Electron-hole Drops Research Articles

EHD-photoluminescence kinetics in pure Ge at 0.5–1.3 K

Time resolved luminescence experiments show a decrease of the electron-hole drop (EHD) lifetime in pure Ge at very low temperatures (1.3-0.5 K) and extremely weak pulse excitations. Our results indicate that the EHD lifetime decrease is due to increasing ratio of the “hot” Auger-emitted carrier relaxation length to the drop radius.

Temperature dependence of the radius of electron-hole drops in Ge : B. Grossman, K. L. Shaklee and M. Voos. Solid St. Commun.23, 271 (1977)

Temperature dependence of the radius of electron-hole drops in Ge : B. Grossman, K. L. Shaklee and M. Voos. Solid St. Commun.23, 271 (1977)

Theory of the electron-hole droplet magnetoresonance in germanium

A theoretical study is made of the longitudinal magnetoresistance of photoexcited carriers in ultra-pure germanium at 2K in the presence of electron-hole droplet and acoustic deformation scattering for a magnetic field range B=0.19-0.5 T in the orientation j, B parallel to a (100) axis. Numerical calculations based on a relaxation matrix approach to the quantum transport theory reveal an oscillatory component to the magnetoresistance, periodic in B1/2, with fundamental period ( pi /2a)(h(cross)mc/2emz)1/2 where mc and mz are the cyclotron and kinetic masses and a is the radius of an electron-hole drop. The Fourier spectra show a sequence of peaks, each arising from a size resonance between the drop radius and the de Broglie wavelength for maximum momentum transfer in the elastic scattering processes.

Interaction of Electron-Hole Drops with Ballistic Phonons in Heat Pulses: The Phonon Wind

We have performed heat-pulse experiments which graphically demonstrate the strong effect of the phonon wind in propelling electron-hole drops. Investigation of the dynamics of droplet motion sheds light on the mechanisms of propulsion and damping.

New magnetic phase transition between electron-hole drops and free-excitons in pure Ge

We have discovered a new magnetic phase transition between free-excitons and electron-hole drops in high purity Ge near the critical point of the liquid-gas phase diagram. The critical magnetic field is found to be H c ≈ 0.4 T. For H⩾ H c the electron-hole drops are stable to higher temperatures by about 1 K with respect to zero field.

Sign reversals of charge on electron-hole drop

The first self-consisted calculation of surface properties of electron-hole drop (EHD) in Ge is reported. It is predicted that in Ge under <111> uniaxial stress the sign of charge on EHD will undergo two sign reversals; at zero stress the charge on EHD is negative, becomes positive at intermediate stress (⋍ 3 kg mm -2), and then reverses to negative at very large stress. Values of surface energy and dipole layer are given.

Nucleation of electron-hole-drops in Si

Time resolved luminescence spectroscopy in Si, for pump intensities very close to threshold for electron-hole-drops (EHD) formation, shows that optically excited carriers first form excitons which then begin to form EHD after a delay. The origin of this delay has been determined. The measured time of formation of EHD varies by approximately four orders of magnitude for a 30% change in pump intensity, providing a direct confirmation of the predictions of the nucleation theory.

Auger coefficients for highly doped and highly excited silicon

The recombination kinetics in highly doped p- and n-type silicon has been investigated at 77, 300, and 400 K through the radiative band-to-band recombination. The minority-carrier lifetime depends quadratically on the doping concentration as expected for Auger recombination. The Auger coefficients at 300 K for p- and n-type silicon are found to be Cp=9.9×10−32 cm6 s−1 and Cn=2.8×10−31 cm6 s−1. They are nearly independent of temperature in the range investigated. The Auger coefficient in highly excited pure silicon at 4.2 K (electron-hole drops) is essentially the same as in highly doped silicon.

Luminescence from Electron-Hole Drops in Heavily Doped n-Type Germanium

Luminescence spectra in As-doped Ge under intense optical excitation have been observed for varying donor concentration 2.0×10 14 to 4.9×10 18 cm -3 and for varying average density of electron-hole pairs (e-h pairs) in the crystal. From the variation of the luminescence lineshape with the average density of e-h pairs and the theoretical analysis of lineshapes, it is found that even in heavily doped Ge the electron-hole drops (EHD) is stably formed in an atmosphere of metallic electrons and ionized donor impurities. Time resolved spectra at extremly high excitation levels confirm the EHD model of non-equilibrium plasma in heavily doped Ge.

