Semiconductor Plasma Research Articles

Cleaning and Doping of Silicon in a BF3Plasma during Fabrication of Ohmic Contacts

The formation of reliable ohmic contacts to silicon is considered. Silicon surface cleaning, contact window doping, and molybdenum application by cathode sputtering in the BF3atmosphere are carried out in a single vacuum cycle. A model of semiconductor–plasma and dielectric–plasma contacts under stationary discharge conditions is discussed. It is shown that the rates of processes with the participation of charged particles on p-Si and n-Si surfaces substantially differ. The resistivity of Mo-n + Si and Mo-p + Si contacts is the least when the molybdenum films are applied by sputtering in the Ar + (10–15) vol % BF3atmosphere.

Quasi-hydrodynamic modelling and computer simulation of coupled thermo-electrical processes in semiconductors

The quasi-hydrodynamic model for semiconductor devices is a typical example of non-local models which, in contrast to the conventional drift-diffusion models, allows to account for non-equilibrium processes in semiconductor plasma. In this paper, we present results of a numerical simulation of semiconductor devices using the quasi-hydrodynamic model. The results have been obtained with the package SCSIMU, a C++ based program in which efficient exponential difference schemes for the quasi-hydrodynamic model have been implemented. Algorithmic procedures and modelling of realistic semiconductor devices such as ballistic and PIN diodes are discussed with numerical results.

Optical properties of semiconductors via pump-probe experiments:statistical-thermodynamical approach, hot plasma and coherent phononstates

We present an analysis of the nonequilibrium thermodynamics and, mainly, aresponse function theory for the study of optical properties inultrafast-spectroscopy pump-probe experiments. These experiments give rise tothe formation of a photoinjected plasma in semiconductors infar-from-equilibrium conditions. The dissipative processes that evolve in thismedium greatly influence optical and transport properties. The theory is centredon the application to the study of the phenomenon of modulated changes in thetime-resolved reflectivity spectrum. In particular, we show that this phenomenonconsists in the coupled effect of coherent-LO-phonon and carrier-charge-densitymotions, which are driven through the action of the coherent photons of thelaser electromagnetic radiation. In the given conditions the modulation effectdecays in time and has associated a frequency close to the zone-centre upper LOphonon-optical plasma hybrid mode, as experimentally observed.

Nonlocality effects of a bulk semiconductor plasma in interaction with quantum well superlattice plasmons

An explicit closed form determination of the inverse dielectric function for an N-sheet two-dimensional (2D) electron superlattice embedded in a nonlocal bulk host semiconductor plasma is presented here, as well as for an infinite superlattice. The coupled plasmon dispersion relation is analyzed for the model in which the 2D quantum wells constituting the superlattice have just one occupied subband and the bulk plasma of the host has hydrodynamic nonlocality. Nonlocal corrections are obtained for a hybrid superlattice plasmon in interaction with the host bulk plasmon. In addition, we find that this model predicts a new nonlocal low-frequency mode.

Interaction between microwave oscillation and a photoionized semiconductor plasma in a two-layer waveguide

Theoretical studies are performed on the interaction between microwave electromagnetic radiation and a photoionized semiconductor plasma in a two-layer waveguide. The interaction between the characteristic wave types of oscillation and a photoexcited semiconductor plasma is investigated. The dependences of the reflection coefficient and phase of the microwave-frequency wave on the optical radiation intensity are obtained; the effect of the surface and of the geometric dimensions of semiconductor elements on these parameters is investigated.

Possible lattice formation of new materials within a piezoelectric semiconductor plasma

The possible lattice formation of grains of chosen material in a magnetized current carrying n-type piezoelectric semiconductor plasma has been examined. In addition to the repulsive Coulomb potential, there appears a non-Coulombic oscillatory potential among the highly charged grains due to the strong resonant collective interaction of the grains and the electron-acoustic mode of the host semiconductor giving rise to the possibility of the lattice formation of grains of new materials.

On large time asymptotics for drift-diffusion-poisson systems

In this paper we analyze the convergence rate of solutions of certain drift-diffusion-Poisson systems to their unique steady state. These bi-polar equations model the transport of two populations of charged particles and have applications for semiconductor devices and plasmas. When prescribing a confinement potential for the particles we prove exponential convergence to the equilibrium. Without confinement the solution decays with an algebraic rate towards a self-similar state. The analysis is based on a relative entropy type functional and it uses logarithmic Sobolev inequalities.

