Nonequilibrium Electron-hole Plasma Research Articles

Self-sustaining conducting state and bipolar ionizing Gunn domains in pulse avalanche GaAs diodes

Domain instability in nonequilibrium electron-hole plasma leads to the formation of narrow moving regions of the ionizing electric field—collapsing Gunn domains. In pulse power electronics devices based on gallium arsenide, impact ionization in collapsing domains acts as an efficient mechanism for the generation of nonequilibrium carriers at low voltages and weak average electric fields.

Multi-zone resonance spectrometry of inelastic electron scattering of light and the manifestation of strong spin-orbit interaction in nanostructures with quantum dots

Highly sensitive methods of inelastic light scattering spectrometry have been developed to detect individual photons in the visible and near-infrared spectral ranges (0.4-1.35) μm. Precision optical measurements of vibrational and electronic states of nanostructures with quantum objects are performed, using the example of quantum-dimensional nanoheterostructures (311)In si-GaAs/InAs with InAs quantum dots. A distinctive attractive feature of such structures with a degenerate valence band of symmetry 8 is the presence of a strong spin-orbit interaction. In this case, the intrinsic moment of the holes can effectively interact with the electric field of the incident light wave. It was found that such interaction causes intense luminescence and inelastic scattering of the light wave in the IR region of the 0.9-1.35 μm spectrum. Effective generation of nonequilibrium electron-hole (e-h) plasma with concentrations n=p=1.0·1017 cm-3 and T_e=T_h=25 K,was revealed under resonant excitation conditions, while the lattice temperature T_L=5.1 K. New mechanisms have been discovered for the formation of an abnormally intense integration spectrum of multiplex inelastic light scattering of a rather complex shape formed by various separable resonant contributions of the processes of quasi-elastic scattering by charge carriers, light scattering by acoustic plasmons of electron-hole plasma, as well as inelastic intra- and inter-band light scattering by heavy holes. It has been established that the anomalous intensity gain of such multi-zone selective resonant light scattering is more than 105 times higher than the intensity of Thomson light scattering on individual charge carriers. There is agreement between the estimated calculated and experimental spectra, and for the most part for the difficult-to-interpret significant width of the observed light scattering line. It is shown that new mechanisms of various contributions to the formation of scattered photon radiation are important diagnostic elements that are clearly manifested in the spectra of the resulting enhanced inelastic light scattering. Keywords: nanostructures, quantum objects, resonant scattering of light by charge carriers, exchange interaction, plasma diagnostics.

Heat capacity of nonequilibrium electron-hole plasma in graphene layers and graphene bilayers

We analyze the statistical characteristics of the quasi-nonequilibrium two-dimensional electron-hole plasma in graphene layers (GLs) and graphene bilayers (GBLs) and evaluate their heat capacity.The GL heat capacity of the weakly pumped intrinsic or weakly doped GLs normalized by the Boltzmann constant is equal to $c_{GL} \simeq 6.58$. With varying carrier temperature the intrinsic GBL carrier heat capacity $c_{GBL}$ changes from $c_{GBL} \simeq 2.37$ at $T \lesssim 300$~K to $c_{GBL} \simeq 6.58$ at elevated temperatures. These values are markedly differentfrom the heat capacity of classical two-dimensional carriers with $c = 1$. The obtained results can be useful for the optimization of different GL- and GBL-based high-speed devices.

Double Avalanche Injection in Diode Avalanche Sharpeners

Picosecond-range avalanche sharpening diodes commutating fast-rising high-voltage pulses of submicrosecond duration are simulated numerically. It is demonstrated that the maximum duration of the commutated pulse are limited by physical phenomena related to the transition of the diode to the double-avalanche-injection mode instead of the drift extraction of nonequilibrium electron–hole plasma. Double avalanche injection is in principle capable of supporting the diode structure in the conducting state after switching. However, the negative differential conductivity, which is attributed to the double injection mode, causes the transverse instability of uniform current distribution and isothermal current filamentation.

Semiconductor Plasma Antennas Formed by Laser Radiation

Efficiency of the transmission of high-frequency signals by semiconductor plasma antennas based on Ge and Si single crystals with surface nonequilibrium electron-hole plasma generated by laser diode radiation has been experimentally studied. Dependences of the amplitude of a radiated 6- to 7.5-GHz microwave signal on the laser power and size of the laser-irradiated region on the semiconductor transmitting dipole antenna are determined. It is shown that a more than tenfold increase can be achieved in the efficiency of useful signal transmission by the plasma antenna formed in Ge crystals.

Picosecond-Range Avalanche Switching of Bulk Semiconductors Triggered by Steep High-Voltage Pulses

Experimental observation and numerical simulations of sub-nanosecond avalanche switching of Si and ZnSe bulk semiconductor structures initiated by high-voltage pulses with steep (dU / dt > 10 kV/ns) ramp are reported. The measured switching time is ~100ps. The switching is sustainable and repetitive and has negligible jitter. Comparison of the experimental and numerical results suggests that after switching, the whole volume of the structure is uniformly filled with nonequilibrium electron-hole plasma.

