J.F. Palmier

dc and microwave negative differential conductance in GaAs/AlAs superlattices

Negative differential conductance (NDC) at 300 K in n+‐nn+‐GaAs/AlAs superlattice structures biased perpendicularly to the layers is demonstrated, and shown to be strongly enhanced at microwave frequencies close to the inverse transit time of electrons. The deduced electron velocities are in fair agreement with those independently determined in undoped superlattices where NDC was inhibited by the electric field nonuniformity. From the analysis of the experimental data, we show that NDC is a bulk superlattice effect, not related to ‘‘quantum defects,’’ e.g., enlarged barriers.

High-field perpendicular conduction in GaAs/AlAs superlattices

Miniband conduction in undoped GaAs/AlAs superlattices (SLs) has been investigated through current‐voltage measurements on n+‐SL‐n+ structures. From the comparison with simulations based on an effective medium approximation for the conduction through the superlattice, we directly obtain the field dependence of the electron velocity perpendicular to the layers. Our data show strong evidence of negative differential velocity in a 35.5/20 A (well/barrier width) SL.

A Monte Carlo simulation of silicon nitride thin film microstructure in ultraviolet localized-chemical vapor deposition

Abstract Microstructural changes of surfaces and bulk of a SiN: H were investigated at the atomic level by a simulator. The simulator is based on a solid-on-solid type model for ultraviolet localized-chemical vapor deposition. The calculations consider the well-defined photolysis products adsorbed at atomic sites. Incorporation of main species is enabled by a Monte Carlo-Metropolis simulation technique. Photodeposition rates are obtained using bond dissociation energies. In this manner, the dependence of root-mean-square deviation of surface roughness and bulk porosity on operating conditions can be predicted. Photonucleation and photodeposition with a UV low pressure mercury lamp at low pressure and temperature were simulated onto indium phosphide substrate.

Microwave miniband NDC in GaInAs/AlInAs superlattices

Abstract The negative differential conductance originating from electron Bragg scattering in miniband transport is demonstrated in a series of five GaInAs/AlInAs superlattices having miniband width from 18 to 81 meV. Sharp resonances or broad-band amplification (0–55 Ghz) are obtained according to the miniband width. Experimental values of the peak velocities deduced from the microwave resonances, and, to some extent, the d.c. values, are satisfactorily compared with semi-classical theory based upon the complete Boltzmann Transport Equation.

Miniband conduction and electron heating in semiconductor superlattices through time-of-flight experiments

We investigate the nonlinear conduction mechanisms of electrons in a semiconductor superlattice miniband. Experimental results obtained from time-of-flight measurements in GaAs/AlAs superlattices are compared with analytical semiclassical approaches. It is shown that the peak velocity can be accounted for when electron heating is assumed to take place. The dynamics of electron transport is also investigated by numerically solving the time-dependent Boltzmann equation including polar optical phonon and interface roughness scattering.

Transverse magnetotransport anisotropy in a semiconductor superlattice

The vertical magnetotransport properties of GaAs–AlAs superlattices have been investigated as a function of the in‐plane magnetic field orientation. Two main effects were observed: (i) the influence of the roughness anisotropy with respect to the crystallographic orientation, and (ii) the nonparabolicity of the energy in the plane of the layers. The interface fluctuations induced a modulation of the miniband transport with a period of 180°. The nonparabolic energy of the deflected electronic orbits also induced a modulation of the vertical transport but with a period of 90°. Both observed effects are in qualitative agreement with a semiclassical description of the Boltzmann transport equation.

Atomistic comparative study of VUV photodeposited silicon nitride on InP(100) by simulation and atomic force microscopy

Abstract We report on an accurate validation of a new Monte Carlo three-dimensional model. Simulations up to 1200 A layer thickness have been carried out for amorphous thin film layers of SiN:H deposited at low temperature (400–650 K) on (100) InP, by vacuum ultraviolet (VUV, ∼185 nm)-induced chemical vapor deposition (CVD). The computer simulations in the mesoscopic-submicronic range are compared with atomic force microscopy and index of refraction measurements. The reconstituted surface roughness and the voids discrete representations of the bulk are found to be in good agreement with these measurements. Simultaneously at around 450 K (at ∼175°C), thermal characteristic evolution of the both surface roughness and bulk porosity showed a transition from rough to smooth deposition and from low to high density.

Negative differential perpendicular velocity in GaAs/AlAs superlattices

Abstract We investigate the doping level, hydrostatic pressure, temperature and superlattice parameter dependence of the perpendicular negative differential velocity (NDV) of GaAs/AlAs superlattices. The results show that NDV is a single Γ miniband effect. A qualitative agreement is found with Esakis negative effective mass model, although a few limitations of this model are pointed out and some improvement is suggested.

Negative differential conductance frequency resonances in X valley superlattice minibands

Electron transport along the growth axis of a series of slightly indirect GaAs/AlAs superlattices (SL) is experimentally investigated. Our results, based on current‐voltage and frequency resonance measurements in agreement with calculated characteristics, reveal unambiguously the existence of negative differential velocity at 80 K. Miniband transport in the lower Xxy miniband appears to explain this effect, owing to the low effective mass of Xxy states along the quantization axis.

Dynamics of 3D representation of interfaces in UV-induced chemical vapor deposition: experiments, modeling, and simulation for silicon nitride thin layers

We study the surface dynamics of silicon nitride films deposited by UV-induced low pressure chemical vapor pressure. Atomic force microscopy measurements show that the surface reaches a scale invariant stationary state coherent wit the Kardar-Parisi-Zhang (KPZ) equation. Discrete geometry techniques are oriented to extra morphological characteristics of surface and bulk which corresponds to computer simulated photodeposit. This allows to determine the physical origin of KPZ scaling to be al ow value of the surface sticking probability, and connected to the surface concentration of activate charged centers, which permits to start the evaluation of the Monte Carlo-molecular dynamics simulator.