Semiconductor Plasma Research Articles

In situ spectral ellipsometry for real-time thickness measurement: Etching multilayer stacks

A polarization modulated spectroscopic ellipsometer is used in situ to measure the thicknesses of films in real time during semiconductor plasma etch processing. Utilizing the speed of phase modulation multichannel detection, and digital signal processing techniques, this ellipsometer is capable of acquiring spectral data in less than 75 ms. Efficient algorithms were developed for determining layer thicknesses from the measured spectra of multilayer film stacks in real time with a typical solution time of a few seconds. The measured thicknesses and etch rates are used to anticipate interfaces in multiple layer stacks and control process end points. The ability of the spectral ellipsometer to measure multilayer stacks during etching is demonstrated by the etching of a stack consisting of silicon nitride, polycrystalline silicon, and silicon dioxide. Such stacks are commonly used as masks for field oxidation for electrical isolation in memory device fabrication. An isotropic plasma etch is used to remove this film in a single-wafer process environment.

Exclusion effects revisited: nontraditional use of narrow-gap semiconductors

Investigations of carrier exclusion as a possible way to considerably disturb the electron-hole plasma in narrow-gap semiconductors have enabled one to reveal and to use for practical purposes such nontrivial effects as the negative differential conductivity, the suppression of Auger generation of carriers, the negative luminescence and radiative cooling. The physical nature of these effects and the principles of their use in new semiconductor devices are discussed.

Light and field control of light in polariton-active metal-semiconductor structures: interface polariton optoelectronics

This paper considers photoelectric and field modes of controlling the behaviour of interface polaritons in polariton-active metal-semiconductor structures by changing the semiconductor plasma frequency. The principle can be used to control light reflected from the structure. It is shown that a wide variety of optoelectronic devices can be constructed on this basis: modulators tunable over a wide frequency range (controlled reflectors), tunable filters, space modulators, optical transistors and other data-processing units. The principles of controlling the interface polariton characteristics open up new possibilities for resonance diagnostics, namely the study of kinetics of a high-field domain entering the contact, contact potential difference microscopy, analysis of the degree of uniformity of the potential barrier thickness, etc.

In-plane transport of photoexcited carriers in GaAs quantum wells.

We have measured the picosecond-time-resolved in-plane motion of carriers in a multiple quantum well by a spatially scanned pump-probe technique at bath temperatures between 8.5 and 60 K. The effective ambipolar diffusivity measured from the spatial expansion of a nonequilibrium carrier distribution is found to increase with pump power, i.e., carrier density. We believe that this effect is in part due to the formation of a degenerate semiconductor plasma and to screening of scattering centers. An increase in the diffusivity is observed with the change in the bath temperature from 8.5 to 60 K that is consistent with a simple impurity-limited scattering model. The diffusivity at 0--200 ps is found to increase with the incident photon energy, while the diffusivity measured at 500 ps remains relatively constant with increasing photon energy. The decrease in the expansion rate with time is ascribed to the decreasing kinetic energies of the carriers.

An additional solution of the waveguide problem for a waveguide partially filled with a magnetoactive semiconductor plasma

A new method of solving the waveguide problem for a waveguide partially filled with a magnetoactive semiconductor plasma is proposed. This method is valid for cases when one of the transverse wavenumbers is zero and it is an addition to the well-known ones.Useful effects for the aims of powerful electronics are shown. The paper makes the conclusion that a waveguide with a semiconductor sleeve is significantly more perspective than the waveguide with semiconductor column for effective interaction between waveguide eigenmodes and relativistic electron beam.

Ultrafast dephasing through acoustic plasmon undamping in nonequilibrium electron-hole plasmas.

Strong enhancement of acoustic plasmons in optically excited nonequilibrium electron-hole plasmas in bulk semiconductors is shown to cause ultrashort (\ensuremath{\sim}10 fs) dephasing times and very high carrier-carrier scattering rates.

Kink instability of the semiconductor plasma in silicon parallelepipeds

Experimental results on the onset of the kink instability of the semiconductor plasma in silicon p+-p-n+ structures are analyzed. The structures were parallelepipeds. The experiments were carried out over the temperature range from 77 to 300 K. The shape of the current-voltage characteristics and that of the threshold curves of the test samples are discussed. The frequency and amplitude of the alternating current which arises as a result of the kink instability are described as a function of the electric field and the magnetic induction at levels substantially above the excitation threshold.

