Effect of reverse substrate bias on the minigap in Si inversion layers

The influence of a reverse substrate bias on the minigap of Si inversion layers on (10, 1, 1) and (8, 1, 1) surfaces has been investigated. Substrate bias shifts the position of the gap to higher gate voltages but the center of the gap remains at a fixed mobile charge density. Reverse bias increases the magnitude of the minigap by as much as 30%.     

Temperature dependence of effective mobility edge and inelastic scattering time in silicon MOS inversion layers in strong magnetic fields

Temperature (T) dependence on Hall conductivity (σ_xy) in Si MOS inversion layers measured in 15 T at T=1.4?10 K is investigated by comparing dσ_xy/dN_s, N_s electron concentration, to the calculation based on an effective mobility edge (E_c) model. Temperature dependence of inelastic scattering time is discussed in connection to the T-dependence of E_c.     

Dependence on substrate bias of the effective mass and dingle temperature of electrons in the surface inversion layer of silicon

The amplitude of the quantum oscillations in the magnetoconductance of a silicon inversion layer has been studied as a function of gate voltage V_g, for different values of the temperature T, applied magnetic field strength H and substrate bias V_s. By analyzing the amplitude of the oscillations at fixed V_g and V_g as a function of T and H, the dependence of the cyclotron effective mass m¹ and the Dingle temperature T_D on V_g and V_s can be obtained. The dependence of m¹ on V_g for different values of V_s is compared with the prediction of theory.     

Effect of neutral scatterers on electron mobility in silicon (100) inversion layers

The electron mobility inn-type inversion layers at (100) silicon surface is studied at low temperature. Using the lowest subband calculated numerically, and taking into account the neutral impurity distribution in the vicinity of the Si–SiO₂ interface, the process of carrier scattering is investigated by the Green's function formalism. Experimental data for electron mobility are in good agreement with the results from Dyson's equation in Born approximation in the case of shallow and steep profiles of impurities.     

Self-consistent calculation of impurity scattering in inversion layers

The local density-functional method has been applied to the calculation of the influence of an ionized impurity on the electrons in an inversion layer on the surface of silicon. Compared to linear screening theories this theory shows improved agreement with experiments on the mobility. The bound state associated with the self-consistent potential has a very small binding energy.     

Remote polar phonon scattering in silicon inversion layers

A new scattering mechanism for free carriers in inversion layers is proposed. It is shown that polar optical phonons of the insulator couple effectively to the inversion layer electrons in the adjacent semiconductor. For the Si-SiO₂ interface this scattering by remote polar phonons influences substantially the field dependent mobility of the silicon inversion layer carriers.     

Anisotropic impurity scattering in electrically quantized inversion layers

The Boltzmann Equation is solved for a two dimensional gas of charge carriers in order to calculate the conductivity of field-effect transistors. The charge carriers are assumed to be scattered by point charges. The scattering process is treated in Born approximation. The resulting conductivity tensor is in apparent disagreement with experimental results.     

First order intervalley scattering in silicon inversion layers

The mobility limited by first order intervalley scattering in a quantized silicon inversion layer is calculated by an iterative solution of the Boltzmann equation incorporating both scattering-out and scattering-in terms. The mobility values are found to be much smaller than those based on a relaxation-time model considering scattering-out only.     

Determination of the g-factor of electrons in N-type silicon surface inversion layers

The g-factor of conduction electrons in the surface inversion layer on a silicon (100) surface has been determined using the tilted magnetic field method developed by Fang and Stiles.The value of (m¹/m₀)·g at the fixed magnetic field was independent of surface carrier density n_s, whereas it had a sharp peak at about 97 koe. At strong magnetic field limit the value was constant and 0.4. If we take the effective mass of conduction electrons in the inversion layer on the (100) surface as 0.2m₀, the g-factor is about two which is the same as that for conduction electrons in bulk silicon.     

Frequency dependence of cyclotron resonance in si inversion layers in the region of activated conductivity

Cyclotron resonance of electrons in a Si MOSFET has been studied at a number of far infrared laser frequencies and at surface electron densities down to 3 × 10 cm^?2 in the activated conductivity regime. The scattering rate exhibits $\text{B}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ behavior for ωτ > 2 as in the metallic regime. Effective masses obtained from the fits are found to increase with decreasing density at frequencies $\text{V}\text{?}\text{? 25}\text{cm}{}^{\mathrm{?1}}$. It is possible that this continued evidence of metallic-like behavior is due to the fact that the photon energy is larger than the DC activation energy at these densities.     

