Deep-level transient spectroscopy for defect characterization in dielectric materials

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The physical properties of solid-state materials are determined, to a large extent, by defects. This is especially true for the electrical properties of semiconductors and insulators, where a variety of methods have been established to characterize defects with respect to their optical and electrical properties. The most common electrical characterization method for semiconductors is the so-called deep level transient spectroscopy (DLTS), where controlled electrical charging and discharging within a depletion region gives access to two characteristic parameters (as a fingerprint of the defect): the capture cross section and the activation energy. As conventional DLTS is limited to defects in such a space charge (depletion) region of a Schottky or p-n junction, a method for electrical defect characterization in dielectric (insulating) materials is missing. Within this project, a new method to study deep defects in dielectric materials will be further developed and optimized to characterize defects in insulators such as Al2O3, SiO2, TiO2 and GaN. It is a special optoelectrical technique that uses the boxcar evaluation method from DLTS in combination with a conductive layer (a two-dimensional electron/hole gas) that replaces the charge depletion region. The newly developed technique, called optical 2D-DLTS here, will expand the tool set for investigating defect levels in (undoped) dielectric materials. The starting point of this project will be an extension of the temperature range and bandwidth of the method, followed by an optimization of the read-out detector, i.e. the two-dimensional hole gas at the surface of an epitaxial-grown diamond layer. The long-term goal is to establish the optical 2D-DLTS method as a versatile tool to study defects in a broad range of dielectrics, grown on different detector materials (diamond, GaAs, Si, etc.).