Ramon U. Martinelli

2.7‐μm InGaAsSb/AlGaAsSb laser diodes with continuous‐wave operation up to −39 °C

We have demonstrated continuous wave operation of 2.7‐μm InGaAsSb/AlGaAsSb multiquantum‐well diode lasers up to a temperature of 234 K (−39 °C). These devices were grown by molecular‐beam‐epitaxy. They have a tendency to operate in a dominant single mode over well‐defined temperature and current intervals. A comparison of spontaneous emission spectra shows that above threshold, the quasi‐Fermi level is pinned and that most of the carriers are injected into nonlasing states. This effect leads to a rapid decrease of differential efficiency with increasing temperature.

Electron transport and emission characteristics of negative electron affinity AlxGa1−xAs alloys (0≤x≤0.3)

Photoemission and secondary‐emission measurements were made from AlxGa1−xAs (x=0, 0.1, 0.2, and 0.3) surfaces which were activated to negative electron affinity (NEA) using Cs and O2. Values for the diffusion length L and the surface escape factor B were determined from the data for each alloy composition. It was found that B decreases with increasing AlAs composition and that the diffusion lengths for all the alloys examined were at least 6.0 μm.

Solution of the non-linear Poisson—Boltzmann equation in the interior of charged, spherical and cylindrical vesicles. I. The high-charge limit

Abstract Solutions are obtained for the truncated Poisson—Boltzmann (TPB) equation, valid for high surface charges, in the interior of charged cylinders and spheres. The solution for the cylinder is analytic, for the sphere numerical. For the sphere a simple polynomial algorithm is presented which can approximate the exact solution to any desired accuracy. A plot of various physical quantities is given for vesicles of inner radii 150 and 500 A, respectively. For each geometry a single universal function exists which can accommodate any value ψ0 for the potential ψ at zero radius. The potential ψ is singular at the radius r∞′ related to ψ0 through: r∞′ = r∞ exp(−ψ0/2), where ψ(r∞) = ∞ for ψ0 = 0.

Improved transmission secondary emission from InxGa1−xP/GaAs self‐supporting films activated to negative electron affinity

Transmission secondary emission (TSE) gains as high as 540 at primary energies of 20 keV have been achieved in self‐supporting InxGa1−xP/GaAs structures activated to negative electron affinity (NEA). Furthermore, a linear dependence of the gain on primary energy has been obtained in the range 4–20 keV. These improvements result from the long diffusion lengths (L) in the GaAs and the low interfacial recombination velocities (sb) at InxGa1−xP/GaAs interfaces which have small smounts of lattice mismatch (e<3×10−3). Secondary emission yield curves along with corresponding cross‐sectional transmission electron microscope micrographs from structures with lattice mismatches of 0, 3×10−3, and 1.2×10−2 are presented. Evidence from highly mismatched structures suggests that high densities of inclined dislocations degrade L and sb. Reflection secondary emission data support these conclusions.

Monte Carlo studies of hot‐electron energy distribution in thin insulating films. I. Constant mean free path and a one‐dimensional simulation

The hot‐electron energy distribution produced in a high electric field F across a thin insulating film is studied by Monte Carlo calculations on a digital computer. The dominant electron collisions are assumed to be those with the lattice, producing single optical‐phonon emissions of energy eph. The mean free path λ is taken as a constant independent of energy, and both isotropic and anisotropic scattering are studied. A scaling law for the average electron energy Eave,ss in the steady‐state distribution, previously found analytically for isotropic scattering, namely, Eave,ss=k (Fλ)2e/ph, is found to hold also for anisotropic scattering, k being a numerical constant determined by the detailed nature of the scattering law. Forward scattering produces larger values of k, backward scattering smaller values. No matter how strongly peaked the forward scattering, short of exact (ϑ=0) forward scattering, there is a finite steady‐state distribution. An analogous scaling law is found for the development distance D...

Buffering of charge by the Coulomb condensate in non-linear Poisson-Boltzmann theory

Abstract Numerical integration of the non-linear Poisson-Boltzmann equation, for both spherical and cylindrical geometries, exhibits the well-known condensation phenomenon. This Coulomb condensate very strongly buffers the charged surface from the “distant”, bulk electrolyte.

Monte Carlo studies of hot‐electron energy distributions in thin insulating films. II. Energy‐dependent mean free path and instability

Monte Carlo calculations are used to study theoretically hot‐electron transport through a thin insulating film subjected to a high uniform electric field F. A constant energy‐independent mean free path λ leads to a stable steady‐state energy distribution for the electrons, characterized by an average steady‐state energy Eav,ss. Eav,ss depends on λ, F, and eph, the optical phonon energy associated with scattering of the hot electrons by the lattice. An energy‐dependent mean free path λ (E), which increases with increasing electron energy, can lead to energetic runaway of either a relatively small number of electrons in the distribution (quasistability or a bimodal distribution) or the entire distribution (instability). A graphical method has been developed to gain insight into this problem. The method rests on an analysis of the intersections of two curves plotted in the E‐λ plane, one curve being the plot of Eav,ss versus λ, where λ is the mean‐free‐path parameter taken to be constant (energy independent)...

Secondary electron emission from the GaN:Cs–O surface

High secondary emission ratios have been obtained for the GaN:CsO surface. A peak ratio of 51 at 3 keV primary electron energy has been observed. At 20 keV the ratio is 24, compared with 2 when the GaN is uncesiated. Analysis of the data indicates that the diffusion length in the material is between 300 and 800 A, and the surface escape probability for secondary electrons is 0.36. These results indicate that the GaN:CsO surface has been activated to negative electron affinity (NEA).

Some Effects of Nonuniform Pumping on the Mode Structure of Solid State Lasers

The effects of nonuniform pumping upon the structure of near‐axial low‐order transverse modes of a laser cavity are considered. For transverse variations of the pumping level, the mode profiles may be severely distorted. The primary cause of the distortion arises from the spatial variation of the anomalous dispersion term in the dielectric constant associated with the laser line. Modes on the high‐frequency side of the line center are distorted in such a way as to increase their gain relative to modes lying on or below line center. The results show that mode profile distortions are significant for pumping level variations of a few percent.