Benjamin Lax

Bio: Benjamin Lax is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Cyclotron resonance & Laser. The author has an hindex of 31, co-authored 125 publications receiving 4616 citations.

Temperature Dependence of Raman Scattering in Silicon

Abstract: We have measured the linewidth and the frequency of the q=0 optical phonon in silicon over the temperature range of 20-770\ifmmode^\circ\else\textdegree\fi{}K. The temperature dependence of the linewidth has been interpreted as arising from the decay of the optical phonon to two LA phonons at half the optical frequency. From the observed temperature variation, we deduce an absolute half-width $\ensuremath{\Gamma}$ of 2.1 ${\mathrm{cm}}^{\ensuremath{-}1}$ at 0\ifmmode^\circ\else\textdegree\fi{}K. This value is considerably smaller than that obtained theoretically by Cowley on the basis of numerical calculations which include decay to phonons throughout the Brillouin zone. His numerical calculations also predict a temperature dependence of the linewidth which does not agree with experiment. However, the observed change in frequency with temperature correlates very well with Cowley's theory. We have also studied the relative intensities of Stokes and anti-Stokes components of Raman spectra. The observed temperature dependence of the relative intensities is compared with that predicted on the basis of the Bose-Einstein population factor for the optical phonon.

Theory of Optical Magneto-Absorption Effects in Semiconductors

Abstract: The theory of the effect of a magnetic field on the optical absorption in semiconductors is developed on the basis of the effective-mass approximation. For simple parabolic conduction and valence bands and a direct transition which is allowed at k=0, absorption peaks occur at energies above the zero-field gap. Since the selection rule for the transition is $\ensuremath{\Delta}n=0$ where $n$ is the magnetic quantum number, the spacing between the peaks is the sum of the cyclotron frequencies for the two bands. For degenerate band edges, the spectrum is more complicated. A detailed treatment of the direct transition in germanium is given in which account is taken of the change in curvature of the bands away from k=0 and the results are in good agreement with the experimental measurements of Zwerdling, Lax, Roth, and Button. The k=0 conduction band mass is found to agree with predictions based on cyclotron resonance in the valence band. In addition, a gyromagnetic ratio for conduction electrons of -2.6 resulted from the calculations. The deviation from $g=2.0$ is due to spin-orbit interaction. In InSb the effect is much greater, the result being $g=\ensuremath{-}50$. These are consistent with experimental results. For bands in which the transition probability vanishes at k=0, absorption peaks will also occur corresponding to $\ensuremath{\Delta}n=\ifmmode\pm\else\textpm\fi{}1$ but absorption edges occur for $\ensuremath{\Delta}n=0$. In the case of indirect transitions, the absorption does not exhibit oscillations but consists of a series of "steps" as has been observed in Ge by Zwerdling, Lax, Roth, and Button.

High magnetic fields

Abstract: : Some 85 of the papers prepared for the first International Conference on High Magnetic Fields are published in this volume. These reports cover the most significant present work on the generation and use of very high or very special magnetic fields, including new solenoid designs for pulsed or continuous operation, developments in cryogenics, new generators and power supplies, new cooling systems for continuous-field coils, analyses and fabrication experiments on superconductive compounds and rare-earth alloys, continuing attacks on plasma-containment problems arising in controlled thermonuclear fusion research, and studies magnetic-shielding-system parameters for the protection of space travellers against high-energy radiation. The four parts of this volume cover: designs of high-field solenoids and supporting systems, high-field research programs now underway at laboratories around the world, application of high fields in solid-state and low-temperature physics, and use of high fields in plasma physics. References at the end of each paper constitute in sum the most complete bibliography of the field yet compiled.

Transient Response of a p‐n Junction

Abstract: The authors investigate the transient response of a p‐n junction in a circuit where the applied voltage is suddenly switched from the forward to the reversed direction. The behavior is studied as a function of the circuit resistance. The solution of the appropriate diffusion equation is carried out for a time‐dependent boundary condition, resulting in an integrodifferential equation. Analytical and numerical results for the current and the junction voltage as a function of time are then obtained by suitable approximations for the ``recovery'' and reverse periods. The ``recovery'' or reversal time tf is the time required for the junction voltage to become negative and is given by erftfτ=11+(If/Ir), where τ is the lifetime of holes, If is the forward current, and Ir the initial reverse current, which is limited by the external resistance.

Semiconducting and other major properties of gallium arsenide

Abstract: This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...

Electro-optics of perovskite solar cells

Abstract: Measurements reveal the exciton binding energy, dielectric constant and refractive index of planar perovskite solar cells.

Localization: theory and experiment

Abstract: The transport properties of disordered solids have been the subject of much work since at least the 1950s, but with a new burst of activity during the 1980s which has survived up to the present day. There have been numerous reviews of a more or less specialized nature. The present review aims to fill the niche for a non-specialized review of this very active area of research. The basic concepts behind the theory are introduced with more detailed sections covering experimental results, one-dimensional localization, scaling theory, weak localization, magnetic field effects and fluctuations.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

Abstract: It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.