Electron-hole Liquid Research Articles

Electron-hole interaction in TmSe1−xTex under pressure

Semiconducting TmSe1−xTex (x=0.55, 0.68) reveals at low temperatures an anomalous peak structure in the resistivity pressure relation followed by a first-order transition into a metallic state. It is believed that the electron-hole interaction plays an important role and speculated that these data show the transition from a normal semiconductor to an excitonic insulator followed by a transition into an electron-hole liquid. Neutron scattering indicates ferromagnetism in pressure-driven metallic TmSe0.45Te0.55 below ∼5 K.

Enhanced recombination through deep impurities within electron-hole liquid in Germanium

Effect of deep double acceptors, Be and Zn, on electron-hole recombination in electron-hole liquid in Ge is studied by means of time-resolved photoluminescence measurements. Non-radiative recombination is strongly enhanced by the double acceptors. Recombination rate per impurity is 7.2 × 10 10 cm 3 s -1 for Be, or 2.6 × 10 -10 cm 3 s -1 for Zn, more than ten times as large as that for shallow acceptor In, 2.2 10 -11 cm 3 s -1.

Elektronno-dyrochnaya zhidkost' i dvumernyi elektronnyi gaz v sloistykh poluprovodnikakh gruppy A<sup>3</sup>V<sup>6</sup>

Электронно-дырочная жидкость Рё двумерный электронный газ РІ слоистых полупроводниках РіСЂСѓРїРїС‹ Рђ³Р’⁶, Беленький Р“.Р›.

Impurity Effects on Strain-Confined Electron-Hole Liquid in Germanium I. Photoluminescence Studies on Recombination Dynamics

This paper deals with impurity effects on recombination dynamics within strain confined electron-hole liquid (SCEHL) in Ge, based on time-resolved measurements of photoluminescence intensity. Double acceptors, Be and Zn, are taken as well as single acceptor In. The double acceptors strongly accelerate non-radiative recombination with SCEHL. At 1.8 K, recombination rate per impurity is 7.2×10 -10 cm 3 s -1 for Be, and 2.6×10 -10 cm 3 s -1 for Zn. These are more than ten times as large as that for In, 2.2×10 -11 cm 3 s -1 . Especially, recombination through Be impurity is due to multiphonon-emission process. The Mott criterion is introduced as a qualitative measure for the difference between the double and the single acceptors. Free-exciton capture cross section by Be or In impurity is also derived.

Impurity Effects on Strain-Confined Electron-Hole Liquid in Germanium II. Millimeter-Wave Studies on Transport Phenomena

From millimeter-wave dimensional resonance experiments, double acceptors, Be and Zn, are found to remarkably increase carrier scattering within strain-confined electron-hole liquid in Ge. Scattering rate of Be impurity is 4.2×10 -4 cm 3 s -1 both for electrons and for holes, while that of Zn impurity is 1.0×10 -4 cm 3 s -1 for electrons and 2.3×10 -4 cm 3 s -1 for holes at 1.6 K. These values are larger than the rate for the single acceptor, In, 4.9×10 -4 cm 3 s -1 . Such a result is interpreted by the Mott criterion in accordance with recombination result obtained by photoluminescence measurements. Temperature dependence of Be-induced scattering rate yields log T behavior. One possible explanation would be a kind of Kondo effect due to the atomic motion of Be impurity.

Variational theory of multicomponent quantum fluids: An application to positron-electron plasmas at T=0.

Variational many-body theory is employed to study ground-state properties of hypothetical positron-electron plasmas. We make use of the multicomponent Fermi hypernetted-chain method to calculate the energy and pair-correlation functions of this system. Optimization of the trial wave function is performed through solving a set of approximate Euler-Lagrange equations for the pair distribution functions. Electron densities are chosen to be in the metallic range, and several concentrations of positrons are considered. At fifty-fifty concentration this system represents an idealized model of the electron-hole liquid and at the limit of zero concentration we have a single positron impurity in an electron gas. Results of this work support earlier theoretical predictions for the model electron-hole liquid and are in good agreement with available experimental evidence for both the electron-hole liquid and the single positron impurity.

On the Bleaching of the A‐Bound Exciton Absorption in GaP: N. An Example for an Electron–Hole Liquid Induced Optical Nonlinearity

AbstractThe intensity dependence of the A‐line absorption in GaP:N is investigated at various nitrogen concentrations and at different excitation conditions, i.e. for resonant and band‐to‐band excitation. For the intensity levels, which are necessary to saturate the absorption, simultaneous luminescence measurements have clearly shown the formation of an electron‐hole liquid in the excited region. An explanation is given of the experimental findings which takes into account the presence of an electron–hole liquid in the sample.

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.

