Semiconductor and their structure characterization using terahertz excitation spectroscopy

In this work, the properties of semiconductors and their structures were determined using the THz-TDS emission spectroscopy method. First of all Indium Phosphide (InP) was investigated. THz pulse emission spectra of (111) n and (100) SI-type THz were measured. From which the position of the L-valley was determined to be 0.75 eV. There were also some differences near forbidden energy gap. This was explained by the competing effects of surface electric field and photo-Dember. The first dominates up to 1.63 eV, and the second one above this value. The measured azimuthal dependencies (111) and (100) have proven that there is a nonlinear current effect due to anisotropic photoconductivity. The dependence of sin (2φ) on the plane (100) showed that the dominant effect is OR (optical rectification). After that, the position of the conduction band offset was determined in In0.53Ga0.47As/InAlAs heterojunction. When measuring the layers of different thicknesses, it was observed that by lowering thickness of emitting layer will result to more expressed conduction band offset in the spectra. From these measurements, the conductivity and valence bands were determined to be 0.43 eV and 0.28 eV respectively. Their distribution ratio 60/40 corresponds to previously determined value. This shows the reliability of this method. After checking this methodology, a Ga1-xBixAs/GaAs heterojunction was measured using different bismuth concentration. From these measurements, we found that the variation in the bismuth amount changes the offset of both the conductivity and the valence band. The data obtained complied to theoretical calculations with a small amount of bismuth. And the conductivity bandwidth ratio is 45/55. However, specimens with high bismuth levels cause rapid shift of valence band offset. However, further studies are needed to confirm this