Semiconductor Plasma Research Articles

Long-ranged order formation of colloids of implanted ions in a dc biased piezoelectric semiconductor

A dc bias in a piezoelectric semiconductor may drive a beam of electrons which could charge the neutralized colloids of implanted ions and cause a uniform drift of charged colloidal particles. Using a test particle approach and appropriate dielectric-response function for an n-type piezoelectric semiconductor plasma, the potential distribution of uniformly drifting colloidal ions has been investigated. The dynamical oscillatory wake potential, besides the usual static Coulombian Debye–Hückel potential, is found to be contributing more dominantly due to the plasma effect, rather than due to electron–phonon coupling interactions. This periodic wakefield may cause a long-range ordered structure of charged colloidal particles within the semiconductor to exhibit various additional properties.

Laser pulse frequency shifting by ionization and recombination fronts in semiconductor plasma

We present a highly temporally and spatially resolved direct measurement of the propagation of ionization and recombination fronts in bulk ZnSe. The fronts were created by two-photon absorption (TPA) of 10 ps, 800 nm ‘pump’ pulses incident on both sides of a 1 mm thick crystal. The measurement was achieved by the spectral analysis of the frequency shift of a 100 fs ‘probe’ pulse transversely propagating through the crystal at the time of excitation and recombination. The probe was frequency shifted due to the temporal change in the refractive index of the medium. The delay between the probe and the pumps was finely scanned for time-resolved measurements, while imaging of the probe onto a spectrometer slit provided spatial resolution across the crystal. The spatially and temporally resolved shift agrees well with a model that includes TPA and recombination. Our set-up provides a general technique for measurements of rapid ionization and recombination processes.

High-bandwidth terahertz radiation from ponderomotively accelerated carriers using Bessel–Gauss femtosecond pulses

Terahertz generation from high intensity excitation of a semiconductor plasma by a radially polarized Bessel–Gauss femtosecond pulse is modeled. The results are compared with Gaussian pulses of equivalent fluence. Due to carrier confinement, a radially polarized Bessel–Gauss pulse exerts a significantly stronger ponderomotive force on photocarriers than a Gaussian pulse, resulting in an order of magnitude increase in the THz emission power.

Experimental Investigation of Interaction between Electron Beams and Semiconductor Plasma

Experimental Investigation of Interaction between Electron Beams and Semiconductor Plasma

Dispersion and absorption of Alfven wave in ion-implanted group-IV semiconductor

By considering that the implanted ions in a group-IV semiconductor agglomerate to form nanoclusters (NCs) and some of them acquire negative charge, we present an analytical study on excitation and propagation of Alfven wave (AW). Using multi-fluid analysis and Maxwell's equations, a linear dispersion relation for the AW in a semiconductor plasma has been derived. The presence of charged NCs is shown to split the waves into two components and significantly modifying their dispersion and absorption characteristics by creating a charge imbalance in the semiconductor plasma. The NCs, on account of their heavy masses, are assumed to be stationary in the background.

Longitudinal electro-kinetic waves in ion-implanted semiconductor plasmas

A comprehensive investigation of propagation of new longitudinal electro-kinetic modes and novel properties introduced due to presence of negatively charged colloids in semiconductor plasma is presented. By employing the multi-fluid balance equations, a compact dispersion relation for the cases in which wave phase velocity is either larger or smaller than electron thermal velocity is derived. This dispersion relation is used to study wave phenomena and electro-kinetic mode instability numerically. We find important modifications in electro-kinetic branch as well as the existence of new modes of propagation in colloids laden semiconductor plasma. The results of this investigation should be useful in understanding the characteristics of longitudinal electro-kinetic wave in colloids laden semiconductor plasmas whose main constituents are electrons, holes and negatively charged colloids.

Nonequilibrium electron distribution functions in a semiconductor plasma irradiated with fast ions

A kinetic equation for the electrons scattered by acoustic phonons in a solid is derived, and relationships between power-law asymptotic solutions and the particle and energy fluxes in phase space are established. The dependence of the nonextensivity parameter on the intensity of the particle flow in phase space is determined for a nonequilibrium solid-state plasma with sources and sinks. The formation of a steady-state nonequilibrium electron distribution function in a semiconductor with a source and a sink in phase space is numerically simulated using the Landau and Fokker-Planck collision integrals. The nonequilibrium electron distributions formed in the solid-state plasmas of semiconductors and of a Sb/Cs cathode are studied experimentally. It is shown that, within the electron energy range of 5–100 eV, the electron distribution functions decrease with energy according to a power law.

Modified interactions of longitudinal phonon–plasmon in magnetized piezoelectric semiconductor plasmas

A comprehensive investigation of excitation of new electro-acoustic modes and novel properties introduced due to presence of negatively charged colloids in magnetized n-type piezoelectric semiconductor plasma is made analytically. By employing the multi-fluid balance equations along with the elastic and Maxwell's equations, a compact dispersion relation for the cases in which colloidal grains are either robust ( ϑ 0d=0) or dynamic is derived. This dispersion relation is used to study wave phenomena and acoustic mode instabilities analytically. We find important modifications in the acoustic wave branch as well as the existence of new mode labeled as colloids induced acoustic mode in the medium. The results of this investigation should be useful in understanding the properties of interactions of longitudinal phonon–plasmon in colloids laden n-type semiconductor plasmas whose main constituents are electrons and negatively charged colloids.

