R. Raguotis

Bio: R. Raguotis is an academic researcher. The author has contributed to research in topics: Monte Carlo method & Electric field. The author has an hindex of 3, co-authored 10 publications receiving 26 citations.

Monte Carlo calculations of the electron impact ionization in n-type InSb crystal

Abstract: Monte Carlo computer simulations of electron impact ionization in InSb crystal are carried out for both instantly switched on dc and high-frequency electric fields. It is established that the rate of generation of electron–hole pairs decreases with the increase of electric field frequency, due to the inertia of electron heating by high-frequency electric field. For fields oscillating at frequencies much higher than the reciprocal momentum relaxation time, the impact ionization threshold field is found to be a linear function of frequency. Good agreement between calculations and available experimental data has been obtained.

Impact ionization and intervalley electron scattering in InSb and InAs induced by a single terahertz pulse

Abstract: Electronic properties of InSb and InAs are sensitive to electric field due to their narrow forbidden energy gaps and big difference in effective masses of electrons in different conduction band valleys Here we report impact ionization processes and redistribution of electrons between the Γ, L and X valleys induced by a single ultrashort terahertz (THz) pulse at 80 K temperature Monte Carlo simulation revealed that electron motion in this case has near ballistic character The threshold electric field of impact ionization increases as the THz pulse gets shorter, and the process of impact ionization essentially raises cooling rate of hot electrons The L valley gets mainly occupied by electrons in InSb while the X valley holds the majority of electrons in InAs at strong electric fields, respectively above 20 kV/cm and 90 kV/cm The calculated results are in good agreement with the available experimental data

Monte Carlo study of impact ionization in n-type InAs induced by intense ultrashort terahertz pulses

Abstract: Electron impact ionization induced in n-type InAs by single-cycle pulses of picosecond and subpicosecond duration has been investigated by Monte Carlo method. It is established that the rate of generation of electron–hole pairs decreases with the decrease of the pulse duration. The impact ionization threshold field is found to depend linearly on frequency for the fields oscillating at frequencies much higher than reciprocal momentum relaxation time. Good agreement between calculations and available experimental data has been obtained.

Monte Carlo Treatment of Non-Equilibrium Processes in n-Type InSb Crystals

Abstract: Numerical calculation by Monte Carlo method of the dynamic behaviour of electron ensemble in n-type InSb crystals after step-like application of electric fleld is presented. The results show essential in∞uence of electron density on the energy relaxation time. The efiect of electron energy cooling below equilibrium temperature in compensated n-InSb is obtained numerically for the flrst time, which is in agreement with experimental results.

Monte Carlo study of impact ionization in InSb induced by intense ultrashort terahertz pulses

Abstract: The electron impact ionization dynamic has been investigated by Monte Carlo method in n-type InSb under the action of single-cycle pulses with 1 ps duration. The threshold electric field of impact ionization has been estimated to be about 8 kV/cm at 80 K. The number of generated carriers increases rapidly with increasing of electric field strength over threshold, and at 100 kV/cm, normalized electron concentration reaches 14. It is found that impact ionization process is dominant energy loss mechanism for hot carriers with energy larger than threshold energy of impact ionization. The results of calculations are compared with available experimental data. The agreement between theoretical calculations and experimental results was obtained.

The Monte Carlo method for semiconductor device simulation

Abstract: There can be little doubt that the Monte Carlo method for semiconductor device simulation has enormous power as a research tool. It represents a detailed physical model of the semiconductor material(s), and provides a high degree of insight into the microscopic transport processes. However, if the authority ascribed to Monte Carlo models of devices at 1/spl mu/m feature size is to be maintained for devices below O.1/spl mu/m, modelling of the fundamental physics must be further improved. And if the Monte Carlo method is to be successful as a semiconductor device design tool, the device model must be made more realistic. Success in the industrial sector depends on this, but also on achieving fast run-times optimisation - where the scope and need for ingenuity is now greatest.

