International Standard Electric Corporation

Nortel Networks Corporation

Stc, Inc

Standard Telephones & Cables Limited

Peter D Greene

Gillies D Pitt

Stephen E Turley

Edward John Thrush

Alfred Rodney Adams

Daniel S Renner

Mark Silver

David H Whysall

The or each strained quantum well layer of a quantum confined Stark effect modulator is provided with a substructure of substructure layers not all having the same lattice constant. The thickness and composition of these substructure layers may be arranged to produce a differential strain that is asymmetric with respect to the mid-plane of the quantum well and so skews the hole wavefunctions for heavy-holes, HH,, and light-holes, LH,, in opposite directions. This enables the choice of composition designed to provide substantial matching of the E,-HH,and E,-LH,Stark shifts for one particular polarity of applied field, thereby providing a modulation facility that is substantially polarisation insensitive. Alternatively, the thickness and composition of the layers may be chosen to produce a symmetrical strain profile in which the same effect is provided, but for both polarities of applied field.

Polarization-insensitive optical modulators

A quantum confined Stark effect (QCSE) optical modulator element has one or more quantum wells each bounded by assymetric barriers. This provides a device in which the direction and magnitude of the electric field induced absorption edge shift corresponds to the polarity and intensity of an applied electric field.

Optical modulator with superlattice having asymmetric barriers

A mass transport process for use in the manufacture of semiconductor devices, particularly but not exclusively low threshold semiconductor lasers in the InP/InGaAsP system, involves the arrangement of a cover wafer (18) of the material to be grown adjacent to a semiconductor wafer (15) on which the material is to be grown, their disposition together with a crystalline alkali halide (20) in a crucible (16), and heating the crucible, which is almost but not completely sealed, in a hydrogen stream. For the manufacture of InP/InGaAsP lasers and the growth of InP, the alkali halide may comprise KI, RbI or CsI and a controlled amount of In metal (21) may be optionally contained in the crucible (16) to control the balance between growth of InP for defining the laser active region and erosion of InP from other areas of the wafer. Growth is achieved at temperatures comparable with liquid phase epitaxy processing temperatures.

Mass transport of indium phosphide

A method of making a channel substrate buried heterostructure InP/(In,Ga)(As,P) laser avoids the need to use two separate stages of epitaxial growth by using a channel in a (100) surface substrate 1 extending in the [011] direction with {111}B sides. This allows the channel to be made before the growth of an (In,Ga)(As,P) blocking layer 3 which can be grown under conditions which do not require the use of a mask to prevent nucleation on the channel sides. The same technique is also applicable to the manufacture of a terraced substrate laser incorporating a blocking layer.

Injection laser manufacture

A Hall effect device comprises a thin substrate free epitaxially grown semiconductor body mounted in a magnetically permeable, e.g. ferrite, housing. The layer, which is preferably gallium arsenide or gallium indium arsenide, is grown on a substrate which, after device processing is complete, is removed by a selective etching process. In view of the relatively high sensitivity and good noise characteristics such a device with its flux concentrator is small, since the flux concentrators are themselves much smaller than with conventional Hall effect systems. Other semiconductor materials from which the novel thin Hall effect devices can be made include silicon.

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Harlow, United Kingdom

Peter D Greene