Quantum magnetic field effects in atom-surface van der Waals interaction

This paper provides the theoretical basis for experimentation on van der Waals atom-surface energy as a manifestation of quantum zero-point energy, with a continuously variable parameterization by a Landau-quantizing magnetic field applied normal to the surface. Quantum magnetic field effects in the second-order van der Waals (vdW) atom-surface energy are fully analyzed. Focusing on the electrostatic nonretarded limit, we employ a random phase approximation (RPA) description of the dynamic, nonlocal polarizability of the mobile semi-infinite Landau quantized plasma behind a semiconductor surface. Our initial examination is carried out using a general low-wave-number approximation of the bounded plasma dielectric function both parallel and perpendicular to the surface, to expeditiously determine quantum magnetic field effects in the second-order vdW energy. Since the formulation calls for an integration over all wave numbers perpendicular to the surface, ${p}_{z}$, we subsequently eliminate the reasonable approximation of the RPA polarizability expanded in powers of ${p}_{z}$, and carry out a more accurate study in this respect. Explicit analytic results for quantum magnetic field effects in vdW energy due to a neutral atom in Coulombic interaction with a semi-infinite nonlocal, dynamic semiconductor plasma are obtained and presented in full detail.

Electron beam fluorescence temperature measurements of N2 in a semiconductor plasma reactor

The rotational temperature of nitrogen molecules in inductively coupled plasma (ICP) discharge has been measured using the electron beam fluorescence (EBF) technique. The neutral gas temperature is an important parameter in understanding the energy balance and neutral radical uniformity in plasma processing. The EBF technique has been used to study rarefied flows, but has not been applied previously to characterize a semiconductor plasma reactor. In this work an electron beam was integrated into an inductively coupled semiconductor plasma reactor, and was used to excite neutral nitrogen molecules from the N2X 1Σg+ state into the excited molecular ion N2+B 2Σu+ state. The electron beam excitation process maps the rotational population distribution of the original ground state into the excited molecular ion state following a dipole model with ΔK=±1. The rotational temperature, which is thought to be equivalent to the neutral gas translational temperature under plasma reactor conditions, can be determined from the rotational intensity distribution of the fluorescence spectrum from the N2+B 2Σu+ state. For the range of neutral gas temperatures found in the plasma reactor a dipole model of the excitation-emission process provides good agreement with the measured spectrum. A least-square fitting procedure comparing the model and measured emission spectra is used to determine the rotation temperature. In this article the first EBF measurements of gas heating in an ICP reactor at different gas pressures (20, 50 mTorr) and plasma source input powers (250, 500, and 1000 W) are reported.

Effect of magnetic field on the thermal nonlinearity of surface waves in plasma-metal structures

A study is made into the effect of the nonlinear mechanism of plasma electron heating on the dispersion properties of potential surface waves propagating along the interface between a metal and finite-pressure magnetoactive plasma. An external steady magnetic field is directed normally to the interface. Different mechanisms of electron energy loss are treated in a weak heating approximation. The energy balance equation is used to determine the spatial distribution of the plasma electron temperature under conditions of nonlocal heating. The effect of the plasma parameters on the nonlinear shift of the wavenumber and on the spatial damping factor of surface waves is investigated. The results obtained are valid for both semiconductor and gaseous plasmas.

Numerical analysis of the relaxation of photoexcited carriers and the hot-phonon effect in GaN

The ultrafast relaxation kinetics of the photo-injected plasma in polar semiconductors has been analyzed with certain details resorting to a first-principles quantum theory based on a nonequilibrium ensemble formalism (the non-equilibrium statistical operator method). Particular attention was given to the so-called hot-phonon effect that accompanies the rapid relaxation processes in the photo-injected plasma. This is done by studying the process of generation and decay of the nonequilibrium longitudinal optical (LO) phonon population per mode. Numerical calculations are presented for the GaN, particular attention being paid to the influence of the carriers effective mass and the time relaxation of the LO-phonons population in the process.

Thermal nonlinearity of potential surface waves at a plasma-metal interface

A study is made of the effect of the heating of plasma electrons in the field of a potential surface wave on the wave dispersion properties. The wave is assumed to propagate along the boundary between a metal and a finite-pressure plasma. Different mechanisms for electron energy losses are considered in the weak heating approximation. The spatial distribution of the plasma electron temperature under nonlocal heating conditions is derived on the basis of the electron energy balance equation. Expressions for the spatial damping rate and the nonlinear shift of the wavenumber are analyzed for different values of the plasma parameters. The results obtained are valid for both semiconductor and gaseous plasmas.