Nonlinear-driven instability of dynamical plasma in solids: Emergence of spatially self-organized order and chaotic-like behavior

We analyze in detail the nonlinear kinetics of a carrier system in a photoinjected plasma in semiconductors under the action of constant illumination with ultraviolet light. We show that the spatially homogeneous steady-state becomes unstable, and a charge density wave emerges after a critical intensity of the incident radiation is achieved. It is shown that this instability can only follow in doped p-type materials. In bulk systems the critical intensity was found to be too high making the phenomenon not observable under realistic experimental conditions. However, a more efficient electron excitation can be obtained in low dimensional p-type systems, like some molecular and biological polymers, where the interaction may follow by chemical interaction with the medium. We show that for intensities beyond the critical threshold an increasing number of modes provide further contributions (subharmonics) to the space inhomogeneity. It is conjectured that this process could lead the system to display chaotic-like behavior.

ＣｌＦ３ガス等方性ドライエッチングのマイクロマシニングへの応用研究

Within the micromachining field, which is based on semiconductor manufacturing technology, wet etching and plasma etching are generally used as the isotropic etching for producing movable parts on silicon wafer. However, these methods have the following disadvantages. 1) Wet etching; (1) Dynamic damage such as surface tension occurs, (2) It is difficult to perform in-line etching, 2) Plasma etching; (1) Thermal damage due to plasma, (2) Detoxication at high-temperature is required. To solve them, it is proposed a new isotropic dry etching using CIF, gas. The following results are obtained experimentally; (1) Si can be etched isotropically by CIF3 gas at room temperature and atmospheric pressure, (2) Ni film electroplated and Cr film sputtered are useful as makes for CIF, gas dry etching, (3) Ni rotor electroplated on Si could be released by the proposed CIF3 gas etching.

A Fortran code for solving the Kadanoff–Baym equations for a homogeneous fermion system

A Fortran code for solving the Kadanoff–Baym equations for a homogeneous fermion system is presented. These are a class of quantum kinetic equations the solutions of which are two-time Green (correlation) functions, which carry both statistical (orbital occupation distributions) and dynamical (orbital energies and widths) information about the system away from equilibrium. In this program, the system's initial state is assumed to be uncorrelated. As examples of applications, two separate situations involving equilibration (thermalization) are considered: the first one models an electron plasma in an excited semiconductor, and the other models nuclear heavy-ion collisions. The most time-consuming part of the program is the computation of the convolutions of various combinations of the Green functions. This task is efficiently performed by the use of Fast Fourier Transform. As summary output, the particle density, energy densities, and the quadrupole moment of the distribution are displayed. The program can easily be modified such that the user may use any initial distribution of fermions.

Scattering of a surface plasmon polariton by rapid plasma creation in a semiconductor slab

The scattering of a surface plasmon polariton in a semiconductor slab by rapid plasma creation in the slab is explored. As a result of the scattering, the initial surface wave breaks up into two frequency-upshifted surface waves propagating in opposite directions along the slab and generates a static magnetic field and a dc inside the slab and transient radiation that escapes the slab. A part of the initial energy can also be trapped inside the slab owing to total internal reflection and forms frequency-upshifted guided modes of the slab. The scattering of a surface wave by a rapidly created plasma allows the analysis of basic processes that occur in nonstationary media in the presence of boundaries. The practical applications include the control of propagation of guided radiation in integrated optics devices, coupling the radiation out of waveguides, and ultrafast transient spectroscopy of an electron–hole plasma in semiconductors.

Modelling and computer simulation study of laser‐plasma interaction in semiconductor

Computer simulations were done extensively in order to study non‐linear dynamics of laser‐plasma interaction in InSb semiconductor. We constructed the modified Duffing kind of non‐linear semiconductor plasma oscillator equation. Collision frequency is found to be dominant parameter to influence the bifurcation, chaos, hysteresis and bistable effects of plasma wave. Small windows of higher period cascade above the critical value of laser parameter (α1α2) in the chaos region are observed. Laser‐plasma exhibits too much chaotic regime at lower value of laser driving frequency (δ). Hysteresis and bistable regions of plasma wave are presented and the conditions for their occurence are identified. The unstable regions completely merge at higher value of effective collision frequency (γ).

Skin effect during propagation of high-power short-wavelength microwaves in a partially ionized semiconductor plasma

A study is made of the propagation of high-power electromagnetic waves in spatially inhomogeneous plasmas of thin semiconducting elements and films. The effect of surface recombination and an external magnetic field on the depth of penetration of an ionizing field into the semiconductor plasma is examined.

