Opto-electronic study of phosphorus-doped n-type and hydrogen-doped p-type CVD diamond films.

摘要

In this thesis the first active {lcub}111{rcub} n-type phosphorous doped n-type CVD diamond films are studied by means of different photocurrent-based techniques. Two new defect levels, X_P1 and X_P2, were detected. X_P1 was identified as the substitutional phosphorous donor, situated 0.6 eV under the conduction band. X_P2, a defect with a photoionisation onset of ∼0.81 eV, is only present in highly resistive films and remains unidentified. This defect, which deteriorates the conductive properties, can be P- as well as H-related.; Quasi-steady-state photocurrent measurements at low temperatures show oscillatory photoconductivity. Using a LO-phonon of 155 meV, four excited states of phosphorous could be determined. They are respectively situated at 523 meV, 563 meV, 575 meV and 584 meV above the P-ground state. These data were confirmed by using photothermal ionisation spectroscopy.; Dielectric measurements in the 45 Mhz–20 GHz range were performed on different quality CVD diamond samples. Oxidised and hydrogenated samples were measured in air at room temperature. While the polished film only showed strong DC conductivity, the unpolished hydrogenated films showed a clear near-Debye dielectric response around 108–109Hz. This was attributed to 2D plasmons, formed by the hole accumulation layer (1013 holes cm−2) present on such films. The response was clearly film quality dependent, which can be explained by the different hydrogen coverage on the surface of the diamond films. After a 1h anneal at 200°C in a vacuum pumped quartz tube, the dielectric response disappeared, giving the same results as the oxidised samples, proving the origin of the dielectric relaxation to be hydrogen. This corresponds to the reported disappearance of the surface conductivity at 200°C. A reappearance of the dielectric relaxation after exposing the sample to air is not seen.