Sensor fault detection in etch based on broadband rf signal observation

To minimize machine downtime in semiconductor plasma etching processes, a sensor fault detection system was developed, employing a broadband rf sensor. The work presented here focuses on detecting errors in the transformer coupled power (TCP) measurement and pressure sensor, though the method has potential for several other sensors. To improve the detection sensitivity, we used real-time machine input estimation, and compared it against actual recipe settings instead of employing the raw rf signals directly. For a main etch process on a Lam TCP 9400SE, ±10% relative deviations in TCP measurement, or ±25% in pressure, can be detected with high accuracy: Detection probability PD≈1 and false alarm rate PF≈0 for both.

Electron–phonon coupling effect on wakefields in piezoelectric semiconductors

Using an appropriate dielectric constant for an n-type piezoelectric semiconductor plasma and a moving test particle approach, it is shown that, besides the usual screened potential, there exists a non-Coulombian oscillatory potential or a wakefield behind a moving charged particle due to a strong resonant interaction between the charged particle and the electro-acoustic mode of the host semiconductor. With the concept of the wakefield, a possible lattice formation of colloids resulting from ion implantation in a current-carrying piezoelectric semiconductor has been examined.

Parametric amplification in magnetized diffusive semiconductor plasmas

Assuming that the origin of the nonlinear interaction lies in the second-order optical susceptibility χ (2) arising from the diffusion-induced nonlinear current density, and using straight-forward coupled mode theory, the parametric amplification is analytically investigated in a magnetized diffusive semiconductor plasma. The threshold value of the pump electric field E 0th is obtained which is found to decrease with rising magnetic field. We found minimum value of E 0th at wave number k=7.45×10 7 m −1 (say k m ). This k m is greatly influenced by carrier concentration and diffusion coefficient of the medium. The parametric gain constant is also obtained. It is found that gain maximizes at very low magnetic field (∼6 kG), which may drastically reduce the fabrication cost of parametric amplifier based on this interaction.

Plasma, thermal, and elastic waves in semiconductors

The system of partially coupled plasma, thermal, and elastic wave equations and conditions for neglecting the coupling between them is analyzed. The treatment considers a semiconductor elastic medium with isotropic and homogeneous thermal and elastic properties. The solution of the coupled system of plasma, thermal and elastic equations is a very complex problem. In most practical cases partially coupled treatment is sufficient. Conditions where it is possible to neglect the coupling between the plasma, thermal, and elastic waves are considered in this work. Special cases for coupled thermal and elastic waves (the thermoelastic problem) and coupled plasma and elastic waves (the electronic deformation) are taken into consideration. An approximate quantitative analysis of the coupling effects is given.

Dynamics of the plasma and thermal waves in surface-modified semiconductors (invited)

Quantitative analysis of ion-implanted layers in Si using the damage-based theoretical modeling and experimental results obtained with the photomodulated reflectance (PMR) technique are described. Our theoretical approach [A. Salnick and J. Opsal, J. Appl. Phys. 91, 2874 (2002)] combines calculations of the ion-induced damage depth profiles in semiconductors with the corresponding scaling of the thermal and carrier plasma wave parameters followed by the calculation of the photothermal response from a multilayered sample. Comparison of the simulated theoretical dose dependencies with experimental PMR amplitude and phase data allows us to study the dynamics of the thermal- and carrier-plasma waves in an ion-implanted semiconductor. The regions of the plasma, thermal, and optical component dominance are defined and the photothermal signal behavior is analyzed in the low, intermediate, and high implantation dose ranges. It is shown that the pump and probe beam wavelengths control the nature of the resulting photothermal signal (thermally or plasma dominated) at low doses while self-annealing effects play a significant role in the photothermal signal behavior at high implantation doses.

Characteristics of TM Surface Waves in a Nonlinear Antiferromagnet–Semiconductor–Superconductor Waveguide Structure

The frequency characteristics of the transverse magnetic (TM) surface waves at mid-infrared frequencies in a layered system, consisting of YBa2Cu3O7−x superconductor film bounded by a nonlinear antiferromagnet (FeF2) cover and a resonant semiconductor plasma (In0.53Ga0.47As) substrate, are fully described. The permeability tensor of the antiferromagnet crystal, for the absence of an applied Zeeman field, has a nonlinear response to the intense rf field. The complex wave number of TM wave is computed by solving the dispersion equation in order to determine the effects of the superconductor and resonant semiconductor on the dispersion characteristics for both the reduced phase and reduced attenuation constants as a function of the temperature and frequency. The power flow through the waveguide structure has also been investigated. We have found that superconductors have the ability to reduce the propagation losses. We have also found that the reduced attenuation constant is highly dependent on the temperature of the superconductor.

The Perturbative Treatment of the Equation of State in Clustered Many-Particle Systems

Electron–hole plasmas in semiconductors, electron–ion plasmas or nucleonic matter are examples for many-fermion systems. Their quantum-statistical treatment will be performed using a thermodynamic Green function approach. The formation of bound states can be considered within a chemical picture. However, we will show that the systematic perturbative treatment of the self-energy seems to lead to the occurrence of a singularity. This can be resolved by considering the broadening of the bound state energy levels. Thus, it is possible to unify different approaches such as the model of the partially ionized plasma and the averaged atom model.