The role of the finite collision duration in femtosecond laser studies of semiconductors

The use of femtosecond laser pulses to excite electron-hole plasmas in semiconductors has become a major method of studying fast processes in this system in recent years. Transition times from the central Gamma valley in GaAs to the satellite X and L valleys are comparable to the reciprocal of the frequency of the phonon involved in these transitions, bringing into question the use of standard perturbation theory approaches. The authors present an initial investigation of the role of retardation arising from the finite collision duration required for such a transition to occur, through the use of a path-integral form of the quantum kinetic equation. A secondary self-scattering process and a probability of completed collisions are used to cast this equation in a semi-classical form.

Exchange effects in hot plasmas in semiconductors

The authors describe a many-body semiclassical approximation for simulating electronic motion. Semiclassical trajectories in this approach are determined from spin-dependent forces and effective mass corrections, which incorporate effects of Heisenberg uncertainty, and the Pauli repulsion and exchange interactions of fermion statistics. The method has been implemented jointly with an ensemble Monte Carlo treatment of phonon scattering, and numerical simulations performed for GaAs. Numerical results indicate that in the femtosecond-scale relaxation of laser-excited plasmas, quantum corrections to the electronic motion will become significant for excitation densities above 2*1018 cm-3.

Propagation of Transverse Electromagnetic Wave Through Magnetized Plasma Slab

The expression for the dispersion relation, Adds and attenuation constant for a magnetized semiconductor plasma slab have been derived. Numerical calculations show that carrier density collision frequency and hall angle significantly affect the attenuation constant.

Stimulated Raman scattering in a magnetized centrosymmetric semiconductor.

By considering the hydrodynamic model of semiconductor plasmas, we performed an analytical investigation of stimulated Raman scattering (SRS) of an electromagnetic pump wave in a transversely magnetized centrosymmetric semiconductor arising from electron-density perturbations and molecular vibrations of the medium both produced at the transverse-optical-phonon frequency. Assuming that the origin of SRS lies in the third-order susceptibility of the medium, we investigated the growth of the Stokes mode. The dependence of the stimulated Raman gain on the external magnetic field strength is reported. The possibility of the occurrence of optical phase conjugation via SRS has also been studied. The steady-state Raman gain is found to be greatly enhanced by the presence of the strong external dc magnetic field.

Collective Behaviour of Photoinjected Plasma in Semiconductors

AbstractThe spectrum of elementary excitations in the nonequilibrium state of a semiconductor under high levels of continuous photoexcitation is studied. Resorting to a quantum transport theory based on the nonequilibrium statistical operator method, the dynamic dielectric response function of the carrier system in the far‐from‐equilibrium steady state is derived, to calculate the Raman scattering spectrum and from it to analyze the spectrum of elementary excitations. Besides the expected bands due to quasi‐particle and collective plasma excitations, the presence is demonstrated of two additional bands associated to low energy excitations and with a linear dispersion relation, and hence termed acoustic plasma modes. The analysis of these two bands points to an interpretation of them as due to the collective motion of the electrons (the ones higher in energy) and of the holes (the ones lower in energy) interacting through the screened Coulomb interaction. At low temperature their lifetimes are mainly determined by dissipative effects mediated by the interaction of the carriers with the radiation recombination field.

Parametric excitation of Alfvén and helicon waves in a magnetoactive compensated semiconductor by microwave radiation.

A theoretical investigation is made on the parametric excitation of electromagnetic Alfv\'en and helicon waves by microwave radiation in a magnetoactive solid-state plasma, viz., compensated germanium. The Krook model has been used to solve the Boltzmann transport equation to find the nonlinear response of electrons and holes in the highly collisional semiconductor plasma. It is noted that the growth rate of excitation of the helicon wave is one order of magnitude higher than that for the Alfv\'en-wave excitation for the same set of plasma parameters. The excitation of the Alfv\'en and helicon waves for parallel propagation is higher than that for the transverse propagation of the incident microwave radiation.

