INTERACTION OF 10.6-MICRON LASER RADIATION WITH BULK SILICON.
Research and development technical rept.,
ARMY ELECTRONICS COMMAND FORT MONMOUTH N J
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The conduction process in semiconductors exhibits effects associated with inertia of the free carriers when the frequency of observation is of the order of the reciprocal of the relaxation time for the randomization of the momenta of the carriers. Since these effects can cause significant changes in the conductivity, permittivity, and attenuation constant in silicon, and since the principal parameter determining these changes is the free carrier relaxation time t, it is necessary that an accurate value of t can be determined. When one examines different experimental data reported in the literature and deduces the value of t for silicon from these different sources, a basic discrepancy is found between the value of t for 10.6 micrometers and at microwave frequencies. The present paper derives the equations which account for the dependence of semiconductor parameters on free carrier bipolar relaxation time using a simple classical model. The experimental method for determining an accurate value of the bipolar relaxation time t for reasonably pure silicon is described. The experimental results give a value of t 1.8 x 10 to the -14th power sec. This value is a factor of 112 smaller than that obtained from the experiments of others at microwave frequencies. One can conclude from the above if the classical model used is valid at 10.6 micrometers that t decreases with wavelength between 12,500 micrometers and 10.6 micrometers. Alternately, if one assumes that t is not a function of wavelength which is the case for at least 12,500 micrometers and 10.6 micrometers then it is evident from the anomaly in t that a classical model for free carrier absorption is inadequate. Author
- Lasers and Masers
- Solid State Physics