F. Lelarge

Organized growth of GaAs/AlAs lateral structures on atomic step arrays: what is possible to do?

Abstract Laterally modulated nanostructures, exhibiting large optical and electrical anisotropy, can be grown on vicinal surfaces. However the lateral organization of Ga and Al atoms is far from ideal. We discuss our way of understanding the growth of these structures.

The building up of terrace periodicity by MBE growth on (0 0 1) GaAs vicinal surfaces

Abstract The morphology of MBE grown GaAs vicinal surfaces is studied using ex situ AFM. Analysing the statistical distribution of terrace width, we succeed in explaining our measurements either by a thermodynamical equilibrium model taking into account the step by step interaction or by a 2D Monte Carlo simulation of the growth. In the latter case, an anisotropic Schwoebel barrier at the step edge has to be introduced in order to get a good agreement. We argue that growth is the efficient process to get a low disordered step array at the usual time scale and temperature range of MBE. In addition the effect of a GaAs AlAs buffer superlattice, or of pure AlAs layer, or of Si doping in GaAs is also discussed.

From low to high field: magneto-transport properties of electron gases in lateral superlattices grown on GaAs vicinal surfaces

Arrays of coupled quantum wires are obtained by growing a lateral superlattice in the channel of selectively doped heterojunctions. Before and beyond the magnetic quantum limit, new phenomena are observed. Our analysis of the low field magnetoresistance and of the quantum transport in the Landau bands gives a consistent value of the lateral potential amplitude.

Towards the optimization of the growth and properties of modulated electron systems on GaAs vicinal surfaces

The growth of quantum structures with strong in-plane 1D potential modulation (amplitude , the Fermi energy of an electron gas in a selectively doped heterojunction) at short scale (periodicity , its Fermi wavelength) relies on the understanding of both the epitaxy and the electronic properties. Some issues such as the morphology of the step array, the organization of the Ga and Al atoms on the surface, and the effect of the electron gas screening or of the tilt of the lateral modulation on the effective potential, are discussed.

Organized growth of GaAsAlAs lateral superlattices on vicinal surfaces: where are the limits?

Abstract We report on three issues concerning the growth of GaAs AlAs lateral superlattices on vicinal surfaces to obtain quantum wires with negligible inter-wire tunnel coupling. We show that the ledge roughness increases with increasing terrace length and decreases for slower growth rates. The tilt angle of lateral superlattices is not the relevant parameter as long as electronic properties are concerned: one has to consider the product of the coverage error by the lateral superlattice thickness. The Ga flux stability is a critical parameter to be controlled. The use of dual-filament cells improves it by a factor two compared to single-filament ones.

Simultaneous Bifurcation Diagrams of Carrier Number and Optical Intensity of External Cavity Laser

We present a simultaneous measurement of the route to chaos of the optical intensity and carrier density as the feedback strength is increased in an external cavity semiconductor laser (ECL).

Organised growth on vicinal surfaces:: segregation and disorder effects

The lateral potential of GaAs/AlAs lateral superlattices (LSL) obtained by organised molecular beam epitaxy is modelled by including segregation effects and step array disorder. This model is compared to experimental data of optical spectroscopy and of thermal dependence of the conductivity anisotropy. The LSL periodicity and amplitude are clearly evidenced in optical spectra whereas the lateral interface abruptness shows up in transport experiments.

Zone–edge optical transitions in GaAs/AlAs lateral superlattices grown on vicinal surfaces by molecular beam epitaxy

Abstract We report on new features in the photoluminescence excitation (PLE) spectra and PLE linear polarization spectra of GaAs/AlAs lateral superlattices grown by molecular beam epitaxy (MBE). These lines appear systematically as the tilt angle of the lateral superlattice is varied. They are identified as zone–edge excitonic transitions by comparison between experimental data and detailed numerical calculations of optical transitions including valence-band mixing and tilt effects.

Enhancement of electron conductivity in GaAs/AlAs coupled quantum wires

Abstract The anisotropy of the low-temperature electrical conductivity of laterally modulated electron gases can be analyzed in a semi-classical approximation, taking into account both the anisotropy of the group velocity which was already considered in previous works and that of the collision time which was ignored so far. By doing so, both components of the conductivity tensor changes with the modulation amplitude, in agreement with our measurements. We predict the possibility of observing, in realistic structures, longitudinal conductivities larger than the Drude conductivity of similar but unmodulated electron gases.

Quantum effects in the electronic conductivity of lateral superlattices

We report a Boltzmann analysis of transport measurements performed on quasi two-dimensional (2D) electron gases with strong in-plane periodic modulation at a short length scale. The quantum scattering anisotropy induced by the periodic potential is included in the calculation and is shown to play an important role in the low-temperature electrical anisotropy. Furthermore, under these conditions the conductivity along the unperturbed direction is no longer given by the Drude formula but is enhanced because of a strong inhibition of the relaxation rate.