Thermal emission spectrum from a semiconductor electron-hole plasma

Thermal emission spectrum from a semiconductor electron-hole plasma

Some properties of vortices in layered superconducting structures

Some properties of vortices in layered superconductors and superconducting structures with the Josephson interaction between S-layers are studied theoretically. The Josephson vortex lattice is formed in the system if the magnetic fieldH e is parallel to the layers. Long-wave oscillations of this lattice have a sound-like spectrum; the velocity of “magnetic sound” propagating across the layers is small and diminishes with increase ofH e . Using an analogy with electron-hole plasma in semiconductors, we investigate also the behaviour of the layered structure in the fieldH e perpendicular to the layers at temperatures close to the Kosterlitz-Thouless transition temperatureT KT. The spatial dependence ofH(r) and the impedance of the system are determined atT>T KT.

Linear parameters of helical instability in thick silicon wafers at 300 K

An analysis is performed on the dependence of the threshold electric field intensity (Et) of helical instability of a semiconductor plasma on the magnetic induction and threshold frequency on Et at a temperature of 300 K allowing for the form of the volt-ampere characteristic curve of the specimen. It is shown that when the field dependence of the charge carrier concentration in the specimen is taken into account, the variation in the rate of surface recombination and volume lifetime in the process of preparing the specimen, the variation in the path of the threshold curve, and the variation in the field dependence of the threshold frequency are satisfactorily described by helical instability theory for the case of a homogeneous plasma for n ≠ p and μn ≠ μp. The basic cause of incomplete matching of the experimental and theoretical curves is apparently due to not fulfilling the condition on homogeneity of the plasma and the electric field in the presence of the injection of charge carriers from the contacts.

Helical instability of a semiconductor plasma in silicon wafers at 77 K

This paper reports an analysis of the experimental results on how the threshold electric field intensity required to excited helical instability of a semiconductor plasma in wafers of p-silicon depends on the magnitude of magnetic induction. Also cited are data on the dependence of the threshold frequency on electric field intensity. The variations of the amplitude of the alternating current, caused by the development of helical instability, with electric field intensity and magnetic induction well above the instability excitation threshold are examined.

Collision retardation and its role in femtosecond-laser excitation of semiconductor plasmas.

The use of femtosecond laser pulses to excite electron-hole plasmas in semiconductors has become a major method of studying fast processes. The transition times from the central \ensuremath{\Gamma} valley in GaAs to the satellite X and L valleys are comparable to the reciprocal of the frequency of the phonon involved, bringing into question the use of standard perturbation-theory approaches. We investigate the role of retardation arising from the collision duration required for such a transition to occur, through the use of a path-integral form of the quantum kinetic equation. A secondary self-scattering process and a probability of completed collisions are used to cast this equation in a semiclassical form.

Temperature Damping of Plasmons in Nonparabolic Band

Collective excitations influence many effects observed in quantum free-carrier semiconductor plasmas, like, for example, the impurity scattering of carriers for radiation frequencies close to the plasma frequency. Recent studies on linear-conduction-band materials [1, 2] indicate that the free-carrier band nonparabolicity may have a strong impact on the plasmons behaviour. In the present paper the influence of the nonparabolic structure of the free-carrier band on the dispersion of plasmons and their temperature damping is considered. The temperature-dependent formfactor —Im[1/e(q, ω)], where e(q, ω) is the wavevectorand frequency-dependent RPA [3] longitudinal complex dielectric function, is used to examine the properties of the collective excitations. The nonparabolic energy band of the form E(k) = (1/2)[(E8 + 4Ρ2k2)1/2 — Eg] is assumed and the overlap integrals of the electronic wave functions calculated from the Kane model are taken into account in the free-carrier polarizability. The calculations were performed for the plasma in n-PbSe in isotropic approximation [4], with P 2 = ħ2Eg/2m*, where Eg is the energy gap and m* is the effective mass at the bottom of the conduction band. The dielectric function included also the optical-phonon contribution [e.g. 4] i.e. we account for the plasmon-phonon coupling. For the degenerate plasma the nonparabolicity of the free-carrier band was found to extend the range of the wavevectors and energies where the plasmons

Effect of ambipolar diffusion on the hot-carrier relaxation in semiconductors.

The effect of the change in the carrier density due to ambipolar diffusion on the cooling of hot plasmas in semiconductors is investigated. It is shown that the diffusion contributes to a warm-up of the plasma.