Suppression of Electron-Hole Droplet Transport by Deep Impurities in Germanium

Transport of an electron-hole droplet and the creation of a strain-confined electron-hole liquid in strained Ge doped with a deep impurity Zn were investigated by means of spatial resolution measurements of the recombination luminescence from normal e-h drops as well as a strain-confined large e-h drops under cw-Ar+-laser excitation. A simple drift model is proposed. The drift mobility of an e-h pair composing the droplet decreases from (8.7±0.3)×105 cm2/Vs in pure Ge to (4.5±0.2)×105 cm2/Vs in Zn-doped Ge at 1.8 K. Spatial distribution profiles of free and bound excitons coexisting with e-h drops at 4.2 K are also presented.

Effective interactions for self-energy. II. Application to electron and electron-hole liquids.

Effective masses in an electron gas and an electron-hole liquid are calculated for different values of r/sub s/ and of the ratio M/sub h//M/sub e/ (in the case of the electron-hole liquid) using the self-energy expressions derived in the preceding paper (Ng and Singwi, Phys. Rev. B 34, 7738 (1986)). In the case of an electron gas, it is found that spin-fluctuation effects lead to an appreciable amount of mass enhancement for metallic r/sub s/ values, whereas in the case of an electron-hole liquid, both spin and density fluctuations are important in determining the quasiparticle properties.

Second condensed phase of electron-hole plasma in Si.

Evidence for a condensed phase of plasma in Si above the electron-hole-liquid (EHL) critical temperature (\ensuremath{\cong} 24 K) is presented. The condensed plasma has a density of about one-tenth that of the low-temperature EHL phase and is observed both above and below the EHL critical point. This new low-density liquid appears in the region expected for the metal-insulator transition. A new phase diagram of excitonic matter in Si is presented which is radically different from previous work.

Ultrasonic attenuation in electron-hole liquids.

A theory of the attenuation of longitudinal sound in electron-hole liquids in semiconductors, based on coupled electron and hole kinetic equations, is developed. The theory takes into account the existence of several bands of Fermi liquids, with differing charge and interaction with the lattice, the fact that the Fermi wave numbers are so small that the wave number of the sound can exceed them, and the effects of intraband collisions, which can be rapid enough to produce a significant reduction in the attenuation, even in the high-frequency regime. The theory is applied to sound propagating in the direction in a Ge electron-hole liquid, and the direction in a Si liquid. The former case, compared with the recent experiments by Dietsche, Kirch, and Wolfe (Phys. Rev. B 26, 780 (1982)), suggests that intraband collisions play an important role in the sound-attenuation process.

The electron-hole liquid in semiconductors

Abstract In highly excited semiconductors at low enough temperatures nonequilibrium electrons, holes and excitons condense into droplets of a metallic degenerate Fermi liquid, the so called electron-hole liquid. General properties of this new quantum liquid are reviewed including possible types of its phase diagram; the strong dependence of the phase diagram on the band and crystalline structure of the semiconductor, magnetic field etc.; the kinetics of electron-hole drop nucleation, growth and decay. Electron-hole drops can easily be accelerated by some external forces up to velocities close to that of sound. Intense movement of drops also occurs because of the so called phonon wind-drag by intense flows of nonequilibrium phonons, arising in recombination processes inside the drops themselves or in the therrnalization of excited carriers.

Spatial expansion of electron-hole plasma in Si.

In this paper we report measurements of the spatial and spectral evolution of the photoluminescence resulting from nanosecond pulsed-laser excitation of silicon at low temperatures. An imaging technique employing single-photon counting provides direct measurements of the expansion rates of the electron-hole plasma with 5-ns temporal resolution. We find that for 0.5-\ensuremath{\mu}J excitation energy the plasma expands from the excitation point at subsonic velocities\char22{}contrary to recent claims based on spectroscopic analysis. An alternative analysis of the recombination spectra indicates that local heating can account for the anomalously broad spectra at early times. For 50-\ensuremath{\mu}J excitation, time-resolved images show that the electron-hole plasma expands as a shell into the crystal, indicating that it is driven by an intense phonon wind. The expansion velocities are found to decrease smoothly as the temperature is increased through the critical temperatures (${T}_{c}$\ensuremath{\approxeq}23 K) of the electron-hole liquid (EHL). A theoretical calculation of the phonon-wind-driven expansion velocity yields a temperature dependence which is in reasonable agreement with the data. At low temperatures (l10 K) and near-annealing excitation levels, the EHL expansion velocity is observed to saturate at v=5.1\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/s. We attribute this nonlinear damping to a Cherenkov-like emission of TA phonons from the EHL. Finally, we present measurements of the free-exciton diffusion coefficient for temperatures between 15 and 40 K.

Electron-hole liquid in layered InSe: Comparison of two- and three-dimensional excitonic states.

