Raman measurements are reported of collective modes (plasmons) and single-particle excitations in modulation-doped $\mathrm{Ga}\frac{\mathrm{As}}{{\mathrm{Al}}_x}{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum-well systems as a function of the wave-vector component $k_{\parallel }$ parallel to the electron layers. Samples with five layers show discrete layer-plasmon modes manifesting the coupling of the electrons in different layers by Coulomb interaction. The Raman spectra due to single-particle excitations are narrow bands peaking at $\overline{h}{k}_{\parallel }{v}_{\mathrm{F}}^{2\mathrm{D}}$ characteristic for the response of a 2D electron gas.

Here a physically based channel mobility model has been developed to investigate the temperature dependence of the field-effect mobility of $4H\text{-}\mathrm{Si}\mathrm{C}$ metal-oxide-semiconductor (MOS) transistors with thermally oxidized gate insulators. This model has been designed so that it accounts for the high density of traps at the MOS interface. This temperature dependence is a key issue for silicon carbide electronics, as its basic material properties make it the foremost semiconductor for high power/high temperature electronic devices in applications such as spacecraft, aircraft, automobile, and energy distribution. Our modeling suggests that the high density of charged acceptor interface traps, encountered in thermally grown gate oxides, modulates the channel mobility due to the Coulomb scattering of free carriers in the inversion layer. When the temperature increases, the field-effect mobility of these devices also increases, due to an increase in inversion charge and a reduction of the trapped charge. Experimental data of the field-effect mobility temperature dependence are in good agreement with this model.