V. V. Preobrazhenskii

Free-standing and overgrown InGaAs/GaAs nanotubes, nanohelices and their arrays

Abstract The possibility is shown to fabricate a wide class of free-standing nano-objects based on few monolayers thick scrolled heterostructures. Using an ultra-thin film (1 ML GaAs:1 ML InAs), nanotubes with an inside diameter of ≈2 nm have been obtained, which constitutes the limiting size for this system. Molecular-beam-expitaxy overgrown structures with nanotubes embedded into GaAs have been obtained.

A technique for fabricating InGaAs/GaAs nanotubes of precisely controlled lengths

Single-crystal nanotubes of controlled lengths were produced on sidewalls of V-grooves and on a cleaved facet of a heterostructure. This was done using selective molecular-beam-epitaxy growth of a strained InGaAs/GaAs strip and subsequent self-rolling of this strip in a tube. The proposed technique is capable of ensuring good reproducibility for all sizes and exact positioning of nanotubes.

Two-dimensional precipitation of As clusters due to indium delta-doping of GaAs films grown by molecular beam epitaxy at low temperature

We have shown that two-dimensional layers of arsenic nanoclusters separated by a cluster-free GaAs matrix can be formed using indium delta-doping of GaAs films grown by molecular beam epitaxy at low temperature . Spatially ordered structures of As clusters have been obtained in epitaxial LT GaAs films doped with Si donors and Be acceptors and also in undoped films.

High-resolution x-ray diffraction study of InAs-GaAs superlattices grown by molecular-beam epitaxy at low temperature

InAs-GaAs superlattices grown by molecular-beam epitaxy at low temperature are investigated by high-resolution x-ray diffractometry. It is shown that despite a very high density of point defects due to the presence of excess arsenic, the as-grown superlattice has high crystal perfection. An analysis of the changes in the x-ray diffraction curves shows that high-temperature annealing, which is accompanied by the formation of As clusters and diffusion of indium, produces significant structural transformations in the GaAs matrix and at the interfaces.

A valved cracking phosphorus beam source using InP thermal decomposition and its application to MBE growth

The principal design of a newly developed two-zone valved cracking phosphorus P2 molecular beam source with greatly improved performance based on InP thermal decomposition is outlined. Precise dimer phosphorus beam flux control is accomplished due to a thoughtfully designed and externally activated faucet placed between the InP decomposition zone and the cracking area of P4 vapors. Experimental tests show that the source can be easily incorporated into the standard ion-pumped molecular beam epitaxy (MBE) machine and can be used successfully for the MBE growth of device quality III–V single and multi-component phosphide epilayers incorporated into single- and multi-layer heterostructures with sharp interfaces.

Indium layers in low-temperature gallium arsenide: Structure and how it changes under annealing in the temperature range 500–700 °C

Transmission electron microscopy is used to study the microstructure of indium δ layers in GaAs(001) grown by molecular beam epitaxy at low temperature (200 °C). This material, referred to as LT-GaAs, contains a high concentration (≈1020 cm−3) of point defects. It is established that when the material is δ-doped with indium to levels equivalent to 0.5 or 1 monolayer (ML), the roughness of the growth surface leads to the formation of InAs islands with characteristic lateral dimensions <10 nm, which are distributed primarily within four adjacent atomic layers, i.e., the thickness of the indium-containing layer is 1.12 nm. Subsequent annealing, even at relatively low temperatures, leads to significant broadening of the indium-containing layers due to the interdiffusion of In and Ga, which is enhanced by the presence of a high concentration of point defects, particularly VGa, in LT-GaAs. By measuring the thickness of indium-containing layers annealed at various temperatures, the interdiffusion coefficient is determined to be DIn-Ga=5.1×10−12 exp(−1.08 eV/kT) cm2/s, which is more than an order of magnitude larger than DIn-Ga for stoichiometric GaAs at 700 °C.

Free-Standing InAs/InGaAs Microtubes and Microspirals on InAs (100)

A new material system for creating InAs-based free-standing micro- and nanoobjects is proposed. For the first time, InAs/InGaAs microtubes and microspirals were obtained, including tubes containing two-dimensional electron gas, ordered arrays of tubes, and tubes protruding over the substrate edge. First measurements of the electrical conductivity of InAs/InGaAs microtubes were performed.

Interface corrugation in GaAs/AlAs (311)A superlattices

GaAs/AlAs (311)A superlattices are studied by cross-sectional high-resolution transmission electron microscopy X-HRTEM. An anisotropic relief on GaAs/AlAs (311)A interfaces with a height up to 6 ML is observed, predominantly aligned along the [233] direction. A strong (up to 12 ML) highly anisotropic modulation of the thickness of the GaAs layers is found, which can explain the in-plane anisotropy of carrier transport previously observed in this system. At the same time, the thickness of the AlAs layers appeared to be nearly constant. The X-HRTEM studies have revealed no 32 A periodicity of the GaAs/AlAs (311)A interfacial structure, although a distinct (8×1) surface reconstruction of both GaAs and AlAs surfaces was observed by reflection high-energy electron diffraction during growth.

Structure and properties of InGaAs layers grown by low-temperature molecular-beam epitaxy

This paper describes studies of InGaAs layers grown by molecular-beam epitaxy on InP (100) substrates at temperatures of 150–480 °C using various arsenic fluxes. It was found that lowering the epitaxy temperature leads to changes in the growth surface, trapping of excess arsenic, and an increased lattice parameter of the epitaxial layer. When these lowtemperature (LT) grown samples are annealed, the lattice parameter relaxes and excess arsenic clusters form in the InGaAs matrix. For samples grown at 150 °C and annealed at 500 °C, the concentration of these clusters was ∼8×1016 cm−3, with an average cluster size of ∼5 nm. Assuming that all the excess arsenic is initially trapped in the form of antisite defects, the magnitude of the LT-grown InGaAs lattice parameter relaxation caused by annealing implies an excess arsenic concentration (NAs−NGa−NIn)/(NAs+NGa+NIn)=0.4 at.%. For layers of InGaAs grown at 150 °C, a high concentration of free electrons (∼1×1017 cm−3) is characteristic. Annealing such layers at 500 °C decreases the concentration of electrons to ∼1×1017 cm−3. The results obtained here indicate that this change in the free-electron concentration correlates qualitatively with the change in excess arsenic concentration in the layers.

Arsenic cluster superlattice in gallium arsenide grown by low-temperature molecular-beam epitaxy

Molecular-beam epitaxy at 200 °C is used to grow an InAs/GaAs superlattice containing 30 InAs delta-layers with a nominal thickness of 1 monolayer, separated by GaAs layers of thickness 30 nm. It is found that the excess arsenic concentration in such a superlattice is 0.9×1020 cm−3. Annealing the samples at 500 and 600 °C for 15 min leads to precipitation of the excess arsenic mainly into the InAs delta-layers. As a result, a superlattice of two-dimensional sheets of nanoscale arsenic clusters, which coincides with the superlattice of the InAs delta-layers in the GaAs matrix, is obtained.