Полупроводниковые плазменные антенны, формируемые лазерным излучением

The efficiency of transmission of high-frequency signals by a semiconductor-transmitting antenna made of Ge and Si single crystals on the surface of which a nonequilibrium electron-hole plasma is formed by laser diode radiation is experimentally investigated. The dependences of the amplitude of the emitted microwave signal in the range of 6 - 7.5 GHz on the laser power and the size of the irradiated area on the semiconductor transmitting vibratory antenna are obtained. It is shown that the efficiency of the useful signal transmission when forming a plasma antenna in Ge crystals can be increased by more than an order of magnitude.

Magnetization and diamagnetism of a longitudinal autosoliton in p-InSb in an external longitudinal magnetic field

It has been experimentally shown that a longitudinal thermal-diffusion autosoliton, which is generated in a nonequilibrium electron–hole plasma in p-InSb, in an external longitudinal magnetic field acquires diamagnetic properties. The results of the calculation and numerical estimates of the diamagnetism have been presented.

Investigation of non-equilibrium electron-hole plasma in nanowires by THz spectroscopy

Efficient emission of THz radiation by AlGaAs nanowires via excitation of photocurrent by femtosecond optical pulses in nanowires was observed. Dynamics of photoinduced charge carrier was studied via influence of electron-hole plasma on THz radiation by optical pump THz probe method. It was found that characteristic time of screening of contact field is about 15 ps. Recombination of non-equilibrium occurs in two stages: fast recombination of free electron and holes (with relaxation time about 700 ps), and slow recombination (with relaxation time about 15 ns), which involves a capture of electrons and holes on the defects of crystalline structure of nanowires.

Relativistic Doppler reflection as a probe for the initial relaxation of a non-equilibrium electron-hole plasma in silicon

This paper reviews the status of investigations of the relativistic Doppler reflection of a broadband terahertz pulse at a counter-propagating plasma front of photo-excited charge carriers in undoped silicon. When a THz pulse with 20-THz bandwidth impinges onto a moving plasma front with a carrier density in the range of 1019 per cm3, one observes a spectral up-shift, which is, however, much less pronounced than expected from simulations assuming a Drude plasma characterized by a single carrier relaxation time τ of the order of 15-100 fs. Qualitative agreement between simulations and experiments can be achieved if τ is chosen to be less than 5 fs. In order to explore carrier relaxation in more detail, optical-pump/THz-probe experiments in the conventional co-propagation geometry were performed. If the pump-probe delay is long enough for monitoring of the equilibrium value of the scattering time, τ ranges from 200 fs at low carrier density to 20 fs in the 1019-cm-3 density range. For small (sub-picosecond) pump-probe delay, the data reveal a significantly faster scattering, which slows down during energy relaxation of the charge carriers.

Anomalous dynamics of the residual voltage across a gallium-arsenide diode upon subnanosecond avalanche switching

A qualitative difference between high-voltage gallium-arsenide diodes and similar silicon devices is found experimentally upon ultrafast switching in the delayed avalanche breakdown regime. It is shown that, following switching, a gallium-arsenide diode remains in a highly conductive state throughout the entire duration of the applied voltage pulse and the recovery of the reverse voltage across the p-n junction due to the dispersal of nonequilibrium electron-hole plasma is not observed. In the same interval of time (2 ns in our experiment), a silicon diode passes completely into a blocking state. The residual voltage amplitude for a gallium-arsenide diode is an order of magnitude lower than that for a silicon device. The discovered effect is similar to a known effect of “sticking” of gallium-arsenide diode switches (the lock-on effect), which are triggered by a laser pulse, in a conductive state.

Ultrafast coupling of coherent phonons with a nonequilibrium electron-hole plasma in GaAs

We present a joint experimental theoretical study of the coupling of coherent phonons in bulk GaAs with a nonequilibrium electron-hole plasma following photoexcitation at the ${E}_{1}$ gap by ultrafast laser pulses. In contrast to prior coherent phonon experiments where photoexcitation across the ${E}_{0}$ gap generated electrons in the $\ensuremath{\Gamma}$ valley, for the ${E}_{1}$ gap excitation, the majority of the electrons are generated in the satellite $L$ valleys. This leads to a drastically different situation from the previous studies because the damping of electrons is now faster due to the higher scattering rates in the $L$ valley, and, in addition, the diffusion of carriers has a significant effect on the plasma response due to the shorter optical absorption depth of the pump-probe light. Reflectivity measurements show coherent phonon-plasmon oscillations, whose frequencies lie between the transverse and longitudinal optical phonon frequencies due to the heavy damping and change with time due to the diffusion of the plasma. We analyze the experimental data with a theoretical model that describes the time and density-dependent coupling of the coherent phonon and the electron-hole plasma as the photoexcited carriers diffuse into the sample on a subpicosecond time scale. The calculated phonon-plasmon dynamics qualitatively reproduce the experimentally observed time-dependent frequency.

