A. Kaluza

Modeling and experimental verification of deposition behavior during AlGaAs growth: a comparison for the carrier gases N2 and H2

Abstract A modeling and experimental study is carried out to understand why low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) of AlGaAs in nitrogen atmosphere differs from that in hydrogen in a horizontal tube type of reactor. To this end flow, heat transfer as well as the key chemical species’ mass transport are considered. The increased uniformity in N 2 atmosphere is related to the higher molecular weight and, therefore to the higher gas density of the carrier resulting in a flow structure that is more favorable for improved growth rate uniformity of AlGaAs on the substrate. Due to the so called “cold finger” [L. Stock, W. Richter, J. Crystal Growth 77 (1986) 144; D.F. Fotiadis, M. Boekholt, K.F. Jensen, W. Richter, J. Crystal Growth 100 (1990) 577.] effect as well as the enhanced inertia of the carrier gas and lower diffusion coefficients of the growth rate limiting chemical species in N 2 , lower total flow rates are found to be optimal for material quality and layer thickness uniformity when using N 2 as carrier gas. The dependence of growth rate uniformity on the carrier gas and total flow rate can only be understood by the detailed numerical modeling of three-dimensional flow, heat and species’ mass transfer with resulting layer deposition on the susceptor. The results of experiments are in good agreement with the modeling computations.

Real-time calibration of wafer temperature, growth rate and composition by optical in-situ techniques during AlxGa1−xAs growth in MOVPE

In this paper we report a novel technique, based on optical measurements, to measure the true temperature of the wafer surface during epitaxial growth. It will be shown that this temperature can deviate considerably from the susceptor temperature measured with thermocouples or pyrometers. For this purpose we employed combined in-situ reflectance anisotropy spectroscopy and spectroscopic reflectance measurements in a number of different metal-organic vapor phase epitaxy (MOVPE) reactors. Measurements have been performed on rotating and non-rotating samples during growth of GaAs, AlAs and AlxGa1� xAs. We demonstrate that in a single growth run the reading of a conventional thermocouple can be calibrated to the true wafer temperature, the growth rate can be determined and process calibration for the AlGaAs composition can be established. r 2002 Elsevier Science B.V. All rights reserved.

Josephson effect in Nb/two-dimensional electron gas structures using a pseudomorphic InxGa1−xAs/InP heterostructure

Superconducting Nb–In0.53Ga0.47As/In0.77Ga0.23As/InP–Nb contacts with an electrode separation of 450 nm were fabricated. Due to the high mobility of the two-dimensional electron gas, the current transport can be described within the clean limit regime. At 0.3 K a critical current of 3.8 μA was obtained for 6 μm wide contacts leading to a characteristic voltage of 190 μV. The decrease of the critical current with increasing temperature can be explained by a theory developed by A. Chrestin, T. Matsuyama, and U. Merkt [Phys. Rev. B 49, 498 (1994)], which takes δ-shaped barriers at the superconductor/semiconductor interfaces into account.

Magnetic and structural properties of GaN thin layers implanted with Mn, Cr, or V ions

We report on magnetic and structural properties of n- and p-type GaN layers implanted with Mn, Cr, and V. The samples were subsequently annealed in a N2 atmosphere at a constant temperature in the range between 700 and 1050°C. Measurements of the magnetization as a function of magnetic field as well as of the temperature show typical paramagnetic behavior. In addition, a weak antiferromagnetic coupling between the implanted ions was observed. 3d-metal rich precipitates of crystalline nature are revealed by high resolution transmission electron microscopy.

Electron transport in modulation-doped GaAs v-groove quantum wires

Abstract We report the growth of modulation-doped GaAs/Al x Ga 1− x As v-groove quantum wires and structural, electrical and optical investigations of their electronic states and transport properties. By using alternative group III precursors on partially SiO 2 masked pre-patterned GaAs substrates, samples have been fabricated which permit electrical measurements of single isolated wire structures without the need for additional electron-beam lithography. Magneto-transport was measured as a function of tilt angle of the incident magnetic field to identify the formation of low-dimensional electron gases in different parts of the structure. Photoluminescence investigations reveal 1D and 2D confined states which show different carrier heating when electric fields are applied along the wire structure.

On the choice of precursors for the MOVPE-growth of high-quality Al0.30Ga0.70As/GaAs v-groove quantum wires with large subband spacing

Abstract MOVPE growth is used to prepare high-quality v-groove quantum wires in the AlGaAs/GaAs system. The particular aim of this work is to find suitable precursor combinations and growth conditions with which quantum wire structures can be achieved, where only the lowest subband is occupied and on which truly one-dimensional transport can be studied. Different precursor combinations of triethylgallium (TEGa), trimethylgallium (TMGa), trimethylaluminium (TMAl) and dimethylethylaminenalane (DMEAAl) were employed for growth of the Al0.30Ga0.70As barrier layer. Calculations of the 2D-Schrodinger-equation show, that suitable quantum wire geometries are obtained when using combinations with TMGa. High-quality material is achieved at 575°C for TMGa/DMEAAl and 595°C for TMGa/TMAl. In general, lower growth temperatures lead to the preferential lower radii of curvature for a given precursor combination. A comparison of the best two combinations shows that TMGa/TMAl is best suited for growth of the Al0.30Ga0.70As barrier layer with respect to the intended application.

Adjustment of the critical current in a Nb–InxGa1−xAs/InP Josephson contact by light exposure

The critical current of a Nb–InGaAs/InP Josephson junction is increased stepwise by light exposure. Shubnikov–de Haas effect measurements under illumination show that the increase of the critical current originates from photogenerated electrons in the quantum well. A further enhancement of the critical current is gained under continuous illumination.

Fermi-edge singularities in the photoluminescence spectrum of modulation-doped GaAs v-groove quantum wires

Abstract We report the observation of strong Fermi-edge singularities in the photoluminescence spectrum of strongly-confined, modulation-doped GaAs v-groove quantum wires. The behaviour of the singularity has been investigated at high excitation intensity, and both lattice and electrical heating. The latter produces a strong reduction of the singularity due to Fermi surface smearing, whereas, increased photoexcitation produces complex electron–hole correlation effects.

Fermi-edge singularities in the photoluminescence and magneto-optical spectra of modulation-doped v-groove quantum wires

Abstract We report the obervation of a strong Fermi-edge singularity in the photoluminescence spectrum of a degenerate one-dimensional electron system in modulation-doped GaAs/GaAlAs v-groove quantum wires. The singularity is pronounced due to 1D subband mixing, which is further enhanced by an applied transverse magnetic field.