S. Hasenöhrl

Resistivity anisotropy in ordered InxGa1−xP grown at 640 °C

The anisotropy of electrical properties in ordered InxGa1−xP epitaxial layers was studied. These samples were prepared by a low-pressure metalorganic chemical vapor phase epitaxy technique at the growth temperature of 640 °C. Resistivity measurements using a four-point-probe method have shown that samples with a low misfit value (0–1.5×10−3) are electrically uniform. For samples with higher misfit the anisotropy of resistivity markedly increases up to a maximum of 950. Comparing the results obtained from x-ray diffraction, low temperature photoluminescence, and atomic force microscopy experiments, we have shown that lattice mismatch can support the evolution and extension of the ordering effect in the InxGa1−xP layers.

Anisotropic surface structure in ordered strained InGaP

We have studied the surface structure of ordered In x Ga 1-x P organometallic vapour phase epitaxy (OMVPE)-grown layers using optical microscopy, atomic force microscopy (AFM), and synchrotron topography. The layers were intentionally lattice mismatched (0.388 ≤ x ln < 0.552), and they exhibited a surface structure with three basic features. The first one is a fine island structure with the size of surface features in the range of 10 nm, which is very similar for all layers regardless of their misfit. This fine structure is superposed to surface undulations with lateral dimensions in the micrometer scale. The surface structure of the strained layers (tensile and compressed) follows the dislocation line pattern revealed by synchrotron topography. The change of the dominant misfit dislocation direction from [011] to [0 - 11] is observed for the layer still under tension with Δa/a = - 3.28 x 10 3 . The best surface morphology and no misfit dislocations are observed for the slightly compressed layer with Δa/a = + 9.42 x 10 4. With increased compression in the layers, we observed at first the creation of large (probably metal) precipitates and then the formation of a misfit dislocation net. The third feature observed on the surface of ordered layers is the presence of hillocks. Their density, shape and orientation depend on lattice mismatch.

Approaching the pT range with a 2DEG InGaAs/InP Hall sensor at 77 K

Abstract The noise of two-dimensional electron gas InGaAs/InP Hall sensors of various dimensions was studied. In the first part of the work we show that for large-scale sensors (>0.2 mm linear dimension) at 77 K and at 1 kHz, a sensitivity better then 1 nT can be achieved. The second part of present work deals with the noise measurements of 2 and 10 μm sensors dependent on bias current, frequency, applied magnetic field and temperature. It was found that the low-frequency noise of the 10 μm sensor rapidly increased for applied magnetic field, but the noise of the 2 μm sensor is a complicated function of temperature and magnetic field: for low temperatures and fields 1–3 T is the low-frequency noise of the sensor suppressed.

OMCVD growth of InP and InGaAs on InP non-planar substrates patterned with {110} quasi facets

Non-planar low-pressure organometallic chemical vapour deposition (LP OMCVD) of InP and InGaAs was performedon patterned(1 0 0) semi-insulating InP substrates. The patterns were 15- mm-high long mesa ridges bounded by (1 1 0) and ð1 % Þ quasi facets and(1 0 0) top surfaces. Growth rates andsurface morphologies on the facets were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical microscopy. Both InP andInGaAs nucleatedsufficiently on the facets. While InP layers were smooth, InGaAs nucleatedthrough facetted trapezoidal islands. The mechanism of facetting is qualitatively discussed. The InGaAs facetting as well as accompanying roughness were partly suppressedat lower growth temperatures. r 2001 Elsevier Science B.V. All rights reserved.

Crystallographic dependence of OMVPE InGaAs/InP lateral growth on patterned (100) InP substrates prepared by wet etching

Abstract InP layers and InP/InGaAs structures were grown at 600°C using OMVPE on non-planar wet-etch InP substrates with patterns aligned at various angles Θ within [010] and [01-1] as well as [001] and [0-11]. The patterns were 15-μm-high ordinary mesa-shaped ridges with the sidewall facet angle α dependent on the alignment angle Θ. Within 0.5°

SEM and AFM characterisation of high-mesa patterned InP substrates prepared by wet etching

Abstract The aim of this study has been to optimise a reliable technological process that would be capable of producing quality mesa etches (40 μm high) into (100) SI InP substrates yielding well-defined smooth (211) faceted walls and (100) bottom etched planes. Such well-defined patterned substrates can serve for non-planar overgrowth experiments with the aim to create 2DEGs at tilted heterostructures and finally to design and manufacture novel magnetic-field sensors. Using xHCl:1H3PO4 solutions well-defined smooth (211)A surfaces were produced for 0.5

InGaP/GaAs/InGaP quantum wires grown on pre-patterned substrates by MOVPE

Abstract We prepared InGaP/GaAs/InGaP V-groove heterostructures incorporating quantum wires using metalorganic chemical vapour deposition technique. Influence of the growth temperature on the facetting and growth rate according to the crystallographic orientation was studied. Low temperature photoluminescence was used for characterisation of quantum structures prepared. To enhance a photoluminescence signal from quantum wire, the two step Au evaporation was used with the aim to suppress PL signals from the sidewalls.

Polar diagram of wet-etched [100] InP

A modified wagon-wheel-mask technique was used to determine data for the reconstruction of a polar diagram of InP crystal wet etched in etchants based on HCl and H/sub 3/PO/sub 4/. It is demonstrated that the facet revelation and mask underetching within /spl plusmn/5/spl deg/ around [001] are very sensitive to the etchant composition as well as to mask orientation.

Sulphur doping of GaSb grown by atmospheric pressure MOVPE

Abstract Sulphur-doped GaSb epitaxial layers are grown on GaSb and GaAs substrates by atmospheric pressure MOVPE. Trimethylgallium and trimethylantimony are used as the Ga and Sb sources, respectively. Hydrogen sulphide (1% H2S diluted in hydrogen) is employed as the sulphur source. The mole fraction of H 2 S in the reactor ranging from 6.1 × 10 −6 to 1.2×10 −4 results in the hole concentrations from 2.8×10 17 to 2.5×10 18 cm −3 , respectively. Low temperature ( T = 5 K) photoluminescence measurements show a sulphur-related transition S 1 near 732 meV indicating that sulphur is successfully incorporated into GaSb. The PL spectra of the samples grown with a H 2 S mole fraction larger than 6.2 × 10 −5 consist only of a native acceptor transition A and a sulphur-related transition S 1 The position of S 1 transition is independent of the H 2 S mole fraction. The ratio of the intensity of the sulphur-related transition S 1 to the that of the transition A increases from 0 up to 1.5 with increasing H 2 S mole fraction.

Photoluminescence characterization of InGaP/GaAs/InGaP quantum wires

We investigated the photoluminescence of InGaP/GaAs/InGaP heterostructures with the aim to prepare quantum wires by the epitaxial overgrowth of V-groove patterned substrates. Planar and V-groove patterned GaAs semiinsulating substrates were used for epitaxial growth in a low-pressure MOVPE equipment with a horizontal reactor. Low temperature photoluminescence measurements show that the composition of the InGaP ternary compound prepared on the patterned substrates is shifted to a higher InP mole fraction compared with the planar ones. On the other hand, the measurement on the V-grooved samples showed that the PL peak is shifted to higher energies (i.e. to the higher amount of Ga), which indicates a change in the ternary composition of about 5%. Crystalline quality of the overgrown structures was studied by transmission electron microscopy. Both, photoluminescence and photoluminescence polarization measurement show that quantum wires can be successfully prepared in the InGaP/GaAs/InGaP system.