Temperature dependence of the radius of electron-hole drops in Ge

The temperature dependence of the radius of electron-hole drops in Ge is determined from measurements of the number of particles in the drops using the p-n junction technique. The drop radius is found to increase from 5.5μ at 1.7 K to 10μ at 3.2 K for an excitation intensity of 160 mWatt/mm 2. As a function of excitation level at 1.8 K the drop radius is found to increase from 2.9μ at 8 mWatt/mm 2 to 6.5μ at 300 mWatt/mm 2. Our data are compared to results available in this field.

Far-infrared study of excitons, electron-hole drops, and impurity systems in germanium

Decay kinetics of exciton and electron-hole drop systems in a highly photoexcited germanium crystal are investigated by observing time-resolved far-infrared laser magnetoabsorption. Magnetospectroscopy of indium-doped material is also studied over 48-220 μm.

Damping of the motion of electron-hole drops in magnetic fields

We report the observation of an unexpectedly large damping caused by small transverse magnetic fields on the motion of electron-hole drops (EHD) in germanium. Possible causes for the damping are discussed, and we show that the observations are consistent with a mechanism closely related to magnetohydrodynamic damping. Such effects are anomalously large in the EHD system due to its unusually large ratio of electrical conductivity to mass density.

On the low energy tail of the electron-hole drop recombination spectrum

The luminescence line shape of electron-hole drops in germanium is calculated assuming that the final state of the radiative transition is lifetime broadened due to Auger processes in the degenerate bands. This level broadening can account for the existence of the experimentally observed low energy tail in the recombination spectrum. The theoretical line shape is in good agreement with experimental results.

Properties of a giant electron-hole drop in Germanium

We have observed a giant electron-hole drop in an inhomogeneously stressed germanium crystal. Our measurements show that it is a single giant drop of constant liquid density rather than a cloud of smaller droplets. It has a density of 2 x 10 17 electron-hole pairs/cm 3 with a lifetime of only 30 μsec. These results are discussed in the context of earlier reports giving lower densities and longer lifetimes.

Laser Doppler Velocimetry of Electron-Hole Drops in Germanium

We report the first direct measurement of velocity distributions of electron-hole drops, and discuss them in relation to existing theoretical models. The data, obtained by frequency analysis of scattered light, show acceleration near the surface, while at larger depths, the drops appear to experience viscous deceleration with a relaxation time of ${10}^{\ensuremath{-}4}$ sec. We find difficulties in reconciling the data with the present ideas of forces resulting from excitons, phonons, or mutual repulsion.

Net negative charge of electron-hole drops in germanium

The giant fluctuating photocurrent has been observed in highly excited germanium samples with ohmic contacts at 1.6 K. From the observation of this fluctuating photocurrent spike with varying static electric field, it is found that the electron-hole drop is negatively charge as a whole.

Influence of radiation pressure on the electron-hole drop in germanium

Influence of radiation pressure on the electron-hole drop in germanium

Time delay in formation of a γ-phase electron-hole drop in germanium

An explanation is given for the long time delay in the formation of gamma phase EHD in germanium. The Cerenkov radiation of phonons by moving alpha drops at velocity mach 0.2–0.3 is calculated to be the controlling process in the time delay.

Superlattices and electron-hole drops

Report on 13th Annual Conference on the Physics of Semiconductors, 30 August 1976 in Rome, Italy.

Electron—hole liquid in CdS crystals as revealed by non-equilibrium transmission spectroscopy

Transmission measurements in the excitonic region on thin platelets under high N 2 laser excitation showed the disappearance of exciton absorption into a strong absorption continuum. The low energy edge of the latter — about 12 meV below the free exciton A n=1 — coincides with the high energy edge of the gain spectrum of stimulated emission under similar excitations. These results favour the assumption of electron—hole drop formation with a ground state of the e- h-pair about 12 meV below A n=1 .