Trap Level Measurements in Wide Band Gap Materials by Thermoluminescence

The electrical and optical properties of wide band gap materials are greatly affected by the presence of defects in the band gap. Identification and characterization of these defects that act as electron and hole traps are essential to understand charge carrier and exciton dynamics and ultimately control the electrical and optical properties of dielectrics and semiconductors. In this chapter, we will demonstrate how thermoluminescence (TL) spectroscopy can be used to characterize traps and measure their energy levels in the band gap. An advanced wavelength-based TL spectrometer will be presented, and its applications for the evaluation of trap levels and the characterization of donors and acceptors in semiconductors and dielectrics will be discussed

Optoelectronic Properties of Wide Band Gap Semiconductors

Wide band gap oxide semiconductors exhibit a wide range of interesting electronic and optical properties that have been used in optoelectronic devices. Native defects play a significant role in oxide semiconductors and affect their optical and electrical properties. In order to use these materials in devices, understanding and controlling defects are crucial. The focus of this thesis is to study defects in two important wide band gap oxides, strontium titanate (SrTiO3) and gallium oxide (Ga2O3). A wide range of characterization techniques were employed to study the optical and electrical properties of both oxides. The first part of this thesis focuses on enhancing the understanding of photoconductivity and luminescence phenomena in bulk SrTiO3 single crystals. The measurements show that there is a strong correlation between photoconductivity and defect concentration when sub band gap visible light is used as an illumination source. Positron annihilation spectroscopy suggested that Ti-vancacy is behind the photoconductivity phenomena in SrTiO3 single crystals. We also observed an interesting luminescence behavior in SrTiO3 single crystals, that has never been observed in other systems. We believe that the unusual behaviors in SrTiO3 luminescence are associated with the relaxation and expansion of the lattice during phase transition of SrTiO3. The second part of this work aims to investigate defects and electronic properties of epitaxial β-Ga2O3 thin films grown by metal organic chemical vapor deposition (MOCVD) technique on c-sapphire substrate. Thermoluminescence spectroscopy in conjunction with positron annihilation spectroscopy were used to identify the nature of defects and their activation energies. We found that annealing in various environments populate different types of defects. The measurements revealed the presence of large vacancy clusters which has been substantially increased by annealing in argon atmosphere. However, annealing in air modified the structure of defects by filling oxygen vacancies and increased the resistivity

Study of Trapping Phenomena in SrTiO\u3csub\u3e3\u3c/sub\u3e by Thermally Stimulated Techniques

Thermally stimulated current (TSC), thermally stimulated depolarization current (TSDC), and thermally stimulated luminescence (TSL) spectroscopies were combined to study trapping phenomena in undoped bulk SrTiO3 crystals. Electrical measurements were also performed and showed that the crystals are highly resistive in the dark but exhibited an unusually high photocurrent upon 400-nm illumination. Several traps were revealed in both TSC and TSDC spectra between 83 K and 450 K in such a broad temperature range and their activation energies were extrapolated from the trap positions (peaks). TSL spectra demonstrate similar characteristics comparable to TSC and TSDC spectra, though there are some differences because of different excitation and recombination mechanisms. This work reveals the presence of large number of traps in SrTiO3 single crystals, which are most likely the source of many of the interesting phenomena in SrTiO3 such as transient and persistent photoconductivity

Modeling of TiC-N thin film coating process on drills using particle swarm optimization algorithm

The prediction of maximum hardness in thin-film coating on high speed cutting drills is an essential prerequisite for developing drilling and it is depended on many factors such as ion bombard time, sub layer temperature, work and chamber pressure. This paper proposes the estimation of hardness of titanium nitride carbide (TIC-N) thin-film layers as protective of high speed cutting drills using Improved Particle Swarm Optimization-based Neural Network (PSONN). Based on the obtained experimental data during the process of chemical vapor deposition (CVD) and physical vapor deposition (PVD), the modeling of the coating variables for achieving the maximum hardness of titanium thin-film layers is performed. By comparison the experimental results with model estimation the accuracy of the system was approximately 97.47% acquired while back propagation (BP) had 95.5% precision.7 page(s

Study of Trapping Phenomena in SrTiO\u3csub\u3e3\u3c/sub\u3e by Thermally Stimulated Techniques

Thermally stimulated current (TSC), thermally stimulated depolarization current (TSDC), and thermally stimulated luminescence (TSL) spectroscopies were combined to study trapping phenomena in undoped bulk SrTiO3 crystals. Electrical measurements were also performed and showed that the crystals are highly resistive in the dark but exhibited an unusually high photocurrent upon 400-nm illumination. Several traps were revealed in both TSC and TSDC spectra between 83 K and 450 K in such a broad temperature range and their activation energies were extrapolated from the trap positions (peaks). TSL spectra demonstrate similar characteristics comparable to TSC and TSDC spectra, though there are some differences because of different excitation and recombination mechanisms. This work reveals the presence of large number of traps in SrTiO3 single crystals, which are most likely the source of many of the interesting phenomena in SrTiO3 such as transient and persistent photoconductivity