Abstract: A method of modifying the optical properties of a processed nitride semiconductor light-emitting device initially comprises disposing the processed nitride semiconductor light-emitting device in a vacuum chamber. One or more nitride semiconductor layers are then grown by molecular beam epitaxy thereby to modify the optical properties of the processed light-emitting device. Activated nitrogen, for example from a plasma source, is supplied to the vacuum chamber during growth of the nitride semiconductor layer(s). The use of activated nitrogen reduces the growth temperature required for the growth of the nitride semiconductor layer(s), as the need for thermal activation of a nitrogen species is eliminated. Moreover, use of a growth method such as, for example, plasma-assisted MBE to grow the nitride semiconductor layer(s) allows much more precise control of their thickness and composition.

Abstract: A semiconductor device comprises an active region (4), a cladding layer (5,7), and a saturable absorbing layer (6) disposed within the cladding layer. The saturable absorbing layer comprises at least one portion (11a) that is absorbing for light emitted by the active region and comprises at least portion (11b) that is not absorbing for light emitted by the active region. The fabrication method of the invention enables the non-absorbing portion(s) (11b) of the saturable absorbing layer (6) to produced after the device structure has been fabricated. This allows the degree of overlap between the non-absorbing portion(s) (11b) of the saturable absorbing layer (6) and the optical mode of the laser to be altered after the device has been grown.

Abstract: A method of fabricating the active region of a semiconductor light-emitting device, in which the active region comprises a plurality of barrier layers (11,13,15,17) with each pair of barrier layers being separated by a quantum well layer (12,14,16), comprises annealing each barrier layer (11,13,15,17) separately. Each barrier layer (11,13,15,17) is annealed once it has been grown, and before a layer is grown over the barrier layer. A device grown by the method of the invention has a significantly higher optical power output than a device made by a convention fabrication process having a single annealing step.

Abstract: A semiconductor device comprises an active region (4), a cladding layer (5,7), and a saturable absorbing layer (6) disposed within the cladding layer. The saturable absorbing layer comprises at least one portion (11a) that is absorbing for light emitted by the active region and comprises at least portion (11b) that is not absorbing for light emitted by the active region. The fabrication method of the invention enables the non-absorbing portion(s) (11b) of the saturable absorbing layer (6) to produced after the device structure has been fabricated. This allows the degree of overlap between the non-absorbing portion(s) (11b) of the saturable absorbing layer (6) and the optical mode of the laser to be altered after the device has been grown.

Abstract: A method of manufacturing a nitride semiconductor device comprises the steps of: growing an InxGa1-xN (0?x?1) layer, and growing an aluminium-containing nitride semiconductor layer over the InxGa1-xN layer at a growth temperature of at least 500° C. so as to form an electron gas region at an interface between the InxGa1-xN layer and the nitride semiconductor layer. The nitride semiconductor layer is then annealed at a temperature of at least 800° C. The method of the invention can provide an electron gas having a sheet carrier density of 6×1013 cm?2 or greater. An electron gas with such a high sheet carrier concentration can be obtained with an aluminium-containing nitride semiconductor layer having a relatively low aluminium concentration, such as an aluminium mole fraction of 0.3 or below, and without the need to dope the aluminium-containing nitride semiconductor layer or the InxGa1-xN layer.

Abstract: A method of growing an AlGaN semiconductor layer structure by Molecular Beam Epitaxy comprises supplying ammonia, gallium and aluminium to a growth chamber thereby to grow a first (Al,Ga)N layer by MBE over a substrate disposed in the growth chamber. The first (Al,Ga)N layer has a non-zero aluminium mole fraction. Ammonia is supplied at a beam equivalent pressure of at least 1 10?4 mbar, gallium is supplied at a beam equivalent pressure of at least 1 10?8 mbar and aluminium is supplied at a beam equivalent pressure of at least 1 10?8 mbar during the growth step. Once the first (Al,Ga)N layer has been grown, varying the supply rate of gallium and/or aluminium enables a second (Al,Ga)N layer, having a different aluminium mole fraction from the first (Al,Ga)N layer to be grown by MBE over the first (Al,Ga)N layer. This process may be repeated to grown an (Al,Ga)N multilayer structure.

