Microwave hot electron effects in semiconductor quantized inversion layers

Hot electron microwave conductivity of quantized inversion layers in semiconductor surfaces has been calculated based on a displaced Maxwellian approximation for the electron distribution function. The calculations performed take into account repopulation of carriers among the various subbands. The effects of the energy, momentum and intervalley population exchange rates due to scattering by acoustical and intervalley phonons are included in the derivations. The results are applied to silicon where the electron energy and momentum losses by intervalley phonons in both the zero-order coupled and first-order coupled cases are important. Numerical computations for the microwave conductivity of silicon are presented as a function of bias electric field and frequency. It is found that significant changes in the conductivity contribution for a fixed bias field occur at frequencies on the order of the intervalley repopulation rate. Though no experimental work in this frequency range has been performed, it should be easily observable.     

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.     

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.     

Fluctuations and noise of hot carriers in semiconductor materialsand devices

After recalling the definition of the noise temperature, the macroscopic expressions for noise sources are shown not to be specific to the hot carrier regime, though dependent on the electric field strength. Careful modeling allows one to obtain important information on transport parameters from noise measurements. The microscopic noise source expressions, via the transition rates, give a unified view of the noise sources. In particular, it is clarified that noise sources are intercorrelated, and that there is also space correlations over lengths of a few mean free paths. Recent developments are reviewed, concerning noise modeling using direct numerical methods for solution of the Boltzmann equation. Finally, impedance field methods for modeling noise of devices are briefly evoked     

Harmonic generation due to hot electrons in surface inversion layers

Harmonic generation due to hot electron nonlinearity in Si-inversion layers at 77 K in the presence of a large high frequency signal is studied on a drifted Maxwellian model. The third harmonic content increases with increase in field amplitude but decreases to negligible values for frequencies of about 1000 GHz.     

Transport of hot charge carriers in Si,GaAs, InGaAs,and GaN submicrometer semiconductor structures with nanometer-scale clusters of radiation-induced defects

The distributions of the radii of subclusters of radiation-induced defects and of the distances between the cores of these subclusters are calculated for Si, GaAs, and GaN. The features of the transport of hot charge carriers in the above materials upon irradiation with neutrons are discussed. A burst in the velocity of electrons in Si, GaAs, InGaAs, and GaN before and after irradiation is calculated for the first time; also, the extent of manifestation of the above effect in different semiconductor materials is compared.     

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.     

Simulation of drift-diffusion transport of charge carriers in semiconductor layers with a fractal structure in an alternating electric field

Based on the fractional-order partial differential equation, the diffusion-drift charge-carrier transport in a semiconductor layer with a fractal structure under a longitudinal alternating electric field is simulated. The simulation showed that the space–time distributions of carriers are broadened and asymmetric in layers with a fractal structure. Under certain conditions, the effect of charge oscillation frequency doubling in an external alternating electric field is observed.     

Distribution of charge carriers in dissipative semiconductor structures

It was experimentally shown that redistribution of the charge-carrier concentration occurred in nonequilibrium electron-hole plasma during formation and excitation of the dissipative structure by a strong electric field in the bulk of Te and InSb single crystals. In this case, if there are only longitudinal autosolitons in the dissipative structure, the carrier concentration decreases outside the autosolitons. The charge-carrier concentration increases outside autosolitons if the transverse autosolitons are present. It is suggested that the longitudinal autosolitons formed in the nonequilibrium electron-hole plasma developed by the Joule heating are “cold” and the transverse autosolitons are “hot”.     

Temperature delocalization of charge carriers in semiconductor lasers

The temperature dependences of emission characteristics are investigated for laser diodes based on asymmetric separate-confinement heterostructures with a broadened waveguide. It is established that an increase in the charge-carrier concentration in the waveguide layer is the basic mechanism of saturation in the light-current characteristic with increasing temperature in the CW mode. It is experimentally shown that the temperature delocalization of charge carriers leads to increasing internal optical losses and decreasing external differential quantum efficiency. It is shown that the degree of delocalization of charge carriers depends on the charge-carrier temperature distribution, the threshold concentration, and the quantum-well depth. The effect of thickness and energy depth of the quantum well on the temperature sensitivity of the threshold current and output optical power is considered.     

