Excitons and electron-hole plasma in InSe

The spontaneous emission from either thin or thick samples of layered indirect-gap InSe semiconductor under dye laser excitation has been investigated either above or below the critical Mott density. The observed spectra consist of five bands in the near infrared region; four of them are localized in the energy range between the direct and the indirect gap and one only lies below the indirect energy gap. These bands can be associated with cooperative indirect and direct excitonic transitions and with electronhole plasma recombinations.     

Impact-ionized electron-hole plasma instability in GaAs

The possibility of the excitation of impact-ionized electron-hole plasma oscillatory instability in GaAs with frequency up to 10¹² Hz is shown. The linear and nonlinear stages of the instability are investigated.     

Luminescence from compressed electron-hole plasma in germanium

We have studied the luminescence spectra from compressed electron-hole plasma in pure germanium. The spectra show a satisfactory thermalization of the charge carriers and lead to a reasonable value of the compressibility. These features encourage to further experimental efforts in the studies of the Mott transition in highly excited semiconductors.     

Excitons and electron-hole plasma in quasi-two-dimensional systems

A theoretical study of many-body effects in quasi-two-dimensional electron-hole systems is presented. The renormalized single-particle energies and the exciton binding energy are calculated as functions of the carrier density and temperature. A simple model for the nonlinear excitonic absorption and refraction is proposed.     

Stochastic resonance in a nonequilibrium electron-hole plasma

A photogenerated electron-hole plasma, heated in the process of Auger recombination, is studied. It is shown that in the plasma near the threshold for the appearance of uniform relaxational self-excited oscillations, weak noise transforms into a stochastic sequence of large-amplitude spikes. An additional optical periodic signal with amplitude approximately five times smaller than the noise variance, depending on the form of this signal, transforms these stochastic oscillations into low-amplitude quasiharmonic oscillations or into periodic spike self-excited oscillations of enormous amplitude. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 422–427 (10 October 1999)     

Cooling of high density electron-hole plasma

We generalize for high density electron-hole plasma, the previous theories [12] of temperature cooling of non-equilibrium hot plasma. Especially we take into account the cooling by emission of mixed longitudinal optical phonon and plasmon modes, these quasiparticles described by a non-equilibrium distribution function. We show that a strong slowing of the plasma cooling occurs, at high electron-hole density. We calculate for CdSe the temperature kinetics of plasma created by Yag laser (pulse duration 30 ps).     

Nonequilibrium properties of electron-hole plasma in direct-gap semiconductors

The gain spectra of the electron-hole plasma recombination in CdS are investigated as a function of the excitation conditions and of the lattice temperature. From a lineshape analysis which includes such many-body effects as collision broadening, single-particle energy renormalization and excitonic enhancement, average plasma parameters are obtained. In contrast to the predictions of quasi-equilibrium theory, one finds that the electron-hole plasma does not reach a full thermal quasi-equilibrium in direct-gap materials because of the short lifetimes of the carriers. The nonequilibrium effects are shown to lead to the formation of electron-hole plasma density fluctuations. No well-defined coexistence region exists. The experimental results in the phase transition region can consistently be explained by theoretical treatments of this nonequilibrium phase transition.     

Luminescence of direct-and indirect-gap electron-hole plasma in TlBr

Luminescence of TlBr crystals highly excited by a nanosecond pulsed-dye laser (3.4 eV) at the bath temperature ∼ 8.5 K was studied. Two emission lines labeled A (∼ 2.98 eV) and B (∼ 2.62 eV) were found, which show typical behavior of the electron-hole plasma recombination radiation. The A-line is assigned to the recombination of e-h pairs in the direct gap (X⁺₆−X^-₃) and the B-line to the simultaneous recombination in the indirect gap (X⁺₆−R^-₆). Condensation of carriers into an electron-hole liquid was not observed.     

Autosolitons in systems with global nonlinearity

We consider the simplest mathematical model of localized dissipative structures described by a single diffusive equation with the source containing both local and global nonlinearities, i.e., depending on an integral of the unknown function over the entire volume. On the basis of qualitative analysis, we find out that stable autosolitons exist in the medium considered. This conclusion is confirmed by the results of numerical simulation of a three-dimensional problem. We determine the dependence of the autosoliton power on the parameters of the problem. Metastable multisoliton states are found and their properties are studied. The possibility of stabilization of three-dimensional autosolitons in a system without local losses is considered.     