Abstract: The invention provides a method of growing an (In, Ga)N multiplayer structure by molecular beam epitaxy. Each GaN or InGaN layer in the multilayer structure is grown at a substrate temperature of at least 650° C., and this provides improved material quality. Ammonia gas is used as the source of nitrogen for the growth process. Ammonia and gallium are supplied to the growth chamber at substantially constant rates, and the supply rate of indium to the growth chamber is varied to select the desired composition for the layer being grown. This allows the structure to be grown at a substantially constant growth rate. The substrate temperature is preferably kept constant during the growth process, to avoid the need to interrupt the growth process to vary the substrate temperature between the growth of one layer and the growth of another layer.

Abstract: A method of MBE growth of a semiconductor layer structure comprises growing a first (Al,Ga)N layer (step 13) over a substrate at the first substrate temperature (T1) using ammonia as the nitrogen precursor. The substrate is then cooled (step 14) to a second-substrate temperature (T2) which is lower than the first substrate temperature. An (In,Ga)N quantum well structure is then grown (step 15) over the first (Al,Ga)N layer by MBE using ammonia as the nitrogen precursor. The supply of ammonia to the substrate is maintained continuously during the first growth step, the cooling step, and the second growth step. After completion of the growth of the (In,Ga)N quantum well structure, the substrate may be heated to a third temperature (T3) which is greater than the second substrate temperature (T2). A second (Al,Ga)N layer is then grown over the (In,Ga)N quantum well structure (step 17).

Abstract: A method of growing a p-type nitride semiconductor material by molecular beam epitaxy (MBE) uses bis(cyclopentadienyl)magnesium (Cp2Mg) as the source of magnesium dopant atoms. Ammonia gas is used as the nitrogen precursor for the MBE growth process. To grow p-type GaN, for example, by the method of the invention, gallium, ammonia and Cp2Mg are supplied to an MBE growth chamber; to grow p-type AlGaN, aluminium is additionally supplied to the growth chamber. The growth process of the invention produces a p-type carrier concentration, as measured by room temperature Hall effect measurements, of up to 2 1017 cm-3, without the need for any post-growth step of activating the dopant atoms.

Abstract: A semiconductor light-emitting device and a method of manufacture thereof A method of manufacturing a semiconductor light-emitting device comprises selectively etching a semiconductor layer structure (16) fabricated in a nitride materials system and including an aluminium-containing cladding region or an aluminium-containing optical guiding region (5). The etching step forms a mesa (17), and also exposes one or more portions of the aluminium-containing cladding region or the aluminium-containing optical guiding region (5). The or each exposed portion of the aluminium-containing cladding region or the aluminium-containing optical guiding region (5) Is then oxidised to form a current blocking layer (18) laterally adjacent to and extending laterally from the mesa. When an electrically conductive contact layer (11) is deposited, the current blocking layer (18) will prevent the contact layer (11) from making direct contact with the buffer layer (3).

Abstract: A method of manufacturing a semiconductor light-emitting device is provided. The method includes the step of depositing an electrically conductive material on one or more selected portions of the surface of a semiconductor wafer including a substrate and a layer structure, the layer structure having at least a first semiconductor layer of a first conductivity type and a second semiconductor conductivity layer of a second conductivity type different from the first conductivity type, the first layer being between the second layer and the substrate, such that the electrically conductive material forms a contact to the first semiconductor layer. The method further includes the step of dicing the wafer to form a plurality of light-emitting devices, each light-emitting device having a respective part of the electrically conductive material.

Abstract: A method of fabricating the active region of a semiconductor light-emitting device, in which the active region comprises a plurality of barrier layers (11,13,15,17) with each pair of barrier layers being separated by a quantum well layer (12,14,16), comprises annealing each barrier layer (11,13,15,17) separately. Each barrier layer (11,13,15,17) is annealed once it has been grown, and before a layer is grown over the barrier layer. A device grown by the method of the invention has a significantly higher optical power output than a device made by a convention fabrication process having a single annealing step.

