C.R. Stanley

A UNIVERSAL DAMAGE INDUCED TECHNIQUE FOR QUANTUM WELL INTERMIXING

We report a novel technique for quantum well intermixing which is simple, reliable and low cost, and appears universally applicable to a wide range of material systems. The technique involves the deposition of a thin layer of sputtered SiO2 and a subsequent high temperature anneal. The deposition process appears to generate point defects at the sample surface, leading to an enhanced intermixing rate and a commensurate reduction in the required anneal temperature. Using appropriate masking it is possible to completely suppress the intermixing process, enabling large differential band gap shifts (over 100 meV) to be obtained across a single wafer.

Waveguide microcavity based on photonic microstructures

A waveguide based microcavity exhibiting a quality factor Q/spl ap/2500 has been realized by incorporating a /spl lambda//4 phase shift into a 1-D photonic microstructure. The microstructure has an overall length of 3 /spl mu/m, consists of a deeply etched grating with very narrow (75 nm) air-gaps and exhibits a third-order stop band in the 800-900 nm wavelength regime. A comparison between measurement and simulation suggests that there is a thin (approximately 18 nm) skin of oxidized material at the etched semiconductor-air interfaces.

Design and construction of an optoelectronic crossbar switch containing a terabit per second free-space optical interconnect

The completed detailed design and initial phases of construction of an optoelectronic crossbar demonstrator are presented. The experimental system uses hybrid very large scale integrated optoelectronics technology whereby InGaAs-based detectors and modulators are flip-chip bonded onto silicon integrated circuits. The system aims to demonstrate a 1-Tb/s aggregate data input/output to a single chip by means of free-space optics.

FRANZ-KELDYSH EFFECT IN AN OPTICAL WAVEGUIDE CONTAINING A RESONANT TUNNELING DIODE

Optical modulation in a waveguide containing a resonant tunneling diode has been observed. The observations are in agreement with a model which assumes that the modulation effect is due to a Franz–Keldysh band‐edge shift produced by the electric field developed over a depletion region association with operation of the resonant tunneling diode. The effect has device potential for optical modulation at microwave frequencies.

Modification of the second-order optical nonlinearities in AlGaAs asymmetric multiple quantum well waveguides by quantum well intermixing

We demonstrate that a quantum well intermixing technique can be used to control the second-order nonlinearity χzzz(2) in an AlGaAs asymmetric coupled quantum well waveguide structure at 1.52 μm. Photoluminescence measurements also indicate that the spatial resolution of the impurity-free vacancy disordering process used for quantum well intermixing is better than 1.5 μm which should be sufficient for first-order quasiphase-matched second harmonic generation.

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.

Improvements in strain‐balanced InGaAs/GaAs optical modulators for 1047‐nm operation

We demonstrate a self‐electro‐optic effect device (SEED) designed to work at 1047 nm to match the high power available from a Nd:YLF laser. The device uses a strain‐balanced InGaAs/GaAs multiple quantum well grown on a GaAs substrate with an InGaAs buffer layer of linearly graded composition. It has improved performance compared to previous devices in this system. We have obtained a single pass modulation contrast ratio of 1.74 by applying 13‐V reverse bias, and have found 99% photodetection quantum efficiency under the built‐in junction field. Bistability in a resistor‐SEED configuration is demonstrated.

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.

An investigation of CH4/H2 reactive ion etching damage to thin heavily doped GaAs metal–semiconductor field effect transistor layers during gate recessing

Damage during the reactive ion etching in CH4/H2 of thin, heavily silicon doped, molecular beam epitaxy grown GaAs layers has been investigated. Hall effect and CV measurements showed near complete loss of the free carrier concentration on etching due to passivation by hydrogen of the silicon donor activity. Annealing for a few minutes at 400u2009°C was sufficient to recover the sheet concentration of the material, measured by Hall effect, but only to a limit determined by the dc bias employed during etching. At 800 V only 5% of the carriers were restored, while reducing the dc bias to 80 V allowed 70% to 80% recovery. CV measurements showed that increased surface depletion accounted for the loss of sheet concentration, while the doping profile in the undepleted channel was unaffected. At 80 V dc bias, the increased surface depletion was only 2.6 nm. Additionally Hall mobility was restored by annealing, to close to the original value of the unetched material, indicating minimal reactive ion etching damage to ...