Abstract: A visible wavelength vertical cavity surface emitting laser suitable for single mode operation has an oxide aperture (81, 82) for concentrating electrical current within a central axial portion (143) of the device and a surface relief feature (144, 146) at an output surface of the device selecting for substantially single lateral mode of operation. The relationship between oxide confinement structure diameter (140) and surface relief feature diameter (141) has been mapped to provide optimum conditions for single mode behaviour and define a region of that space to produce optimum device performance in the visible device operating wavelength band between 630 nm and 690 nm.

Abstract: A light-emitting diode or laser diode comprises a sapphire substrate and, grown on the substrate, a GaN buffer layer, an n-doped GaN contact layer, an n-doped (AlGa)N cladding layer, a Zn-doped (InGa)N active layer, a p-doped (AlGa)N cladding layer and a p-doped GaN contact layer. Graded layers are introduced at the interfaces between the cladding layers and both the contact layers and the active layer. The constituency of each graded layer is graded from one side to the other of the layer such that the layer is lattice matched with the adjacent layer on each side with the result that the strain at the interfaces between the layers is reduced and the possibility of deleterious dislocations being introduced at the interfaces is minimised. By removing or reducing such dislocations, the efficiency of the operation of the device is increased.

Abstract: A method of growing a layer of Group III nitride material on a substrate by molecular beam epitaxy includes the steps of (i) disposing a substrate in a vacuum chamber, (ii) reducing the pressure in the vacuum chamber to a pressure suitable for epitaxial growth by molecular beam epitaxy, (iii) supplying ammonia through an outlet of a first supply conduit into the vacuum chamber so that the ammonia flows towards the substrate; and (iv) supplying a Group III element in elemental form through an outlet of a second supply conduit into the vacuum chamber so that said Group III element flows towards the substrate. The method causes a layer containing Group III nitride to be grown on the substrate by molecular beam epitaxy. In the method, the outlet of the first supply conduit is disposed nearer to the substrate than the outlet of the second supply conduit.

Abstract: A separate confinement heterostructure (SCH) laser device (LD) has: a quantum well active region within an optical guiding region; and, n-type and p-type cladding regions provided on opposite sides of the optical guiding region. An electron-capture layer is provided in the n-side portion of the optical guiding region. The composition of the electron-capture layer is set in such a manner that the minimum energy for X-electrons in the conduction band is lower than that in the surrounding parts of the active region and/or the n-side portion of the optical guiding region. The electron-capture layer is thick enough to bind X-electrons so that, in use, the electron-capture layer promotes the capture of the X-electrons. The electron-capture layer is disposed sufficiently close to the active region to permit transfer ot the captured X-electrons to at least one .GAMMA.-confined level in the active region.

Abstract: A light-emitting diode or laser diode comprises a sapphire substrate and, grown on the substrate, a GaN buffer layer, an n-doped GaN contact layer, an n-doped (AlGa)N cladding layer, a Zn-doped (InGa)N active layer, a p-doped (AlGa)N cladding layer and a p-doped GaN contact layer. Graded layers are introduced at the interfaces between the cladding layers and both the contact layers and the active layer. The constituency of each graded layer is graded from one side to the other of the layer such that the layer is lattice matched with the adjacent layer on each side with the result that the strain at the interfaces between the layers is reduced and the possibility of deleterious dislocations being introduced at the interfaces is minimized. By removing or reducing such dislocations, the efficiency of the operation of the device is increased.

Abstract: A method of forming a smooth, continuous compound semiconductor film, e.g., a GaN film, is provided. When a GaN film is formed in accordance with this method, Ga is caused to arrive at a sapphire substrate in accordance with a first arrival rate profile over a growth period during which the film is formed, and nitrogen is caused to arrive at the substrate in accordance with a second arrival rate profile over the growth period. The first and second arrival rate profiles are such that the Ga and N are caused to arrive simultaneoulsly at the substrate over the growth period and so that (i) during an initial part of the growth period, growth of the film takes place under a stoichiometric exccess of Ga and (ii) during a subsequent part of the growth period, growth of the film takes place under a stoichiometric excess of N.

Abstract: A separate confinement heterostructure laser device has an optical guiding region, an active region in the optical guiding region, and p-type and n-type cladding regions on opposite sides of the optical guiding region. At least one barrier layer is present within the p-type cladding region. The composition of the barrier layer is such that it has an X-minimum higher than that of adjacent parts of the p-type cladding region. The composition and/or thickness of the barrier layer is also such that it has a .GAMMA.-minimum which is higher than the X-minima of the adjacent parts of the p-type, cladding region. The thickness of the barrier layer is such as to prevent electron tunneling between the X-bands of the adjacent parts of the p-type cladding region on opposite sides of the barrier layer, and/or the compositions of the adjacent parts of the p-type cladding region on opposite sides of the barrier layer are sufficiently different from one another to prevent such tunneling.

Abstract: A semiconductor laser device includes an active region, a cladding region, and a carrier blocking layer of the same conductivity type as the cladding region disposed on tho same side of the active region as the cladding region. The carrier, blocking layer has a greater impurity concentration than the cladding region.

Abstract: A surface-emitting laser contains an optical cavity including a multiple quantum well (MQW) active region providing a source of optical emission in use. Top and bottom mirrors are disposed respectively above and below the MQW active region. The MQW active region is profiled so that it has a greater number of quantum wells in a central portion thereof than in a peripheral portion thereof. In alternative embodiments, a current-guiding region is profiled so that it has a first current-guiding portion with a relatively smaller aperture therethrough extending over a central portion of the MQW active region, and a second current-guiding portion with a relatively larger aperture therethrough; and one of the mirrors has a layer structure which, in a central portion of the cross-sectional area of such mirror, is different to that in a peripheral portion of said cross-sectional area.

Abstract: An optoelectronic semiconductor device is provided in which carrier transport towards the active region thereof is enhanced by the formation of a miniband within a superlattice region of the device having a repeating pattern of first and second semiconductor regions. The minimum energy level of the miniband is equal to or greater than the energy level of a guiding region between the active region and the superlattice region.

Abstract: A quantum confined device is provided having raised portions formed on opposing walls of a groove, thereby defining a region of reduced width in the vicinity of the intersection of the walls. During fabrication, a "V" groove is formed in a substrate and then further masking and etching steps are performed on the walls of the groove to form the raised portions. Quantum confined devices can be formed within the groove by epitaxial deposition of semiconducting layers into the region of reduced width.

Abstract: A quantum well structure is provided which is capable of efficiently confining electrons and holes in a quantum well layer. The quantum well structure includes a first cladding layer, a second cladding layer, and a plurality of quantum well layers and one or more barrier layers each disposed between the first cladding layer and the second cladding layer. The quantum well layers and the barrier layers are laminated in an alternating manner. The quantum well layers include at least two selected from the group consisting of a layer having tensile strain, a layer having no strain, and a layer having compressive strain. The thickness of each of the quantum well layers is selected so that the energy difference in each of the quantum well layers between the ground quantum state of an electron at the conduction band and the ground quantum state of a hole at the valence band is substantially the same.