B. R. Semyagin

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.

Experimental determination of the incorporation factor of As4 during molecular beam epitaxy of GaAs

Abstract The incorporation factor of arsenic during molecular beam epitaxy of GaAs using As 4 and Ga was experimentally determined. It was found that the incorporation factor of As 4 significantly exceeded the value 0.5 for a wide spectrum of growth conditions. In several cases it is close to unity. The relative sensitivity coefficient, η of the Bayard–Alpert ion gauge was defined for arsenic in the form of As 4 and As 2 .

Local stresses induced by nanoscale As–Sb clusters in GaAs matrix

Microstructure of GaAs films grown by molecular-beam epitaxy at low temperature and delta doped with Sb was studied by transmission electron microscopy. The material contained 0.5 at. % excess of arsenic that precipitated during post growth anneals. The Sb δ doping was found to strongly affect the microstructure of precipitates (clusters) and their ripening rate upon annealing. Segregation of Sb impurity in the clusters was revealed. In contrast to the well known pure As clusters, the As–Sb clusters induced strong local deformations in the surrounding GaAs matrix. Until a threshold diameter of 7–8 nm the clusters and surrounding matrix were coherently strained. Larger clusters were associated with dislocation loops of interstitial type. The cluster-loop orientation relationships were determined. Relaxation of local strains by formation of the dislocation loops was studied both experimentally and theoretically.

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.

Enhanced As–Sb intermixing of GaSb monolayer superlattices in low-temperature grown GaAs

As–Sb compositional intermixing was studied by transmission electron microscopy (TEM) in GaAs films grown by molecular-beam epitaxy at low temperature (LT) and δ doped with antimony. The TEM technique was calibrated by imaging the as-grown films with δ layers containing various amounts of Sb. The calibration allowed us to deduce the effective As–Sb interdiffusion coefficient from apparent thickness of the Sb δ layers in the films subjected to isochronal anneals at 400–600 °C. The As–Sb intermixing in LT GaAs was found to be much enhanced when compared to conventional material. Its temperature dependence yields a diffusion coefficient of DAs–Sb=2×10−14 exp(−0.62±0.15 eV/kt) cm2 s−1. Since the kick-out mechanism operating under equilibrium conditions is valid for As–Sb interdiffusion in GaAs, the enhanced intermixing was attributed to an oversaturation of arsenic self-interstitials in the LT GaAs films. The effective activation energy for As–Sb interdiffusion in LT GaAs seems to be reasonably close to the m...

In–Ga intermixing in low-temperature grown GaAs delta doped with In

Low-temperature grown GaAs films with indium delta layers are studied by transmission electron microscopy. The delta layers in the as-grown film are found to be as thick as four monolayers (ML) independently of a nominal In deposit of 0.5 or 1 ML, a thickness which reflects the film surface roughness during the low-temperature growth. A pronounced In–Ga intermixing is observed in the films subjected to 500–700 °C isochronal anneals. The In–Ga interdiffusion diffusivity is evaluated. The effective activation energy for In–Ga interdiffusion is found to be 1.1±0.3 eV which is significantly smaller than a value of 1.93 eV for a stoichiometric GaAs. The difference seems to result from a loss of the gallium vacancy supersaturation upon annealing, and is consistent with an annihilation enthalpy of 0.8 eV.

Enhanced precipitation of excess As on antimony delta layers in low-temperature-grown GaAs

Delta doping with antimony isovalent impurity has been employed as a precursor for two-dimensional precipitation of excess arsenic in GaAs grown by molecular-beam epitaxy at low substrate temperature (LT-GaAs), and subsequently annealed. LT-GaAs films delta doped with indium isovalent impurity showed previously to provide two-dimensional As cluster sheets were studied for comparison. Small clusters observed by transmission electron microscopy at the Sb delta layers had an unusual lens shape and, probably, nonrhombohedral microstructure. These clusters induced strong local strains in the surrounding GaAs matrix. After annealing under the same conditions, the clusters at the Sb delta layers were found to be bigger than those at the In delta layers. Additionally, nucleation of the arsenic clusters at the Sb delta layers occurs at a relatively low annealing temperature. The observed precipitation features indicate that delta doping with Sb is more effective for two-dimensional precipitation of the excess As i...

Enhanced arsenic excess in low-temperature grown GaAs due to indium doping

We have found that isovalent indium doping enhances arsenic excess in GaAs films grown by molecular beam epitaxy at low temperature. An increase in lattice expansion and near infrared optical absorption, as well as higher density of As clusters, have been observed in the indium-doped films when compared to the conventional indium-free ones.

High-power, efficient, semiconductor saturable absorber mode-locked Yb:KGW bulk laser.

A high-power, diode-pumped, semiconductor saturable absorber mode-locked Yb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8 W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at a pulse repetition frequency of 62 MHz. For Np polarization, 143 fs pulses with pulse energy of 139 nJ and average output power of up to 8.6 W with optical-to-optical efficiency of 31% were generated.

Measurements of parameters of the low-temperature molecular-beam epitaxy of GaAs

Phase diagrams of GaAs (001) surface structures were used to calibrate sensors of the substrate temperature and As flux in molecular-beam epitaxy systems. The sublimation temperature of amorphous layers of As adsorbed on GaAs was measured. It was shown that this temperature is constant and does not depend on the rate of substrate heating, layer thickness, or the degree of vacuum in the system. The sublimation temperature of amorphous As can be used as a reference point to calibrate the substrate temperature in the range of low growth temperatures.