Basic electronic and optoelectronic properties of threading dislocations in heteroepitaxial diamond

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The proposal aims at a comprehensive study of the intrinsic electronic & optoelectronic properties of dislocations in diamond. According to general experience with semiconductor materials, high dislocation densities can deteriorate the performance of devices drastically. As a consequence, they are studied intensively and strong efforts are made to minimize their density. Though vigorous activities have been launched to develop diamond-based electronic devices and dislocations have already been identified as major structural defect, our knowledge on their basic properties is rather poor. This is mainly due to the absence of well-defined samples. The group of the applicant has developed a heteroepitaxy technique that recently facilitated the synthesis of a single crystal diamond disc with a diameter of ~90 mm. Their approach has the potential to remove a major hurdle in device development, i.e. the unavailability of wafer-size substrates. In addition, this method enables now the controlled preparation of crystals containing dislocations with defined propagation direction and densities varying over 4 orders of magnitude as required for systematic studies. The planned work will start with a full spectroscopic characterization of samples with defined dislocation densities and line vectors by UV/Vis- and IR-absorption, photoluminescence (PL) and cathodoluminescence (CL). Next, a setup for spectrally resolved photoconductivity (SPC) and thermally stimulated currents (TSC) will be constructed. The subsequent measurements will identify and quantify electrically active defect levels. In the framework of several collaborations, charge collection efficiency (CCE) and charge transient spectroscopy (QTS) measurements will be performed in order to derive density, capture cross section and depth of traps, separately for electrons and holes. Next, the diffusion coefficient and the lifetime of charge carriers will be determined by two pump-probe techniques. Finally, the material will be used to produce devices (detectors, electronic devices). Besides insight in the intrinsic electronic properties of dislocations, critical thresholds for their density in different applications will be derived, that can provide benchmarks for devices development.