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 indi...cators 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.
Faculty:
University of Niš, Faculty of Electronic Engineering
