Electron-hole Plasma In Silicon Research Articles

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.

Recombination of an electron-hole plasma in silicon under the action of femtosecond laser pulses

Experimental data are obtained on the dynamics of conduction-electron relaxation at the stage preceding the melting of a silicon surface layer. The energy of a quantum of probe radiation is smaller than the band gap, making it possible to obtain information about the electron-phonon relaxation processes for an electron concentration of ∼ 1021 cm−3 in the conduction band.

The Self-Compression of Injected Electron-Hole Plasma in Silicon

A recombination radiation line of electron–hole plasma, observed in electroluminescence spectra of tunneling silicon MOS diodes, has been investigated at the temperature T ≥ 300 K. The internal quantum efficiency of the luminescence, equal to (1–3) × 10—3, appears to be unexpectedly high. The spectral position of the luminescence line indicates that a weak overheating of the diode by the diode current results in an anomalously strong reduction of the semiconductor energy gap inside the electron–hole plasma. A unique threshold optical hysteresis is observed in the luminescence intensity with changing diode current. These results are explained by condensation of the injected electron–hole plasma into a dense state. A reduction of the semiconductor energy gap due to generation of phonons by the plasma is discussed as a reason of the plasma condensation. The plasma condensation is identified as the plasma self-compression.

Investigation of the optical, temperature dependent free-carrier absorption of a bipolar electron-hole plasma in silicon

The IR absorption coefficient α(n) for λ=1.32 μm of an electron-hole plasma in silicon at high injection conditions has been measured in dependence of temperature. It was found that the free-carrier absorption (FCA) coefficient α(n) for λ=1.32 μm exhibits a slightly nonlinear dependence on the injected carrier concentration n. The final data were extracted from results obtained from FCA measurements combined with results from open-circuit voltage-decay (OCVD) experiments. For calibration of α specially designed p–i–n diode structures were used at current densities 1≤ j[A/cm 2]≤100.

Optical free-carrier absorption of an electron-hole plasma in silicon.

We present the expression for the free-carrier absorption in a multicomponent plasma, including the contributions from particle scattering, phonon absorption or emission, and impurity scattering. Numerical results are given for the absorption of an electron-hole plasma in silicon. It is found that the contribution from particle scattering dominates for high plasma densities and/or low photon energies.

Comment on "Instability of the electron-hole plasma in silicon"

Comment on "Instability of the electron-hole plasma in silicon"

Surface phase transitions of silicon in the presence of a dense electron-hole plasma

A thermodynamic equation is given, that relates the surface phase transitions with phonon-defect- electron interactions. It permits the calculation of the variation of the phase transition temperatures, T c, with the density of an electron-hole plasma in silicon. Under conditions met in short-pulse laser irradiation, it is shown that T c might differ from thermal values. Also, temperature calculations derived from LEED experiments might be in error, due to electron-phonon couplings.

Lifetime of an electron-hole plasma of silicon in the picosecond range.

A new recombination channel for the electron-hole plasma in silicon, at carrier densities of ${n}_{e}\ensuremath{\gtrsim}{10}^{21}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, is calculated. It is shown to be important in explaining the optical response of the electron-hole plasma at different probing wavelengths generated by picosecond pulses at very large fluences sufficient to melt the sample.

Time-Resolved Spectroscopy of Plasma Resonances In Highly Excited Silicon And Germanium

ABSTRACTThe dynamics of the electron-hole plasma in silicon and germanium samples irradiated by 20 ps, 532 nm laser pulses has been investigated in the near infrared by time-resolved picosecond optical spectroscopy. The experimental reflectivities and transmissions are compared with the redictions of the thermal model for degenerate carrier distributions through the Drue iformalism. Above a certain fluence, a significant deviation between measured and calculated values indicates a strong increase of the recombination rate as soon as the plasma resonances become comparable with the band gaps. These new plasmon-aided recombination channels are particularly pronounced in germanium.

Optical heating of electron-hole plasma in silicon by picosecond pulses

Using a novel three-pulse technique, essential information about the density, optical effective mass, and kinetics of laser-generated plasmas in silicon has been obtained.

Formation of high density electron-hole plasma in silicon metal-oxide-semiconductor transistors below 25 °K

Freezeout of substrate doping impurities, at T<25 °K for conventional shallow level impurities in silicon, creates an insulating substrate in silicon metal-oxide-semiconductor (MOS) transistors. With the flow of majority carriers (holes for p-type substrates) through the substrate impeded, the accumulated majority carrier density in the MOS transistor surface channel must be provided from the sides of the channel. When switched from strong surface accumulation toward surface inversion, a rapidly responding minority carrier density, injected by the source and drain regions, might act to compensate a more slowly responding majority carrier density in the transistor channel, giving rise to anomalously high minority carrier densities. This picture was previously invoked by the author to explain a low level discrete conductance effect seen in a few devices. The other devices exhibit instead a pronounced current spike, which is described here and further supports the initial high charge densities.

Instability of the Electron-Hole Plasma in Silicon

It is shown that the electron-phonon interaction in covalent semiconductors drives an instability in the electron-hole plasma at high temperature. The instability might be the reason for melting of tetrahedrally bound semiconductors. If this is true, the intrinsic carrier concentration of silicon at the melting temperature would be of the order of ${10}^{21}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ instead of the commonly accepted value of 2\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$.