Current injected electron-hole plasma in GaP pin-device structures

We report first on an electrically generated electron-hole plasma (EHP) in GaP light emitting diodes having a pin-structure. For current densities above j ? 10³Acm^?2 and at T = 77 K a dense EHP is formed within the i-region whose carrier density can easily be changed by the injection level. The corresponding electron-hole pair densities n of the plasma and the resulting gap shrinkage ΔE_g have been determined using a least-squares fit of the EHP luminescence spectra. The lineshape analysis of the spectra yields a $\text{n}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ -dependence of the gap shrinkage in quantitative agreement with findings from optically excited EHP and corresponding theoretical work. From electrical investigations it can be concluded that the EHP causes a strong nonlinear behaviour of the current-voltage characteristics.     

Energy relaxation of an electron-hole plasma in semiconductors

We calculate the energy relaxation of an electron-hole plasma created by a short laser pulse in semiconductors like Si and GaAs in two cases: (i) when the carrier-carrier collision time is much shorter than the carrier-phonon one, so that a carrier temperature T_c exists. We give the variation of T_c with time; (ii) when there is no carrier temperature and the initial energy distribution is a peaked function of width Δ. We give the time evolution of the system when Δ is much larger and much smaller than the phonon energy.     

Instability of photoexcited electron-hole plasma in short semiconductor structures

The instability of the electron-hole plasma produced by continuous photoexcitation in short semiconductor structures is investigated theoretically. The applied electric field is considerably disturbed by photogenerated charge carriers. At a sufficiently intensive photogeneration plasma instability occurs. The frequency of current oscillations due to the instability, as shown by numerical simulation for a GaAs structure, is in the range of 10¹¹–10¹²s^–1.     

Experimental investigation of the electron-hole plasma expansion in CdS

Using a two beam method for gain and reflection spectroscopy, we introduce a new technique allowing for a spatial and temporal resolution of 5 μm and 2 nsec, respectively. With this method we are able to investigate the optical gain, the reflection and the spatial extension of an electron-hole plasma under stationary excitation conditions. The experiments are performed with the II–VI compound semiconductor CdS. Our results are compared with those from other authors who deduced the electron-hole plasma properties mainly from luminescence experiments.     

Self-focusing of electromagnetic waves in a degenerate electron-hole plasma

The free carrier nonlinear dielectric constant of a degenerate electron-hole plasma (e.g., Ge) in the presence of a Gaussian electromagnetic beam has been studied by a kinetic treatment. The redistribution of carriers (electrons and holes) is the source of nonlinearity and is effective in causing the self-focusing of the beam. The rise in carrier temperature due to the wave field is almost unaffected by the degeneracy, whereas the nonlinearity is considerably affected by it. The increase of degeneracy (by increasing the equilibrium carrier concentration at the fixed lattice temperature) increases the nonlinear dielectric constant. Hence self-focusing is enhanced by degeneracy. This work was supported by NSF (USA) and CSIR (India).     

Transient strain driven by a dense electron-hole plasma

We measure transient strain in ultrafast laser-excited Ge by time-resolved x-ray anomalous transmission. The development of the coherent strain pulse is dominated by rapid ambipolar diffusion. This pulse extends considerably longer than the laser penetration depth because the plasma initially propagates faster than the acoustic modes. X-ray diffraction simulations are in agreement with the observed dynamics.     

Electronic fine structure in the electron-hole plasma in SrB6

Electron-hole mixing-induced fine structure in alkaline earth hexaborides leads to lower energy (temperature) scales, and thus a stronger tendency toward an excitonic instability than in their doped counterparts (viz. Ca1-xLaxB6, x approximately 0.005), which are high-Curie-temperature, small-moment ferromagnets. Comparison of Fermi surfaces and spectral distributions with de Haas-van Alphen, optical, transport, and tunneling data indicates that SrB6 remains a fermionic semimetal down to (at least) 5 K, rather than forming an excitonic condensate. For the doped system the Curie temperature is higher than the degeneracy temperature.     

Thermal emission spectrum from a semiconductor electron-hole plasma

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 624–629, October, 1991.     

High density electron-hole plasma in Si induced by femtosecond pulses

High electron and hole (e-h) densities of about 10²² cm^-3 have been produced in silicon, using 620 nm wavelength laser pulses of 100 fs duration. These density values are determined by measuring the dependence of the pulse self-reflectivity on its energy. By comparison with a fully non-linear model of light propagation, we show that dissipation processes inside the plasma are dominated by e-h collisions, with a characteristic time of 3 × 10^-16s. The onset of melting within 100 fs and its nature, considering the high plasma density, are also discussed in view of scattered light measurements.