E.G. Scott

Beryllium diffusion in GaInAs grown by molecular beam epitaxy

The diffusion of Be from buried Be‐doped layers in GaInAs has been studied for temperatures between 600 and 700 °C. An interstitial‐substitutional model is proposed for the diffusion mechanism, which is dependent on growth conditions and consistent with the data presented. Under growth conditions where Be transport is minimized GaInAs junction field‐effect transistors have been produced with transconductances in excess of 200 mS mm−1 for a 1‐μm gate length.

A photoluminescence study of Ga1-xInxAs/Al1-yInyAs quantum wells grown by MBE

Photoluminescence studies of Ga1-xInxAs/Al1-yInyAs quantum wells nominally lattice matched to InP are reported. The photoluminescence from two samples each having six quantum wells of thicknesses ranging from about 6 to 122 AA is studied in detail. The main emission peak associated with each quantum well is attributed to excitonic recombination. The emission from the 6 AA quantum well at 897.3 nm is found to have a peak width of only 18 meV at 4.2 K. Temperature dependence studies show that at 4.2 K the excitons are localised at potential fluctuations in the quantum wells. Impurity-related emission is also observed from some of the quantum wells.

Some comparisons of chemical beam epitaxy with gas source molecular beam epitaxy

Abstract This paper seeks to illustrate the major differences between chemical beam epitaxy (CBE) and gas source molecular beam epitaxy (GSMBE). The reasons for these differences nearly all eminate from the use of group III metal alkyls in CBE whereas GSMBE uses conventional elemental group III sources. From this difference can be traced the dissimilarity in growth mechanisms which can be further exemplified in some of the more important features of CBE. Using as an illustration the growth of GaAs from triethyl gallium, the model is extended to include the reduction in growth rate brought about by the addition of small quantities of In to the growing layer at temperatures in excess of 500°C. This is technologically important in the subsequent growth of InGaAs lattice matched to InP. The positive advantages of CBE, such as area uniformity and true selective area growth are also discussed in detail. InGaAs layers have been grown with a compositional uniformity of ±0.03% In and a thickness variation of

The growth of InP/InGaAs multi-quantum well modulator arrays by gas source MBE

Abstract InGaAs/InP multi-quantum well layers, suitable for use as quantum confined Stark effect modulators, have been grown by gas source MBE. Detailed analysis of interface perfection has been obtained by multiple crystal X-ray diffraction techniques and low temperature photoluminescence. Fabrication of a 4×4 modulator array is described, as is the potential for the fabrication of larger arrays. Growth of structures suitable for operation at lower applied voltages has been achieved with the use of coupled quantum wells. Even with the increased complexity of these structures, some containing 800 interfaces, low leakage devices have been demonstrated.

InGaAs/InP junction field-effect transistors with high transconductance made using metal organic vapor phase epitaxy

The growth and fabrication of a InGaAs/InP junction field-effect transistor using metal organic vapor phase epitaxy is reported for the first time. Very high extrinsic transconductance has been achieved (210 mS/mm for a gate length of 1.5 µm), by the use of a p-InP buffer layer which allows close to maximum electron velocity in the channel, and by using a self-alignment technique to give very low values of access resistance, typically 0.5 Ω.mm.

Electron microscope studies of interdiffusion in molecular beam epitaxy grown GaInAs/AlInAs multilayers

The thermal interdiffusion behavior of intrinsic nominally lattice‐matched GaInAs/AlInAs heterostructures grown by molecular‐beam epitaxy, studied using electron microscopy, is reported. At temperatures as low as 700 °C, significant degrees of interdiffusion are observed. X‐ray microanalysis of the multilayers reveals that the interdiffusion takes place along a nonlinear (that is, non‐lattice‐matched) path. This behavior has previously been attributed to the pronounced differences in the elemental diffusivities of the constituent binary compounds. In addition, high‐resolution electron microscopy (HREM) was used to determine the detailed interfacial structure of the material. Such a determination is only possible under favorable and well‐defined experimental conditions. The accuracy and limitations of HREM analysis of interfacial abruptness in semiconductor interfaces are commented on.

Characterisation of Ga1-xInxAs/Al1-yInyAs multiple quantum wells by Raman scattering

Two Ga1-xInxAs/Al1-yInyAs multiple quantum well structures are characterised using Raman spectroscopy. Raman scattering by zone folded longitudinal acoustic phonons is observed and analysed using the elastic continuum theory to determine the superlattice periods of the structures. The energies of the optical phonons in the ternary alloy layers have also been measured and their relationship to the alloy compositions is discussed.

Influence of buffer layer material on InGaAs FET optimisation

A study was performed to investigate whether the noise performance of delta-doped heterostructure-insulated-gate FETs (HIGFETs) is adequate for optical receiver applications. The suitability of gate insulator and buffer layers of both AlInAs and InP was investigated. The former has the wider bandgap and will thus give better confinement and lower gate leakage currents, whereas InP has the prospect of reduced trapping and thus of lower noise. The test structures and experimental procedures are described, and the results are discussed. It is found that the lower trap density of InP buffer layers does result in better noise performance if the bias conditions are chosen to minimize the effect of the poorer carrier confinement of InP.<<ETX>>

Parallel interconnection and neural network systems employing semiconductor array technology and computer-generated holography

An experimental 16-channel parallel interconnection system able to support 100 Mbits−1 per channel and an opto-electronic neural network operating at up to 50 Mbits−1 have been constructed to demonstrate the potential of optics in processing systems. Both experiments operate at a wavelength of 1.5μm. Components developed for these systems include arrays of InGaAs/InP MQW surface modulators for low-power electrical-to-optical conversion; InGaAs/InP for detector arrays, which are hybrid integrated with GaAs amplifier arrays; and computer-generated holograms for efficient beam splitting and to encode weights in the optical beam intensities. Each of these demonstrations has considerable scope for increasing the degree of parallelism and the operating speed. Recent modifications to the neural network enable the weights to be varied and training has been demonstrated with a novel algorithm that uses the high operating speed to advantage.

MBE growth of InP/InGaAs MQW modulators

Abstract Matched Stark effect MQW optical modulators in the InP/InGaAs materials system have been grown using double sided epitaxy (DSE) on both sides of a single InP wafer by gas source MBE. Coupled multi-quantum well stacks have been used to reduce the operating voltage of the devices (1.2 dB at -6 V unbiased), and group III cells incorporating conical crucibles have greatly improved the area uniformity (exciton absorption peak ±3 nm over 2 inches) making feasible the fabrication of modulators operating at the same wavelength over an entire wafer.