Photothermal Deflection Phenomenon Of Semiconductors With Setp Optical Excitation

The photothermal deflection (PTD) technique, which is developed from the photothermal effect, is a kind of nondestructive detecting technique. Because of some advantages such as high sensitivity, sample-non-pretreatment and non-contact measurement, the PTD technique has been widely applied to the area of physics and material sciences etc.. Recently, J. Zhao and S. Zeng advances a new PTD technology, namely PTD technique with step optical excitation, and a preliminary experimental and theoretical research is also performed.Compared with the traditional PTD method, the PTD technique with step optical excitation has many advantages such as simpler equipment, easier adjustment and faster measurement.The PTD technique with step optical excitation is currently in a stage of development. Previous studies are only limited to the photothermal effect of general solid material, and most of the measurements are restricted to the characterization of thermal parameters of materials. In our recent studies, different characteristics of photothermal signals with step optical excitation between semiconductor materials and generally solid materials are discovered, which provides the possibility of characterizing semiconductor parameters using step optical excitation. In this paper, the semiconductor photoluminescence processes, generation mechanism of heat source and acousto-optic and photoehrmal effects in semiconductor are reviewed, and our main theoretical and experimental research works about the PTD technique is listed as follows:1. According to the principles of photoelectric effect of semiconductor materials and heat transfer, an one-dimensional theoretical model of the temperature variation in semiconductor materials with the step optical excitation is presented, which is also solved by using eigenfunction expansion method. The temperature changes of semiconductor with step optical excitation are studied through numerical simulations, and the influences of different minority carriers life time and thermal diffusivities of the semiconductor on temperature changes are investigated. In addition, the relationship between the temperature changes of semiconductor and the corresponding PTD signals is analyzed.2. The experiment system about the PTD technique with step optical excitation is established, and the light path and signal acquisition part of the system are analyzed. Adjusting device of the excitation light and detecting light, sample platform and devices of receiving signal are introduced. Moreover, the adjustment method of position detectors, detection beam and sample surface level are also presented.3. The PTD signals of the semiconductor samples with different minority carriers life time are studied by the PTD experimental system with step optical excitation. The observed experimental results are in agreement with the numerical results, which show that semiconductor parameters can be characterized by photothermal techniques with step optical excitation. In addition, the relationships between the PTD signals and the distance between the probe beam and the sample surface, as well as the distance between the probe beam and the pump beam are analyzed.