Radiotracer spectroscopy of deep levels in the semiconductor band gap

Basic electronic properties of semiconductors are determined by defects and impurities. Extremely small relative concentrations may have an effect, if the impurity in question gives rise to a localized electron state having an energy within the band gap of the semiconductor. Among the techniques available to characterize band gap states, the present paper focuses on Deep Level Transient Spectroscopy (DLTS). To derive a definite chemical identification of the band gap states detected, radioactive isotopes are used as a tracer. Characteristic concentration changes of band gap states (detected by repeated DLTS measurements during the elemental transmutation) clearly reveal the involvement of a radioisotope in the formation of a certain defect level. The key issues of a radiotracer experiment are the radioactive doping process and the interpretation of transmutation-induced phenomena. Critical aspects are illustrated on the basis of recent radiotracer-DLTS studies in the semiconductors silicon and silicon carbide