THEORETICAL DETERMINATION OF THE ADMITTANCE OF THE METAL GATE IN A MET~XIDE--SEMICONDUCTOR SYSTEM AND EFFECT OF THE GATE ON FARADAY ROTATION AND ELL IPT IC ITY

We calculate the admittance ofthe metal gate in a metal--oxide-semiconductor system in the Faraday geometry using the Boitzmann transport equation. We find that the value of the admittance calculated from this model agrees well with experimentally determined values. Using this calculated value of the admittance, we find that the contribution of the metal gate to the Faraday rotation and ellipticity to be negligible and hence we may ignore the metal gate altogether xcept for its contribution as a reflecting surface. The inversion layer in a metal-oxide-semiconductor (MOS) system is a subject of much current interest. Following the usual practice of treating the inversion layer as a two-dimensional e ectron gas, we calculated its contribution to free-carrier Faraday rotation and ellipticity [1]. Here we wish to address the question of whether or not the free carriers in the metal will also make a contribution. As in ref. 1, we will ignore multiple reflections in the oxide layer, which were treated elsewhere [2]. Because the metal gate is very thin (20-50 A) it also can be treated as a two-dimensional charge layer. Then, for the purpose of calculating its contribution to free-carrier Faraday rotation or ellipticity, we need to calculate the surface admittance (two-dimensional conductivity) of the metallic charge layer. The usual bulk metal refractive index is not useful in this context but, following Dingle [3], we may define a generalized complex refractive index b