Advancing the Characterization of Semiconductors with Synchrotron Radiation

Abstract

The characterization of materials is a crucial step that enables their use in practical devices. With the goal of developing improved devices, the utility of advancing the manner in which materials are characterized is clear. In this work, novel characterization and analysis techniques that utilize synchrotron-based spectroscopic techniques are developed and employed to gain deeper insight into the electronic properties of material systems than would otherwise be possible. A variety of material systems are studied, which range from new phases of bulk semiconductors to materials that have been perturbed in some way, such as by the presence of dopants, intercalants, or vacancies. These materials are characterized using a variety of synchrotron-based spectroscopic techniques which range from core-level spectroscopy techniques that probe the occupied and unoccupied electronic density states of a material, to those which reveal the presence of localized defects. The electronic properties of the semiconductor ZnSiN2 have been studied using core-level spectroscopic techniques, yielding an electronic band gap of 4.7 ± 0.3 eV, in agreement with a calculated value of 4.5 eV. A new carrier-dependent excitation approach has been developed to detect and identify the origin of defects in semiconductor systems and gain qualitative insight into the carrier dynamics following X-ray excitation. Applied to ZnSiN2, this yields a hierarchy of mid-gap nitrogen vacancy defect levels. A new analytical approach has been developed to interpret a characteristic spectral feature of intercalated graphitic systems, called the pre-π* feature. The redistribution of spectral weight in this region is direct evidence of charge transfer between the intercalated ion and the host lattice. This is demonstrated in a study of PF6-intercalated graphite, in which charge is transferred from the host lattice to the intercalant anion. The electronic properties of several other semiconductor systems have also been studied. The band gap of MgSiN2 has been determined to be 5.6 ± 0.2 eV, in agreement with a calculated value of 5.7 eV. The band gap of the Ia-3, R-3c and Pbcn polymorphs of In2O3 have been determined to be 3.2 ± 0.3, 3.1 ± 0.3 and 2.9 ± 0.3 eV, respectively. This is in agreement with respective calculated values of 3.3, 3.3 and 2.9 eV determined for the Ia-3, R-3c and Pbcn In2O3 polymorphs, respectively.