A.H. Kean

Measurement of aluminum concentration in epitaxial layers of AlxGa1−xAs on GaAs by double axis x‐ray diffractometry

The composition of a series of AlxGa1−xAs layers grown epitaxially by molecular beam epitaxy (MBE) on GaAs has been measured independently by double axis x‐ray diffractometry and reflection high‐energy electron diffraction. From a quadratic fit to the data, we deduce the lattice parameter mismatch between AlAs and GaAs and the Poisson ratio of AlAs. Asymmetric reflection rocking curves and synchrotron x‐ray topography have been used to show that the anomalously low substrate‐layer peak splitting for the 1‐μm‐thick AlAs layer results from relaxation, which is asymmetric. Use of the AlAs rocking curve peak splitting corrected for relaxation yields a mismatch of 1600 ppm (±1%) between AlAs and GaAs, and 0.28±0.01 for the Poisson ratio of AlAs.

Size dependence of the thermal broadening of the exciton linewidth in GaAs/Ga0.7Al0.3As single quantum wells

We have studied the temperature dependence of the linewidth, Γ(T), of the fundamental absorption edge in bulk GaAs and four GaAs/Ga0.7Al0.3As single quantum wells of different well width using photoreflectance. As a result of the size dependence of the exciton‐longitudinal optical phonon interaction, the thermal broadening of the linewidth diminishes as the dimensionality and size of the system are reduced.

Electrical characterization of molecular beam epitaxial GaAs with peak electron mobilities up to ≊4×105 cm2 V−1 s−1

The effect of varying the temperature (T cr) of an As4→As2 cracker furnace between 600 and 700 °C on the properties of GaAs grown by molecular beam epitaxy has been evaluated using 4–300 K Hall measurements and 4.2 K far‐infrared photoconduction spectroscopy, in an extension of earlier work on high‐mobility material (Ref. 1). The residual donors are silicon and sulphur with mid‐1013 cm−3 concentrations under As2‐growth conditions (T cr=700 °C). By lowering T cr, the silicon concentration is reduced substantially, leaving sulphur as the principal impurity. A 15‐μm‐thick layer grown with T cr=650 °C has measured free‐electron densities of ≊2.8×1013 cm−3 and peak mobilities ≊4×105 cm2 V−1 s−1 at ≊28–42 K, the highest ever recorded in bulk GaAs.

4 × 105 cm2 V−1 s−1 peak electron mobilities in GaAs grown by solid source MBE with As2

Abstract A detailed study into the molecular beam epitaxy of high purity n-GaAs with arsenic dimers has been undertaken, culminating in the growth of a layer with a peak mobility of ≈4.0 × 10 5 cm 2 V −1 s −1 at 28–40 K, the highest ever recorded in bulk GaAs.

Gallium desorption from (Al,Ga)As grown by molecular beam epitaxy at high temperatures

Abstract We report on a detailed study by cross-sectional transmission electron microscopy (XTEM) of gallium desorption from (Al,Ga)As structures grown by molecular beam epitaxy (MBE) at substrate temperatures in the range 680–730°C. The Ga desorption rate ( D r ) depends only on substrate temperature, with an activation energy, E a for re-evaporation of 2.56 eV, comparable to E a for Ga evaporation from liquid gallium. The presence of aluminum has no measurable influence on D r except where the desorbing gallium flux exceeds the incident flux ( D r a G r ), when a few monolayers of residual GaAs can be detected on an AlAs surface. No As 4 overpressure dependence has been observed. In practice, therefore, multilayer structures of (Al,Ga)As with controlled thicknesses and compositions can be grown with As 4 in the temperature regime investigated by making a constant allowance for D r , irrespective of the compositional fraction of the (Al,Ga)As.

Silicon compensation and scattering mechanisms in two-dimensional electron gases on (110)GaAs

Abstract A study of the MBE growth of (001) and (110) (Al,Ga)As is reported, and the efficiency of Si as an n-type dopant in (110)GaAs is accessed. A 40 nm spacer two-dimensional electron gas (2DEG) structure grown on (110)GaAs gives a mobility of 540,000 cm 2 V −1 s −1 at 4 K after illumination. The dominant scattering mechanisms in 2DEGs on (110) and (001)GaAs grown under the separate optimum growth conditions for the two orientations are compared.

Peak electron mobilities between 2.75 and 3.32×105 cm2 V−1 s−1 in GaAs grown by molecular beam epitaxy with As2

Exceptionally pure n‐GaAs has been grown without intentional doping by solid‐source molecular beam epitaxy (MBE) using arsenic dimers (As2). Peak electron mobilities in the range 2.75–3.32×105 cm2 V−1 s−1 at temperatures of ≊40–50 K with free‐electron densities n=1×1014 cm−3 have been measured for a series of layers grown under a variety of conditions. These mobilities are among the highest recorded for MBE‐grown GaAs.

250 Å spacer GaAs-AlGaAs two-dimensional electron gas (2DEG) structures with mobilities in excess of 3 × 106 cm2 V-1 s-1 at 4 K

The mobility of a 250 A spacer 2DEG structure has been improved by optimizing a number of MBE growth conditions. The effects of impurities from the Si dopant cell, the GaAs-AlGaAs interface growth temperature, the aluminium source and machine preconditioning have been examined. Under optimum growth conditions 4 K mobilities >3.0×10 6 cm 2 V -1 s -1 are achieved consistently

Growth of (Al,Ga)As structures on (110)-GaAs by MBE

Abstract The growth of (Al,Ga)As structures on both (110)-GaAs and the (110)-GaAs surface exposed by in-situ cleaving of a (100)-GaAs substrate has been investigated. “T-junctions” of GaAs layers have been grown in two growth steps where there is no discernible interface (as observed by high resolution SEM) between the two layers. High intensity photoluminescence has been observed from quantum wells grown on (110)-GaAs wafers at 480°C. The efficiency of p-type doping by beryllium has been measured by the Hall effect. No differences between the doping levels and mobilities at both ambient temperature and 77 K have been measured for (110) and (100) surfaces.

Raman Scattering and Photoluminescence of GaAs-Based Nanostructures

Recent developments in Electron Beam Lithography (EBL) and Reactive Ion Etching (RIE), among other semiconductor fabrication techniques, have enabled semiconductor material to be patterned into arrays of quantum well wires (QWW) and quantum dots (OD). The regime of 1- and 0-D quantization is achieved by reducing the dimensions of the semiconductor to lengths comparable to the de Broglie wavelength. Optical spectroscopic evidence of 1-D quantization has been reported by the group at A T & T Bell Laboratories1, at Stuttgart University2 and at the NTT laboratories in Japan3. 0-D quantization has been harder to confirm in optical spectroscopy. So far, significant work has taken place in assessing the interaction of photons with QD with particular emphasis placed on radiative recombination mechanisms4.