Jens H. Schmid

Surfactant enhanced growth of GaNAs and InGaNAs using bismuth

Dilute nitride GaNAs thin films and InGaNAs single quantum wells (QWs) have been grown by molecular beam epitaxy with a concurrent bismuth flux. Bi does not incorporate into the films and acts as a surfactant. Atomic force microscopy images reveal that, at sufficiently high bismuth flux, step flow growth occurs in GaN0.004As0.996 even at substrate temperatures as low as 4601C. This results in an order of magnitude decrease in the surface roughness. A similar smoothing effect is obtained when growing GaAs and AlGaAs thin films with bismuth. Furthermore, Bi is found to enhance the incorporation of nitrogen into GaNAs. The peak photoluminescence intensity from an In0.26Ga0.74N0.011As0.989 QW is increased by more than a factor of two with the surfactant. We conclude that Bi reduces the incorporation of defects and/or impurities in the dilute GaNAs based alloys. r 2002 Elsevier Science B.V. All rights reserved. PACS: 81.15.Hi; 68.35.Ct

Comparison of strain relaxation in InGaAsN and InGaAs thin films

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.

Predicting GaAs surface shapes during MBE regrowth on patterned substrates

We have developed a coupled equations continuum model that explains the complex surface shapes observed in epitaxial regrowth on micron scale gratings. This model describes the dependence of the surface morphology on film thickness and growth temperature in terms of a few simple atomic scale processes including adatom diffusion, step-edge attachment and detachment, and a net downhill migration of surface adatoms. The continuum model reduces to the linear part of the Kardar-ParisiZhang equation with a flux dependent smoothing coefficient in the long wavelength limit.

Surface pattern evolution during thermal Cl2 etching of GaAs(001)

The evolution of one- and two-dimensional surface gratings during maskless thermal Cl2 etching of GaAs is investigated using atomic force microscopy. It is found that the limiting factor for pattern transfer is the anisotropy of the etch rate with respect to crystal orientation. A simple numerical model based on an interpolation of measured etch rates is presented that can be used to calculate the evolution of surface patterns.

Surfactant enhanced growth of GaNAs and InGaNAs using a Bi flux

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.