Showing papers by "Jens H. Schmid published in 2002"

Surface morphology of GaAs during molecular beam epitaxy growth: Comparison of experimental data with simulations based on continuum growth equations

Abstract: Using atomic force microscopy and in situ elastic light scattering we show that the surface of molecular beam epitaxy ~MBE! grown GaAs tends towards an equilibrium roughness independent of the initial condition, as predicted by kinetic roughening theory. Two separate continuum growth equations are consistent with the observed equilibrium roughness, namely, the Kardar-Parisi-Zhang ~KPZ! equation ]h/]t5n„ 2 h1(l/2) 3(„h) 2 1h, where h is the surface height and h represents nonconservative noise, and the MBE equation ]h/]t52k„ 4 h2(L/2)„ 2 („h) 2 1h c , where h c represents conservative noise. These equations represent different physical smoothing mechanisms, so to distinguish between them we have numerically solved both equations. A novel geometric implementation of the nonlinear terms avoids instabilities associated with stiffness of the equations. We find that the time and length scale dependence of the smoothing of initially rough substrates is consistent with the KPZ equation but not the MBE equation. As the growth temperature is increased the coefficient n increases relative to l, but the KPZ description remains valid over the entire measured temperature range of 550‐600 °C. Reducing the As overpressure increases the anisotropy of the surface morphology. We provide a physical interpretation of the KPZ equation in which the incorporation rate of mobile adatoms on the surface is governed by evaporation/condensation type dynamics. These results provide important insight into the MBE growth mechanism of GaAs.

Comparison of strain relaxation in InGaAsN and InGaAs thin films

Abstract: We compare the strain relaxation of In0.08Ga0.92As and In0.12Ga0.88As0.99N0.01 epitaxial thin films grown on GaAs (001) by elemental-source molecular-beam epitaxy. The epilayers we studied were essentially identical in their compressive lattice mismatch (0.62±0.02%), and thickness (600 nm). The strain state of the samples was determined by in situ substrate curvature monitoring, and by ex situ x-ray diffraction and plan-view transmission electron microscopy. We observe a slower rate of strain relaxation, and a 25% higher residual strain in the nitride. This is attributed to the presence of nitrogen interstitials in the InGaAsN epilayers and/or to the higher nitrogen bond strengths.

Kinetic roughening of GaAs(001) during thermal Cl 2 etching

Abstract: The surface morphology of ${\mathrm{Cl}}_{2}$-etched GaAs(001) is measured as a function of etch time by atomic force microscopy and elastic light scattering. A flat surface is found to become rougher during the etch whereas a textured substrate becomes smoother. We have numerically simulated this behavior. It is found that the evolution of surface roughness at length scales between 50 nm and $5 \ensuremath{\mu}\mathrm{m}$ can be described with excellent accuracy by a continuum equation for the surface height $h(\stackrel{\ensuremath{\rightarrow}}{x},t),$ which is given by $dh/dt=\ensuremath{ u}{\ensuremath{ abla}}^{2}h\ensuremath{-}\ensuremath{\lambda}/2(\ensuremath{ abla}{h)}^{2}\ensuremath{-}K{\ensuremath{ abla}}^{4}h+\ensuremath{\eta},$ where $\ensuremath{\eta}$ is a random noise input.

Surfactant enhanced growth of GaNAs and InGaNAs using a Bi flux

Abstract: InGaNAs containing a dilute amount of nitrogen is a promising new material for fabricating optoelectronic devices in the 1.3 - 1.55 /spl mu/m wavelength range on GaAs substrates, in particular as the active material for vertical cavity surface emitting lasers. Recent edge-emitting InGaNAs lasers have demonstrated an improvement in both threshold currents and characteristic temperatures over those of an InP based reference laser. A flux of bismuth was applied during the growth of InGaNAs quantum wells and bulk GaNAs layers by elemental source MBE.