Specific features of formation and evolution of a longitudinal autosoliton in p-InSb in a longitudinal magnetic field

The effect of a longitudinal magnetic field on the formation and behavior of a longitudinal autosoliton in the excited nonequilibrium electron-hole plasma in p-InSb is studied experimentally. It is shown that, in a longitudinal magnetic field, the threshold characteristics of the formation of an autosoliton are reduced and the autosoliton takes on the diamagnetic properties that persist after removal of the magnetic field. In magnetic fields of 9.6 × 103—4.6 × 104 A m-1, instabilities of the autosoliton current are excited, with a frequency in the range 2–20 kHz. In this case, the amplitude and frequency of these instabilities depend on the magnetic field. At elevated levels of excitation of the autosoliton and in increased magnetic fields, the instability of the longitudinal-autosoliton current exhibits synergetic properties.

Generation of terahertz radiation by a moving bunch of nonequilibrium electron-hole plasma

We report on properties of coherent radiation from nonequilibrium electron-hole $(e\text{\ensuremath{-}}h)$ plasma bunch excited by an ultrashort laser pulse crossing a semiconducting slab subject to transverse bias voltage. Self-consisted calculations of nonequilibrium Boltzmann and Maxwell equations have established the fundamental role of uniformly moving bunch of $e\text{\ensuremath{-}}h$ plasma in coherent generation of terahertz radiation. We have shown that predicted properties crucially depend on the physics of dissipation mechanisms, current configurations, and relative traveling velocities of $e\text{\ensuremath{-}}h$ plasma bunch and terahertz radiation pulse. It has distinguished two major regimes of terahertz emission, single pulse emission, and firing twinned pulses at the moments of creation and extinction of moving bunch of $e\text{\ensuremath{-}}h$ plasma related to the front and rare boundaries of semiconducting slab, respectively. The results of developed theory are applied to enhance the performance of photoconductive terahertz emitters.

Ultrashort excitations of surface polaritons and waveguide modes in semiconductors

Polarization-dependent structures have been formed on the silicon surface under the action of femtosecond laser pulses. Some model concepts are proposed to describe changes in the response of the semiconductor surface caused by the generation of a nonequilibrium electron-hole plasma and explain the excitation of surface polaritons and waveguide modes during a femtosecond laser pulse.

Effect of transverse magnetic field on the behavior of longitudinal autosolitons in p-InSb

The behavior of a longitudinal autosolitons created in excited nonequilibrium electron-hole plasma in compensated p-InSb in crossed magnetic and electric fields is studied experimentally. It is shown that, in magnetic fields ranging from 6.7 × 102 to 3.2 × 104 A/m, a longitudinal autosoliton is in a state of motion with the average velocity 2 × 102−3 × 103 cm/s towards the sample periphery, where the temperature is reduced and the autosoliton is unstable, making the process cyclic and giving rise to oscillations of the current in the external circuit of the sample. In this case, the amplitude and frequency of the oscillations (2144-26855 Hz) depend on the magnetic field. With increasing electric and magnetic fields, the instability of the longitudinal autosoliton current takes on synergetic properties.

Ultrafast electron-phonon decoupling in graphite

We report the ultrafast dynamics of the $47.4\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ coherent phonons of graphite interacting with a photoinduced nonequilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the nonadiabatic electron-phonon interaction by creating a nonequilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast nonquilibrium electron dynamics.

Longitudinal autosoliton motion across p-InSb in a transverse magnetic field

It is experimentally shown that a longitudinal autosoliton excited by an electric field in nonequilibrium electron-hole plasma in p-InSb moves towards the sample periphery under the effect of a transverse magnetic field. This sample region is characterized by a lowered temperature and by the fact that the unstable existence of the autosoliton leads to a cyclic process causing current oscillations in the sample circuit. An average velocity of the autosoliton motion amounts to 2 × 102−3 × 103 cm/s in a magnetic field within the range of 5962.5–22657.5 A/m.

On the hot and cold autosolitons in dissipative semiconductor structures

It is experimentally shown that in bulk InSb and Te single crystals, during the formationand excitation of the dissipative structure in the non-equilibrium electron–hole plasma, inthe case of a presence of longitudinal autosolitons, the carrier concentration decreasesoutside the autosolitons, while it increases in the case of transverse autosolitons.The longitudinal autosolitons, forming in the non-equilibrium electron–hole plasma byJoule heating, are considered to be cold, and the transverse autosolitons to be hot.

How fast do charged particles get dressed?

AbstractOn a femtosecond timescale, we observe how Coulomb screening and collective scattering build up in an extreme nonequilibrium electron–hole plasma photoinjected in GaAs. To this end, we generate a plasma within 10 fs and probe the subsequent polarization response of the system with uncertainty‐limited temporal resolution via ultrabroadband THz spectroscopy. We show that the intrinsic material becomes conductive instantaneously upon carrier injection, whereas collective effects such as Coulomb screening and plasmon scattering exhibit a delayed onset. Thus, the ultrafast formation of dressed quasiparticles is directly monitored for the first time. The timescale for these phenomena is of the order of the inverse plasma frequency. Our findings support recent quantum kinetic simulations.