The Mobility of Minority Carriers within the Surface Region of MOS Devices

The behavior of the minority carrier mobility in the silicon bulk as well as in the MOS inversion layer at the Si/SiO2 interface has been investigated experimentally. The well known MOS inversion layer mobility of charge carriers in silicon amounts to approximately one half of the bulk value usually without any distinction between majority and minority carriers. For an accurate comparison the bulk values of minority carrier mobility have been evaluated by Shockley-Haynes experiments on MOS structures in accumulation^2],3], yielding good agreement with D.B.M.Klaassen´s model^1]. Additionally, reliable values of the surface mobility have been evaluated with the aid of quantum-Hall-effect structures^4]. As the preponderant influence on Coulomb scattering the parasitic surface charge of interface states and oxide charge are introduced. Although their influence is smaller compared to that of dopant impurities, by a factor 8..20, they dominate the temperature behavior of the inversion layer mobility for values Nax + Nss ¿ 10¹⁰cm^-2. Thus the measured temperature behavior of the inversion layer mobility can be desribed by applying Klaassen´s model^1] with an equivalent doping concentration comprising parasitic surface and oxide charges as well as bulk impurities.