Abstract: A method of fabricating a continuous wave semiconductor laser diode in the (Al,Ga,In)N materials system comprises: growing, in sequence, a first cladding region (4), a first optical guiding region (5), an active region (6), a second optical guiding region (7) and a second cladding region (8). Each of the first cladding region (4), the first optical guiding region (5), the active region (6), the second optical guiding region (7) and the second cladding region (8) is deposited by molecular beam epitaxy.

Abstract: A semiconductor light-emitting device fabricated in a nitride material system has an active region (5) disposed over a substrate (1). The active region (5) comprises a first aluminium-containing layer (12) forming the lowermost layer of the active region, a second aluminium-containing layer (14) forming the uppermost layer of the active region, and at least one InGaN quantum well layer (13) disposed between the first aluminium-containing layer (12) and the second aluminum-containing layer (14). The aluminium-containing layers (12,14) provide improved carrier confinement in the active region (5), and so increase the output optical power of the device. The invention may be applied to a light-emitting diode (11) or to a laser diode.

Abstract: A semiconductor laser device (15) comprises a substrate (16). A first mirror structure (17), an active region (18) and a second mirror structure (19) are disposed in this order over the substrate (16). The second mirror structure has a first portion (28) having a first width (W1) and a second portion (29) having a second width (W2) less than the first width (W1). The first portion (28) of the second mirror structure (19) is disposed between the second portion (29) of the second mirror structure (19) and the active region (18). An etching stop layer (23) is provided between the first portion (28) of the second mirror structure (19) and the second portion (29) of the second mirror structure (19). A contact (24) is disposed on the surface of the first portion of the second mirror structure, where it is not covered by the second portion of the second mirror structure.

Abstract: A semiconductor device comprises an active region (4), a cladding layer (5,7), and a saturable absorbing layer (6) disposed within the cladding layer. The saturable absorbing layer comprises at least one portion (11a) that is absorbing for light emitted by the active region and comprises at least portion (11b) that is not absorbing for light emitted by the active region.

Abstract: A method of growing a p-type nitride semiconductor material having magnesium as a p-type dopant by molecular beam epitaxy (MBE), comprises supplying ammonia gas, gallium and magnesium to an MBE growth chamber containing a substrate so as to grow a p-type nitride semiconductor material over the substrate. Magnesium is supplied to the growth chamber at a beam equivalent pressure of at least 1 10-9 mbar, and preferably in the range from 1 10-9 mbar to 1 10-7 mbar during the growth process. This provides p-type GaN that has a high concentration of free charge carriers and eliminates the need to activate the magnesium dopant atoms by annealing or irradiating the material.

Abstract: This invention relates to a method of growing a nitride semiconductor layer by molecular beam epitaxy comprising the steps of: a) heating a GaN substrate (S) disposed in a growth chamber (10) to a substrate temperature of at least 850° C.; and b) growing a nitride semiconductor layer on the GaN substrate by molecular beam epitaxy at a substrate temperature of at least 850° C., ammonia gas being supplied to the growth chamber (10) during the growth of the nitride semiconductor layer; wherein the method comprises the further step of commencing the supply ammonia gas to the growth chamber during step (a), before the substrate temperature has reached 800° C.

Abstract: The invention provides a method of growing an (In,Ga)N multilayer structure by molecular beam epitaxy. Each GaN or InGaN layer in the multilayer structure is grown at a substrate temperature of at least 650° C., and this provides improved material quality. Ammonia gas is used as the source of nitrogen for the growth process.

Abstract: A method of growing a nitride semiconductor layer, such as a GaN layer, by molecular beam epitaxy comprises the step of growing a GaAlN nucleation layer on a substrate by molecular beam epitaxy. The nucleation layer is annealed, and a nitride semiconductor layer is then grown over the nucleation layer by molecular beam epitaxy. The nitride semiconductor layer is grown at a V/III molar ratio of 100 or greater, and this enables a high substrate temperature to be used so that a good quality semiconductor layer is obtained. Ammonia gas is supplied during the growth process, to provide the nitrogen required for the MBE growth process.