Comparison between optical and electrophysical data on free electron concentration in n-InAs samples

A theoretical model has been developed for determining free electron concentration in n-InAs from characteristic points in far infrared region of reflection spectra. We show that when determining free electron concentration one should take into account the plasmon-phonon coupling, otherwise free electron concentration will be overestimated. We have calculated electron concentration, N_opt, as a function of characteristic wave number, ν₊, which is described by a third order polynomial. 
Twenty one n-InAs samples (5-doped with tin and 16-doped with sulfur) have been tested at room temperature for electron concentration using two methods, i.e., the conventional four-probe (Van der Pau) method (N_Hall) and the optical method developed by us (N_opt). The reflective surfaces of investigated samples were processed either with chemical-mechanical polishing or treating with short-grained abrasive powder.  
It was shown that for all the investigated samples the condition N_opt > N_Hall was relevant. The difference between optical and electrophysical electron concentration values has been shown to be greater in case of chemically polished reflective surface of the sample and smaller in case of abrasive-treated one. 
The experimental results have been compared with the same data previously obtained for n-GaAs samples. Qualitative model has been suggested to explain obtained experimental data. 

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