Inversion Channel Research Articles

Geometry Effects of Small MOSFET Devices

The effects of diminishing MOS inversion channel length or width on device characteristics are discussed. As opposed to the geometric device size, an “electric device size” is established by normalizing all dimensions on an appropriately chosen depletion layer width. It is shown how this “electric size” governs the intensity of geometry effects. DC device modeling methods are reviewed with respect to their ease of application to electrically small devices. Finally, means for reduction of geometry effects are considered.

New mobility-measurement technique on inverted semiconductor surfaces near the conduction threshold

A new experimental technique has been demonstrated which has a sensitivity of ${10}^{8}$ electrons/${\mathrm{cm}}^{2}$ in a semiconductor surface inversion channel. Combined with surface-conductivity measurements, the electron (or hole) conductivity mobility can be determined unambiguously near the conduction threshold, which is not possible by previous measurement methods of conductance or transconductance versus perpendicular surface electric field (or gate voltage). The new technique measures the input admittance or impedance of the surface channel and interprets the result by a distributed-transmission-line model. The distributed capacitance element associated with the inversion layer electrons is a direct measure of the inversion electron density, ${C}_{N}=\frac{{q}^{2}{N}_{\mathrm{INV}}}{{k}_{B}T}$. Electron mobilities in the $n$-type surface inversion layers on $p$-type silicon with high and low densities of oxide charge scattering centers have been measured down to ${10}^{8}$ electrons/${\mathrm{cm}}^{2}$. A monotonic mobility decrease with decreasing electron densities has been observed in contrast to previous published data which showed unexplained mobility peaks near the conduction threshold.

Quantum oscillations in an inversion layer on p-PbTe

We report the observation of a variable density inversion layer on p-PbTe. The carriers in the inversion channel are found to have a mobility on the order of 250,000 cm 2 V -1 sec -1. Shubnikov-de Haas oscillations in the channel conductivity were measured in magnetic fields up to 6 T. From the observed periodicity we conclude that the oscillations represent only a fraction of the total number of electrons in the channel.

Study of the Size Quantization in p‐Type Silicon Inversion Layers by Means of Magnetoresistance

AbstractThe Hall‐mobility and transverse magnetoresistance (MR) in p‐type inversion channels on (100) and (111) surfaces of silicon are investigated as functions of the strength and direction of magnetic field and the carrier density Γp at 4.2, 77, and 295 K. A characteristic peculiarity of the obtained results is a considerable MR anisotropy: a magnetic field oriented in the plane of the channel causes a minimum MR. The evaluation of the energetic positions of quantum levels is made to analyze the experiment, two types of holes and nonparabolicity of the band are taken into account. Results of the calculation and the observed MR anisotropy permit to conclude that the quantization of the transverse motion of holes in the channel plays an important role at 77 K for all Γp, and at 295 K for high Γp values. Conclusions about the scattering mechanisms of charge carriers are drawn from the analysis of the Γp dependence of MR.

The GaAs inversion-type MIS transistors

The alloying technique for source and drain n + regions and the chemical-vapor-deposited double layer films of Al 2O 3 and SiO 2 were found to be useful for the realization of the inversion channel GaAs MIS transistors. This is because the alloying was carried out at much lower temperature than donor diffusion and the stability was remarkably improved by using the double layer above mentioned. The transistor had an effective mobility of 2240 cm 2/V.sec, and the threshold voltage was controlled by changing the thickness ratio of the two films. The characteristics of the transistor were compared with the theoretical curves which were calculated by considering several limiting factors; bulk charges, a saturation velocity of carriers and series resistances. The fairly good agreement between the two was found. Some discrepancies, recognized in some cases, seemed to be attributable to some unknown parameters in the theory and to influences of interface states.

The effect of irradiation on the carrier mobility in inversion layers of MOS structures

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Scattering mechanisms in inversion channels of MIS structures on silicon

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Scattering of holes of a two-dimensional gas near Germanium surfaces cleaved in liquid Nitrogen

Hall measurements were made to determine the mobility and concentration of holes in the inversion channels near the surfaces of n-type Ge samples cleaved in liquid nitrogen having different donor concentrations. The experimental results obtained agree with the theory of the scattering of a two-dimensional hole gas by Coulomb centres. The comparison of theory and experiment gives reason to the conclusion that the structure of the valence band near the surface immediately after cleavage is essentially different from the structure in the bulk. The dependence of the charge in the surface levels Qss upon the donor concentration in the bulk, Nd, is found to have the form Qss ∼ Nd1/3. [Russian text ignored]

An MOS-oriented investigation of effective mobility theory

An MOS-oriented study is made into effective mobility theory based on the diffuse-scattering surface conduction model. It is exhibited that the constant-field theory is highly inaccurate over a large part of the surface potential region scanned by the inversion channel MOS transistor and that this approximate theory is not a good standard for comparison with experimental data. Isotropic exact-field effective mobility curves are presented in a form which is amenable to experimental verification and for values of the bulk doping and surface potential normally encountered in inversion channel silicon MOS transistors. Experimental p-channel results are presented and compared against theory. Finally, the calculations and results of a study into the anisotropic effects predicted by an extension of the diffuse-scattering model to the elliptical band structure of silicon are reported and detailed.

Optical Absorption Due to Space-Charge-Induced Localized States

A self-consistent model of the space-charge potential in narrow, degenerate accumulation regions at a planar semiconductor interface is constructed and applied to evaluate the binding energies and wave functions of quantized, localized states for motion normal to the interface. The model attributes the space-charge potential entirely to charge trapped in the two-dimensional energy bands associated with the localized states. Expressions are derived for the contributions to the absorption coefficient due to vertical transitions among the two-dimensional bands and due to interband transitions in which either the initial or final state is localized near the interface. The results of numerical calculations are presented for $n$-type accumulation regions in GaAs and at the (100) surface of silicon. Experimental observation of the structure in the absorption coefficient at infrared frequencies appears to be practical, and would provide a direct observation of quantization effects in narrow accumulation or inversion channels at semiconductor surfaces.

Theoretical characteristics of insulated gate field effect devices

One established a theory of the operation of the insulated gate field effect devices. This analysis takes into account, first, the saturation of the velocity of the carriers at high electric field, second the presence of surface states at the dielectric semiconductor interface. Two types of operation are to be considered, either the channel is obtained by diffusion or epitaxial process or the channel is an inversion channel. In the second type the presence of surface states is the most important factor of operation.