On the absorption of infrared radiation by electrons in semiconductor inversion layers

Resonances in the inversion layer for infrared fields normal to the interface do not occur at the electric subband splittings. They are shifted from the subband splittings by resonant screening of the infrared field. The corrections for (100) Si surfaces are shown to be comparable to the shifts ascribed to many-body effects.     

Optical and intervalley scattering in quantized inversion layers in semiconductors

The momentum relaxation time for scattering of electrons in quantized levels of an inversion layer on a semiconductor surface is calculated for interactions via optical and intervalley phonons. A selection rule is found which prohibits transitions between subbands belonging to the same valley or set of valleys, at least in the zero order to which these scattering processes may occur. Relaxation times for the zero-order interaction and the first-order interaction are obtained for intervalley phonons. The results are applied to the case of a (100)-silicon surface, with electrons in the three lowest subbands (with energy levels E₀, E₁, E'₀) of the two sets of valleys. Agreement with the experimental data of Fang and Fowler is good when the combined effects of intervalley and acoustic scattering are considered.     

Studies of electron screening effects on the electron mobility in silicon surface inversion layers

Theoretical calculations of the effects of electron screening of the randomly distributed oxide charges on the electron mobility in surface inversion layers at 4.2 K show that screening substantially enhances the mobility even in weakly inverted surface layer. Surface conductances are measured at 4.2 and 77 K on n-channel MOS transistors with 4 × 10¹¹ ions/cm². Threshold voltages are obtained by matching the inversion layer conductance versus gate voltage data to the theory. The observed mobility magnitude at 4.2 K is about 2000 cm²/V-s which is in excellent agreement with the theory including screening but without adjustable parameters. A conductance tail of several volts wide below the theoretical threshold voltage and a large positive threshold voltage shift are observed at low temperatures which are attributed to an areal inhomogeneous distribution of fast surface states near the silicon conduction band edge.     

Remote polar phonon scattering for hot electrons in Si-inversion layers

The effect of the remote interfacial phonon (R.I.P.) scattering on the carrier drift velocity v is evaluated in function of the effective mobility, i.e. in function of the surface roughness. A perturbation theory using the experimental ν?F relation as a zero order approximation is used to calculate the contribution of the R.I.P. scattering. The calculation shows that the influence of this phonon mode scattering on the transport properties in Si-inversion layers is dependent on the carrier low field mobility and is of the order of 10%. The R.I.P. scattering is particularly significant in the warm electron regime, having no consequence on the saturation velocity.     

Low-density spin susceptibility and effective mass of mobile electrons in Si inversion layers

We studied the Shubnikov-de Haas (SdH) oscillations in high-mobility Si-MOS samples over a wide range of carrier densities n approximately (1-50)x10(11) cm(-2), which includes the vicinity of the apparent metal-insulator transition in two dimensions (2D MIT). Using a novel technique of measuring the SdH oscillations in superimposed and independently controlled parallel and perpendicular magnetic fields, we determined the spin susceptibility chi(*), the effective mass m(*), and the g(*) factor for mobile electrons. These quantities increase gradually with decreasing density; near the 2D MIT, we observed enhancement of chi(*) by a factor of approximately 4.7.     

Monte Carlo simulation of two-dimensional hot electrons in n-type Si inversion layers

Monte Carlo simulation is carried out to study high field transport of the two-dimensional electron gas formed on the (100) surface of silicon. Good agreement is obtained between the measured and calculated results. The saturation of the drift velocity is found to depend on the magnitude of the first-order intervalley phonon scattering.     

On the role of scattering by surface roughness in silicon inversion layers

Experimental results are presented, which strongly suggest that scattering of carriers by surface roughness may be important in the silicon inversion layer of metal-oxide-semiconductor structures. Low temperature data for p-type channels on identical orientation at high surface field show that mobility results in this region are dependent only on the mode of sample preparation and are independent of surface charges. The most reasonable explanation for these observations is offered by a scattering mechanism which is closely associated with the surface condition of the SiSiO₂ interface, namely, scattering by surface roughness. This scattering is a direct result of the fluctuating potential caused by the imperfect interface which is only a small distance from the inversion carriers. A calculation of the effect of surface roughness on surface carrier mobility is also given and found to be in satisfactory agreement with the experimental results. The application of the theory to the observed results permits an estimate to be made of the physical dimensions of the surface roughness of the Si-SiO₂ interface.     

Evidence for mobility domains in (100) silicon inversion layers

In proof of the existence of domains with different mobilities measurements of Shubnikov-de Haas oscillations, piezoresistance, and transverse “Hall” field due to mobility anisotropy are provided. The energy splitting between the ground state subbands of different valleys has been determined.