We have studied the photoluminescence (PL) spectra of the layered semiconductor indium selenide in a wide interval of optical excitation density using stationary and pulse pumping in the temperature range 5--100 K. Analysis of the results at the stationary excitation (SE) density ${I}_{\mathrm{ph}\mathrm{\ensuremath{\le}}{10}^{17}}$ photons/ ${\mathrm{cm}}^{2}$ sec allowed us to determine the binding energy of free and bound excitons in InSe. At 5 K we observed a rebuilding of the spontaneous emission spectrum at the SE density ${I}_{\mathrm{ph}\mathrm{\ensuremath{\approxeq}}{10}^{19}}$ photons/${\mathrm{cm}}^{2}$ sec. A new emission line (K) with a maximum at h\ensuremath{\nu}=1.32 eV appeared and dominated the spectrum. The K line which arose in a threshold ondensation of a gas of direct excitons to an EHL is not at all energetically favorable for 3D excitons. In practice the same is true also for 2D excitons where the difference between the binding energies of the EHL and the excitonic gas is 1.9 meV at T=0 K. It was established that an EHL can be formed only from indirect excitons in both cases. We have determined values for the binding energy of indirect excitons and the EHL as well as the equilibrium density of e-h pairs in the liquid phase at T=0 K. These values are ${E}_{\mathrm{ex}=24}$ meV, ${E}_{L}$=33 meV, and ${n}_{L}$=4.7\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ for 3D excitons and ${E}_{\mathrm{ex}=84}$ meV, ${E}_{L}$=123 meV, and ${n}_{L}$=2.1\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ for 2D excitons. Furthermore, we have calculated the shape of the emission line from the EHL in the 3D and 2D indirect excitonic transition cases. Comparing experimental results and computed parameters for layered InSe, we conclude that the K line is due to recombination of e-h pairs in an EHL which is formed by the condensation of 3D indirect excitons.

Electron-hole liquid in InAs quantum wells under uniaxial stress.

Electron-hole liquid in InAs quantum wells under uniaxial stress.

Binding energy of the electron-hole liquid in quantum wells.

The binding energy and equilibrium density of the quasi-two-dimensional (2D) electron-hole metallic liquid at zero temperature is calculated for GaAs(001) and Ge(001) quantum wells as a function of well width, mass ratio, and electron-band anisotropy. The band-gap renormalization of the electron-hole plasma is calculated for several well widths as a function of density. The calculations are based on an extension to the quasi-2D case (finite well thickness) of the random-phase approximation theory (3D) of Brinkman and Rice, and on a particular model potential used previously for calculating the biexciton binding energy. It is found that the liquid is stable relative to biexcitons for all Ge quantum wells and for GaAs wells of thickness g220 A\r{}. The results in the 2D limit (zero thickness) are in qualitative but not quantitative agreement with those of Kuramoto and Kamimura.

Electron-hole plasma and electron-hole liquid in layered indium selenide

Photoluminescence spectra of layered indium selenide have been stadied in wide temperature range 4.2 + 100 K and a wide interval of optical excitation density (Nex). It is demonstrated that the longwave edge of the K-line undergoes a violet shift with increasing temperature, which confirms the conclusion of /1/ that the K-line (hvmax=1.32 eV) is due to radiative recombination of the e-h pairs in electron-hole liquid (EHL). At pulse excitation (Nex ∼ 1022 phot/sm2.sec) a broad band is observed at the place of excitonic emission lines. The form of this band is described satisfactorily by recombination of the electron-hole plasma. The e-h plasma temperature on the excitation level is estimated. The character of electric field influence upon radiative recombination spectra allows to discuss the mechanism of EHL origin in InSe.

Possibility of superconductivity in the electron-hole liquid

Using the self-consistent STLS approximation of Singwi et al. we have studied the electron correlations in quasi-two-dimensional gas, surrounded by semi-infinite insulating media, including the effect of image charges (EICH) for different layer thickness and electron densities. By numerical self-consistent calculations of the plasmon dispersion, pair correlation function, structure factor, local-field corrections and correlation energy we have shown that for a certain region of electron density and layer thickness it is necessary to include both the correlation effects and the EICH in calculating physical properties of quasi-two-dimensional systems with significant differences between dielectric constants of neighboring media.

Properties of electron-hole liquid in highly stressed silicon

Two independent studies of the electron-hole liquid in stressed Si have provided different values for the ground-state density and the critical temperature of this important Fermi fluid. One set of experiments (by Gourley and Wolfe) was performed using the strain-well configuration while the other (by Forchel et al.) employed uniform strain. These differences raise questions of whether there was some basic difference between the two experimental systems or whether the discrepancies lay in the different methods used for data analysis. In the present joint paper these differences are discussed, several aspects of the data are reanalyzed, some new results are presented, and to a large degree the previous differences are removed. In order to test for possible differences between the line-shape analyses, we use the detailed fitting procedure of Forchel et al. on the strain-well data of Gourley and Wolfe and thereby find a ground-state density of (3.7 +- 0.2) x 10/sup 17/ cm/sup -3/ in the high-stress limit where the effective masses no longer have a stress dependence.