Electron transport properties of quantized silicon carbide inversion layers

Electron transport properties in SiC quantized inversion layers have been studied by means of a Monte Carlo procedure. It has been observed that the contribution of polar-optical phonon scattering produces a significant influence of the effective-electric field on the high longitudinal field transport regime, this being the main difference of SiC with respect to standard Si inversion layers. The energy- and momentum-relaxation times have been calculated and the results suggest that electron velocity overshoot effects are less important than in Si metal-oxide semiconductor field effect transistors. The electron mobility is not very different from their silicon counterparts, but the saturation velocity is higher.     

Vacancy model of micropipe annihilation in epitaxial silicon carbide layers

Kinetic processes of annihilation (healing) of a micropipe threading into a growing layer from a substrate-seed are considered in terms of the vacancy model of heteropolytype epitaxy of silicon carbide we previously suggested (Fiz. Tekh. Poluprovodn., 39, 296 (2005); 41, 641 (2007)). A relationship is found between the growth rate of an epitaxial film, vacancy lifetime, and defect layer width at which the micropipe is healed. Both kinds of vacancies, of carbon and silicon type, are taken into account. In addition, a simplified linear model of the process of micropipe healing is suggested. The relationship between the micropipe diameter r ₀ and the defect layer width l* is determined in terms of this model: l* = r ₀(G/g), where G is the layer growth rate and g is the vacancy velocity, which yields l* ≈ 6r ₀ for actual growth conditions.     

Observation of velocity overshoot in silicon inversion layers

Employing a test structure, velocity overshoot in silicon inversion layers is observed at room temperature. For channel lengths longer than 0.3 μm, the velocity/field relation follows the well-known behavior with no channel length dependence. The first indication of velocity overshoot is seen at a channel length of 0.22 μm, while at L=0.12 μm, drift velocities up to 35% larger than the long-channel value are measured     

Velocity of surface carriers in inversion layers on silicon

Velocity-field curves for surface free-carriers in silicon are determined from measurements on resistivegate IGFETs. The measurements were performed on n-channel devices fabricated on both (100) and (111) substrates and on p-channel devices fabricated on (100) substrates. The channel length of the devices is ～8 μm and the impurity concentration of the substrates is ～ 10¹⁵ cm^?3. The dependence of velocity on the field strength along the channel is found to be well approximated by an empirical relationship involving three parameters: low-field mobility μ₀, a critical field $\text{E}{}_{\mathrm{cy}}$ signalling the onset of velocity saturation, and a parameter α that determines the curvature between the constant-mobility and constant-velocity branches of the curve. The curve-fitting parameters are given in tabular form for the two n-channel and one p-channel systems studied. The dependence of the velocity-field curves on temperatures in the range 100–350K is also reported.     

Influence of oxygen on the ion-beam synthesis of silicon carbide buried layers in silicon

The properties of silicon structures with silicon carbide (SiC) buried layers produced by high-dose carbon implantation followed by a high-temperature anneal are investigated by Raman and infrared spectroscopy. The influence of the coimplantation of oxygen on the features of SiC buried layer formation is also studied. It is shown that in identical implantation and post-implantation annealing regimes a SiC buried layer forms more efficiently in CZ Si wafers or in Si (CZ or FZ) subjected to the coimplantation of oxygen. Thus, oxygen promotes SiC layer formation as a result of the formation of SiO_x precipitates and accommodation of the volume change in the region where the SiC phase forms. Carbon segregation and the formation of an amorphous carbon film on the SiC grain boundaries are also discovered. Fiz. Tekh. Poluprovodn. 32, 1414–1419 (December 1998)     

Surface charges and surface potential in silicon surface inversion layers

The effect of interface charges on the channel conductance in MOS transistors has been investigated. It has been found that, by measuring the conductance as a function of temperature, it is possible to determine both the "fixed" interface charge which is independent of the surface potential and the charge trapped in surface states whose occupancy is a function of the surface potential. The characteristics of the two charge components are discussed. It appears that neither a continuous nor a delta-function energy distribution alone is adequate to describe the observed surface-state density.     

Determination of interface-state density and mobility ratio in silicon surface inversion layers

A method has been proposed to deduce the energy distribution of interface states and the mobility ratio of carriers simultaneously from Hall effect measurements at two different temperatures. Using this method, the interface-state density Nssand the mobility ratiorof carriers were determined on both n-channel and p-channel silicon MOS transistors. The result indicates that Nssdetermined in this method is very small near the center of the energy gap and increases as the energy of the states approaches the band edges. The interface-state density inside the conduction and the valence band was found as high as 10¹³cm^-2eV^-1. The value of mobility ratio was found to depend both on temperature and surface-carrier density. Increase of mobility ratio with decreasing carrier density was observed in all samples, it is interpreted as due to diffuse scattering and to Coulomb scattering by localized interface charges.     

Electron velocity overshoot at room and liquid nitrogentemperatures in silicon inversion layers

Effective electron velocities in silicon MOSFETs exceeding the bulk saturation values of 10⁷ cm/s at room temperature and 1.3×10⁷ cm/s at liquid-nitrogen temperature are inferred. This conclusion suggests that electron velocity overshoot occurs over a large portion of the device channel length. To infer this phenomenon, submicrometer-channel-length Si MOSFETs with lightly doped inversion layers were fabricated. These devices have low field mobility of 450 cm²/V-s and showed only slight short-channel effects. Effective carrier velocities are calculated from the saturated transconductance g_m at V_DS=1.5 V after correction for parasitic resistances of source and drain     

Electron and hole mobilities in inversion layers on thermally oxidized silicon surfaces

Extensive measurements of electron and hole mobilities in inversion layers on thermally oxidized silicon surfaces were performed using the field effect conductance technique. It was found that both electron and hole mobilities are practically constant and approximately equal to one half of their respective bulk values up to a surface field of about 1.5 × 10⁵volts/cm, corresponding to about 10¹²electronic charges/cm²induced in the silicon. At higher fields the inversion layer mobilities begin to decrease slightly. The temperature dependence of inversion layer mobilities follows a T^-1.5rule at the upper range of the interval -196 to 200°C, indicating a scattering mechanism similar to lattice scattering. This observation is further supported by the lack of a significant effect of an order-of-magnitude variation in the bulk impurity concentration (10¹⁵- 10¹⁶cm³) on the inversion layer mobilities. No significant effect of structural and geometrical parameters (such as channel length and shape, oxide type and thickness, and surface charge density) was found on the inversion layer mobilities.     