T-matrix approach to equilibium and nonequilibrium carrier-carrier scattering in semiconductors

An analysis of strong-coupling effects in carrier-carrier scattering in electron-hole plasmas in semiconductors is presented. The conventional approach to scattering and dephasing rates is based on the Born approximation (a scattering cross section proportional to the square of the dynamically screened interaction potential), and is strictly valid only in the limit of the weakly coupled quantum plasma. Otherwise, strong correlations are expected to become important in the scattering quantities. Therefore, we perform a thorough analysis of scattering rates in the framework of the statically screened T-matrix (ladder) approximation. We solve the two-particle Schr\odinger equation and provide explicit results for the carrier-carrier scattering rates in equilibrium as well as for optical excitation conditions. Numerical results for GaAs show evidence of significant deviations from the common Born approximation. Finally, dynamic screening effects are included approximately.

Electron Distribution Function in a Nonideal Plasma in Strong Electric and Laser Fields

AbstractUsing a two‐term approximation to the kinetic equation, the generalized electron energy and momentum distribution which governs the electron transport and rate properties in nonideal plasma is analyzed. A class of general solutions of the equation is found in the model case which is widely used in semiconductor plasma. An equation that generalizes the well‐known Zeldovich‐Raizer quantum kinetic equation in the case of nonideal plasma is deduced. Explicit nonequilibrium solutions of this equation for the electron energy and momentum distribution function in a strong laser field are constructed.

Frequency up-conversion and trapping of ultrashort laser pulses in semiconductor plasmas

It is shown that the interaction of ultrashort laser pulses with nonstationary semiconductor plasmas can, under appropriate conditions, lead to a variety of interesting phenomena including controlled upshifting of the laser frequency, leading to the possibility of tunable lasers in a wide range of frequencies, and trapping (nonpropagation) of a substantial part of the incident pulse.

Magnetic-field effect on wave dispersion in a free semiconductor plasma slab

An investigation of wave propagation in a plasma slab bounded by dissimilar dielectric media has been made numerically in the magnetohydrodynamic approximation. It has been shown that four families of waves can propagate: plasma, cyclotron, anisotropic and waveguide modes. It has been proved that singular waves propagate at the crossing points of the waves with a complex zone boundary. We have analysed the influence of the bounding dielectric media, the width of the waveguide and the magnetization of the plasma on the spectrum of the waves. The distributions of the fields, the energy density and the Poynting's vector of different modes along the dispersion curves have been analysed. The passing of energy from dielectric to plasma with increasing wavenumber has been shown.

Ultrafast photodetectors based on the interaction of microwave radiation and a photoexcited plasma in semiconductors

The interaction of microwave radiation with the plasma in photoionized semiconductor photocells (CdS, CdSe) placed in waveguide measurement systems is investigated theoretically and experimentally. The interaction of the characteristic waveguide modes with a photoexcited semiconductor plasma is investigated. The dependence of the reflection coefficient and phase of the microwave radiation on the intensity of the optical radiation to be measured is obtained, and the influence of the surface of the semiconductor photocells on these parameters is investigated. A microwave photodetector design based on a millimeter-wave interferometer is developed.

Excitation of electrostatic waves at the beat frequency of two laser beams in a semiconductor plasma

A theoretical investigation has been made of the parametric excitation of electrostatic waves at the beat frequency of two high-power, collinear, uniform laser beams in a highly collisional, magneto-active, compensated semiconductor plasma. The gyro-kinetic approach has been employed to find the linear and nonlinear response of electrons and holes in this semiconductor plasma. It is found that for typical plasma parameters in compensated Ge, two collinear laser beams of equal power density, 2.37 MW cm-2, can excite beat waves of power density 1 kW cm-2. The effects of electron-phonon collision frequency (v), transversely applied external magnetic field (B0), plasma density (n0), and variation of the effective mass of electrons and holes on this parametric excitation process in a semiconductor plasma are discussed.

Simulation Study of Plasma Wave Generation and Nonlinearity in InSb Semiconductor

It is shown that the large amplitude plasma were driven by two collinear laser beams in InSb semiconductor exhibit bistability and hysteresis studied by computer simulation. The influence of collision, laser parameter and frequency mismatch were considered for the large amplitude plasma wave and transition to chaos and leading to plasma wave breakdown. It is confirmed by bifurcation diagram and poincare map. The laser pump strength parameter rather greater than critical value leading to the occurrence of bistability (instability) region. The results may be relevant to beat-wave current drive in Tokamak devices and to beat-wave particle accelerator in semiconductor plasma.