Model-free determination of the dependence of charge density in accumulation and inversion semiconductor layers on the semiconductor surface potential from the voltage-capacitance characteristics of metal-insulator-semiconductor structures

A method for the analysis of the quasi-static voltage-capacitance characteristics of metal-insulator-semiconductor structures in the majority-carrier depletion region of the semiconductor surface is developed. The method provides for the quantitative evaluation of the doping concentration, the flat-band voltage, and the effective values of the capacitance and thickness of the gate insulator. The dependences of the surface potential and surface charge in the semiconductor on the gate-electrode potential are obtained in the absence of a priori data on the state of the electron gas during high enrichment or strong inversion. It is shown that these experimental dependences can be used as a criterion for the validity of the theory of the space-charge region in a semiconductor when the effects of degeneracy and dimensional quantization of electron gas are considered.     

Electromagnetic radiation from hot carriers in FET-devices

We report on the emission of light from si MOS and GaAs MES devices. Processes involving band-to-band transitions and a Bremsstrahlung-continuum below the band-gap are shown to exist. Spatially nonuniform emission from the MESFETs is observed. The GaAs results are compared with Monte Carlo simulations.     

Average mobilities of carriers in subdoped silicon layers

The average mobilities of carriers in subdoped silicon layers as a function of surface as well as background concentrations are calculated using the universal formula for the average mobilities of carriers in nonhomogeneous doped layers along with Irvin's average conductivity curves. The results are shown graphically.     

Radiative recombination of hot carriers in narrow-gap semiconductors

The mechanism of the radiative recombination of hot carriers in narrow-gap semiconductors is analyzed using the example of indium antimonide. It is shown that the CHCC Auger recombination process may lead to pronounced carrier heating at high excitation levels. The distribution functions and concentrations of hot carriers are determined. The radiative recombination rate of hot carriers and the radiation gain coefficient are calculated in terms of the Kane model. It is demonstrated that the radiative recombination of hot carriers will make a substantial contribution to the total radiative recombination rate at high carrier concentrations.     

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     

The effect of transients on hot carriers

The influence of time-dependent voltages on hot-carrier generation in MOSFETS is studied by transient device simulation. For transient times down to the nanosecond range, no transient effects on hot-carrier formation and injection are found. This result is confirmed experimentally by substrate current measurements under various dynamic voltage conditions down to rise/fall times of 3 ns. This result has important consequences for the interpretation of dynamic stress data, since it means that device-related dynamic effects can be neglected in comparison with interface-related effects in transient ranges relevant to practical applications     

Rashba effect in inversion and accumulation InAs layers

Self-consistent calculations of the Rashba splitting both in inversion and accumulation InAs layers were carried out using a method based on reducing 6×6 and 8×8 Kane matrix equations to a Schrödinger-type equation. Disregarding the Γ₇-band contribution yielded a splitting magnitude overestimated by 50%. The essentially nonlinear dependence of splitting on the two-dimensional (2D) wavevector k restricts the applicability of the Rashba parameter α (coefficient at the k-linear term in the spectrum), including its value at the Fermi level, because of a strong dependence of the latter on the approximations applied to the two-dimensional spectrum. The relative differences Δn/n of the spin-split subband populations, calculated for the inversion layer, were found to be 2–3 times lower than those measured by Matsuyama et al. (see text). The experimental study of accumulation InAs layers showed that the corresponding value Δn/n does not exceed the calculated one, ～0.02. The approach employed to describe the 2D spectrum (including spin-orbit splitting) was also shown to be adequate when applied to the case of quasi-classical quantization in a classically self-consistent surface potential.