Semi-insulating silicon carbide layers obtained by diffusion of vanadium into porous 4H-SiC

Semiconductors - Semi-insulating silicon carbide layers have been obtained by diffusion of vanadium into porous 4H-SiC. The diffusion was performed from a film deposited by cosputtering of silicon...     

Influence of the interface-state density on the electron mobility in silicon inversion layers

The electron inversion-layer mobility in a metal oxide semiconductor field effect transistor, as a function of the transverse electric field, has been studied in the temperature range 13–300K for different interface-state densities. Experimental data are in excellent agreement with a simple semi-empirical model. However, the term attributed by other authors to phonon scattering depends on the interface-state density, even at high temperatures, and becomes negative at low temperatures. These facts are shown to be a consequence of the dependence of coulomb scattering on the transverse electric field.     

Measurement of the high-field drift velocity of electrons in inversion layers on silicon

A new technique is described for the study of high-field transport along semiconductor interfaces. The technique involves observation of the time-of-flight of a packet of carriers across a region of uniform tangential electric field at the semiconductor surface. We use the technique to measure the drift velocity of electrons along the Si-SiO2interface for tangential fields in the range 2.5-4.0 kV/cm. Drift velocities as high as 8.5 × 10⁶cm/s are observed; these values are almost 40% higher than previously reported in the literature.     

Negative differential resistance in (100) n-channel silicon inversion layers

A voltage controlled negative differential resistance (NDR) in n-channel MOSFETs of (100) orientation is investigated for lattice temperatures between 1.5 and 100 K in transverse magnetic fields up to 7 Tesla. By variation of the length of the pulses and by investigating samples of different geometry it is shown, that the NDR is not caused by lattice heating. Position and magnitude of the NDR depend substantially on the magnetic field. The observed effects can be explained by cooling of the hot carriers by the magnetic field.     

Compact models for silicon carbide power devices

Compact silicon carbide (SiC) power semiconductor device models for circuit simulation have been developed for power Schottky, merged-PiN-Schottky, PiN diodes, and MOSFETs. In these models, the static and dynamic performance of the power SiC devices requires specific attention to the low-doped, voltage blocking drift region; the channel transconductance in MOS devices; the relatively low-intrinsic carrier concentration; the incomplete ionization of dopants; and the temperature dependent material properties. The modeling techniques required to account for each of these characteristics are described.     

Amorphous silicon/silicon carbide superlattice avalanchephotodiodes

An a-Si/SiC:H superlattice avalanche photodiode (SAPD) has been successfully fabricated on an ITO/glass substrate by plasma-enhanced chemical vapor deposition. The room-temperature electron and hole impact ionization rates, α and β, have been determined for the a-Si/SiC:H superlattice structure by photocurrent multiplication measurements. The ratio α/β is 6.5 at a maximum electric field of 2.08×10⁵ V/cm. Avalanche multiplications in the superlattice layer yields an optical gain of 184 at a reverse bias V_R=20 V and an incident light power P_in=5 μW. An LED-SAPD photocouple exhibited a switching time of 4.5 μs at a load resistance R-1.8 kΩ     

Formation of graphene layers by vacuum sublimation of silicon carbide using a scanning heat source

The kinetics of surface graphitization during dissociative vacuum evaporation of silicon carbide, under the effect of a scanning heat source, is studied. A model of the process is developed. The model provides a means for theoretically treating the dynamics of formation and the number of residual carbon atomic layers. The vapor stoichiometric coefficient which ensures the minimization of the number of structural defects in graphene, is optimized at the sublimation temperature: θ = 1/η(T _max). The proposed method can be used as a basis for graphene production technology.     

Fullband quantization analysis reveals a third valley in [001] silicon inversion layers

This letter presents calculations of the silicon two-dimensional (2-D) band structure obtained by accounting for the fullband energy dispersion of the three-dimensional silicon crystal, as derived from the non-local-pseudopotential method. The most interesting result is the identification of a third valley for the 2-D electron gas in the [001] quantization direction, besides the two families of subbands (the unprimed and primed ones) universally considered according to the effective mass approximation.     

Photoluminescence of anodized silicon carbide

The luminescence of single-crystalline 6H-SiC plates after electrochemical etching has been investigated. The photoluminescence spectrum was found to change strongly after etching; the decay times of separate bands were determined. Just as in the case of silicon, the change in the photoluminescence could be due to the formation of nanostructures. Fiz. Tekh. Poluprovodn. 31, 315–317 (February 1997)     

Thermal noise in inversion layers

Experiments on uniform channel (V_DS ≈ 0) MOSEFTs with resistance R_DS show that the thermal noise is given by the normal Nyquist formula $\text{v}{}_{\mathrm{n}}{}^2\text{= 4}\text{kT}\text{R}{}_{\mathrm{DS}}\text{Δf}$. The modification to this formula which has been proposed is thus not necessary. The discrepancies are discussed.