Unraveling the Ultrafast Hot Electron Dynamics in Semiconductor Nanowires.

Abstract: Hot electron relaxation and transport in nanostructures involve a multitude of ultrafast processes whose interplay and relative importance are still not fully understood, but which are relevant for future applications in areas such as photocatalysis and optoelectronics. To unravel these processes, their dynamics in both time and space must be studied with high spatiotemporal resolution in structurally well-defined nanoscale objects. We employ time-resolved photoemission electron microscopy to image the relaxation of photogenerated hot electrons within InAs nanowires on a femtosecond time scale. We observe transport of hot electrons to the nanowire surface within 100 fs caused by surface band bending. We find that electron-hole scattering substantially influences hot electron cooling during the first few picoseconds, while phonon scattering is prominent at longer time scales. The time scale of cooling is found to differ between the well-defined wurtzite and zincblende crystal segments of the nanowires depending on excitation light polarization. The scattering and transport mechanisms identified will play a role in the rational design of nanostructures for hot-electron-based applications.

State-resolved ultrafast dynamics of impact ionization in InSb.

Abstract: Impact ionization (IMP) is a fundamental process in semiconductors, which results in carrier multiplication through the decay of a hot electron into a low-energy state while generating an electron-hole pair. IMP is essentially a state selective process, which is triggered by electron-electron interaction involving four electronic states specified precisely by energy and momentum conservations. However, important state-selective features remain undetermined due to methodological limitations in identifying the energy and momentum of the states involved, at sufficient temporal resolution, to reveal the fundamental dynamics. Here we report state-resolved ultrafast hot electron dynamics of IMP in InSb, a semiconductor with the lowest band-gap energy. The ultrafast decay of state-resolved hot-electron populations and the corresponding population increase at the conduction band minimum are directly captured, and the rate of IMP is unambiguously determined. Our analysis, based on the direct knowledge of state-resolved hot electrons, provides far deeper insight into the physics of ultrafast electron correlation in semiconductors.

Observation of nonequilibrium carrier distribution in Ge, Si, and GaAs by terahertz pump-terahertz probe measurements

Abstract: We compare the observed strong saturation of the free-carrier absorption in $n$-type semiconductors at 300 K in the terahertz (THz) frequency range when single-cycle pulses with intensities up to $150\text{ }\text{MW}/{\text{cm}}^{2}$ are used. In the case of germanium, a small increase in the absorption occurs at intermediate THz pulse energies. The recovery of the free-carrier absorption was monitored by time-resolved THz pump--THz probe measurements. At short probe delay times, the frequency response of germanium cannot be fitted by the Drude model. We attribute these unique phenomena of Ge to dynamical overpopulation of the high mobility $\ensuremath{\Gamma}$ conduction-band valley.

Noise-induced resonance-like phenomena in InP crystals embedded in fluctuating electric fields

Abstract: We explore and discuss the complex electron dynamics inside a low-doped n-type InP bulk embedded in a sub-THz electric field, fluctuating for the superimposition of an external source of Gaussian correlated noise. The results presented in this study derive from numerical simulations obtained by means of a multi-valley Monte Carlo approach to simulate the nonlinear transport of electrons inside the semiconductor crystal. The electronic noise characteristics are statistically investigated by calculating the correlation function of the velocity fluctuations, its spectral density and the integrated spectral density, i.e. the total noise power, for different values of both amplitude and frequency of the driving oscillating electric field and for different correlation times of the field fluctuations. Our results show that the nonlinear response of electrons is strongly affected by the field fluctuations. In particular, crucially depending on the relationship between the correlation times of the external Gaussian noise and the timescales of complex phenomena involved in the electron dynamical behavior: (i) electrons self-organize among different valleys, giving rise to intrinsic noise suppression; (ii) this cooperative behavior causes the appearance of a resonance-like phenomenon in the noise spectra.