Untersuchung der THz-Emission von Silizium in Abhängigkeit von Grenzflächen- und Kristalldefekten

Optical based non-contact measurement techniques are of great importance in semiconductor device characterization. THz emission from optically excited semiconductor interfaces permits the investigation of transport mechanisms and potential barriers at semiconductor interfaces. So far most available studies concentrate on III-V-compounds. Opening up THz emission for new applications in the area of semiconductor device characterization, the usability of THz emission as an analysis tool for low efficient THz emitters like silicon has to be proven as well. This thesis presents basic studies on THz emission from bare silicon surfaces. Within this work special attention will be paid to the sensitivity of THz emission against interface charges and crystal defects. A theoretical study based on the drift-diffusion model suggests that silicon serves as a surface field emitter under excitation with 800 nm. Although THz emission appears to be highly sensitive against surface preparation, the THz signals only partially reflect the sign of the surface potential. This behaviour is currently addressed to the long carrier lifetime in silicon that leads to a stationary background concentration of photocarriers in combination with the high repetition frequency of the laser system and create a non equilibrium surface condition differing from the original surface potential. This makes investigations of silicon interfaces more challenging compared to the investigation of III-V-compounds. The second part of the study concentrates on the detection of crystal defects close to the surface. Ion implantation was used to produce a controlled number of defects within the silicon crystal. Different excitation wavelengths were applied to demonstrate that THz emission is strongly influenced by the damage-induced alteration of electrical properties. Therefore it can be used for the identification of point defects, that are not accessible by using classic methods like Rutherford backscattering.


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