the Shubnikov-de Haas type (iii) can be used for a precise determination of the free carrier concentration. In the zero gap compound HgSe: Fe, the simultaneous observation of the Fe3+-ESR and the magneto-oscillations allows investigation of the self-ionizing resonant donor level, Fe2+/3+.