Silicon Metal Oxide Semiconductor Field-effect Transistors Research Articles

Electron power loss in the (100) n channel of a Si metal-oxide-semiconductor field-effect transistor. I. Intrasubband phonon scattering

The electron energy relaxation is studied as a function of the ‘‘electron temperature’’ Te in the n channel of a (100) surface silicon MOSFET (metal-oxide-semiconductor field-effect transistor) device by inspecting the phenomenological energy relaxation time τε(Te) at 4.2 °K, 77 °K, and 300 °K lattice temperatures. τε is theoretically calculated in order to determine the relative contributions of shear horizontal (SH), pressure-shear vertical (P-SV), shear vertical-pressure (SV-P), total reflection shear vertical pressure (TR), and Rayleigh (R) surface acoustic phonon modes to the electron energy relaxation at the interface. Two-dimensional electron transport is assumed and the effects of subbanding near the interface are included. Only electron scatter events within subbands are studied (intrasubband). This exhaustive study finds that surface modes do not dominate the electron energy relaxation at the Si–SiO2 interface at TL =4.2 °K. Some other mechanism(s) must predominate at TL =4.2 °K.

Electron power loss in the (100) n channel of a Si metal-oxide-semiconductor field-effect transistor. II. Intersubband phonon scattering

A simple matrix element is used to approximate electron-acoustic phonon scattering between different electron subbands i in the n channel of a (100) surface silicon MOSFET (metal-oxide-semiconductor field-effect transistor) device. This matrix element is used to determine the form of the electron power loss Pij in a i→j intersubband transition. P10 is calculated for TL =4.2 °K lattice temperature and electron temperatures Te between 4.4 °K and 18 °K when the electron inversion density Ninv =(3.76–10.0)×1011 cm−2 and an acceptor density NA =1014/cm3, and compared to Fang and Fowler’s experimental data (which is put into the form of an experimental power loss Pexp). This is justified since the total power loss P due to intrasubband scattering as well as other Pij terms besides P10 is small. It is found that good to excellent fits between P10 and Pexp occur by adjusting the separation Δε10 between the lowest two circular subband edges. Δε10 is between 5.2 and 9.4 meV, and the electron-phonon deformation coupling constant D≊3.5 eV. The values of Δε10 obtained in such a manner roughly agree with Stern’s theoretical self-consistent results. P10 is very sensitive to both Δε10 and to the effective mass for motion parallel to the surface m1 with the results implying that m1≊0.19m0 (m0=free electron rest mass). If one wants to find the contribution of intersubband scattering to P at higher TL, the formalism should still be applicable, although the approach could be much more complicated due to the addition of new Pij terms coming from both higher subbands and new scattering agents such as optical modes.

Degeneracy effects on semiconductor surfaces

Two types of degeneracy effects are discussed in this paper. In the first case, degenerate surfaces on degenerate bulk semiconducting materials are reviewed. It is pointed out that epitaxic thin films are a prerequisite for any reasonable study of this type of substance. Recent work on degenerate lead chalcogenide films have illustrated the need for epitaxic films. The results show that the scattering at the surface is quite specular. Extremely high surface charge densities were generated by oxygen adsorption. It was found that coulombic interactions caused spreading of the surface state levels comparable to the band gap of the semiconductors. A model based on an oxide with high defect densities of ionized oxygen appears more reasonable. In the second case, a degenerate layer is formed on a nondegenerate bulk by means of an external electric field in a metal-oxide-semiconductor field effect transistor (MOSFET) structure. At low temperatures, an n-type inversion layer formed on a (100) p-type silicon MOSFET behaves like a two-dimensional electron gas as shown by Fowler, Fang, Howard and Stiles using Schubnikov-de Hass osculations. Recently, an oscillatory behavior was observed in the gate voltage dependence of the capacitance of a MOSFET in a high magnetic field (> 50 kOe). Potential utility of these measurements is discussed.