Uticaj fotogenerisanih nosilaca naelektrisanja na termalne i elastične osobine silicijuma n-tipa

Abstract

This thesis presents a complete theoretical and experimental analysis of the influence of photogenerated carriers on the dynamic component of temperature distribution and the thermoelastic component of n-type silicon photoacoustic signal illuminated by a modulated monochromatic light source for modulation frequencies ranging from: 1 Hz to 107 Hz (theory) and 20 Hz to 20 kHz (experiment). Analyzes were performed for different sample thicknesses, different surface qualities and different carrier lifetimes. Most of the analysis is based on comparing the amplitude and phase of temperature and photoacoustic signals with and without the presence of photogenerated carriers. Special attention was paid to finding characteristic patterns of behaviour that were observed through the presence of clearly expressed peaks of the amplitude ratio and phase differences between the temperatures on the front and back surface of the sample. The existence of these peaks can be interpreted as unambiguous indicators of the presence of photogenerated carriers in a semiconductor sample. It was noticed that similar structures in the form of peaks occur at the amplitudes of the thermoelastic component of the photoacoustic signal so that the peaks are more intense in samples whose thickness is less than the value of the diffusion length of the carriers, ie. in plasma-thin samples. Higher peak intensity implies a decrease in the value of the amplitude of the thermoelastic component of the photoacoustic signal at lower modulation frequencies, which makes this component "invisible" for observation in a real experiment. The results presented in this thesis indicate that this decrease in the amplitude of the thermoelastic component can be reflected in the change of the sample thermoelastic response, ie. different intensities of its bending. The potential application of this research can be found within the sensitivity control of Micro-electromechanical systems (MEMS). By illuminating the membranes, they can change their thermoelastic properties, ie. flexibility, and thus the sensitivity of the device itself.