T.S. Yeoh

Epitaxy of InAs quantum dots on self-organized two-dimensional InAs islands by atmospheric pressure metalorganic chemical vapor deposition

Fully coherent InAs quantum dots and InAs quantum dots grown on self-organized two-dimensional (2D) islands by atmospheric pressure metalorganic chemical vapor deposition are investigated. The significantly lower critical thickness window of between 1 and 2.0 monolayers for fully coherent dots is attributed to the suppression of a segregated indium floating layer. An InAs quantum dot density of 4.7×1010 cm−2 was achieved on GaAs, and a highly localized InAs quantum dot density of over 5×1012 cm−2 was achieved on 2D InAs islands.

Selective growth of InAs quantum dots by metalorganic chemical vapor deposition

We report results of both strain-driven surface segregation of indium from InGaAs thin films as well as selective area epitaxy of InAs quantum dots using these films. InAs segregation from an underlying InGaAs film allows for preferential growth of quantum dots when additional InAs is deposited. By using standard lithography techniques, a two-step selective growth process for quantum dots is achieved. Furthermore, by utilizing self-assembled nanostructures as a template, selective growth of coalesced wires and dots with 100-nm feature sizes are realized.

Dual-wavelength InGaAs-GaAs ridge waveguide distributed Bragg reflector lasers with tunable mode separation

The design and operation of integrated dual-wavelength sources are reported. These InGaAs-GaAs ridge waveguide (RW) distributed Bragg reflector (DBR) lasers consist of a common gain section and two, separate DBR sections. Multiple current injection is not necessary for these lasers to operate in dual-wavelength. Dual-wavelength operation is easily achieved by simply biasing the gain section. A relatively low coupling coefficient /spl kappa/ in the front grating reduces the added cavity loss for the back grating mode. Therefore, the back grating mode reaches threshold easily. Also, the addition of a spacing section lowers the current induced thermal interaction between the two uniform grating sections, significantly reducing the inadvertent wavelength drift. As a result, biasing the front DBR section results in tunable mode pair separations (/spl Delta//spl lambda/) as small as 0.3 nm and as large as 6.9 nm.

Dual-wavelength asymmetric cladding InGaAs-GaAs ridge waveguide distributed Bragg reflector lasers

The design and operation of dual-wavelength InGaAs-GaAs asymmetric cladding ridge waveguide distributed Bragg reflector (DBR) lasers are reported. DBR lasers with mode pair separations of 4.1, 8.4, and 16.9 nm exhibit stable, simultaneous, dual-wavelength operation in current ranges of 40-52 mA, 32-42 mA, and 28-35 mA, respectively. Within the stated current ranges, all lasing modes exhibit at least 20-dB sidemode suppression, and approximately 30-dB sidemode suppression under optimum operating conditions.

Curved waveguides for spatial mode filters in semiconductor lasers

Curved waveguides are used as a lateral spatial mode filter to increase the threshold for the first-order mode in high-power narrow stripe semiconductor lasers. Beam propagation analysis is used to determine optimal waveguide geometries and radii of curvature to establish appropriate amounts of bend loss. Curved waveguide devices are fabricated and compared against conventional devices. Use of a curved waveguide increases the current level at which lateral beam instabilities occur from /spl sim/400 to /spl sim/700 mA with no decline in slope efficiency.

900-mW high brightness buried ridge lasers by selective area epitaxy

A study has been made of high power single lateral mode buried ridge lasers fabricated by selective area epitaxy. Several ridge thicknesses have been evaluated simultaneously in a single fabrication run. These lasers operate purely in the fundamental mode to output powers in excess of 450 mW, after which they are subject to beam steering or higher order mode operation. For weakly guided lasers, the output remains in a narrow lobe [full-width at half-maximum (FWHM)] = 4/spl deg/-6/spl deg/, stable at a given current value, up to output powers of 900 mW in CW tests.

The role of the InGaAs surface in selective area epitaxy of quantum dots by indium segregation

The surface of strained InGaAs films for selective regrowth of InAs nanostructures is investigated by atomic force microscopy and Rutherford backscattering. 3.3-nm-thick In0.33Ga0.67As films were annealed at temperatures between 400 and 800 °C. Significant indium desorption was found to occur at temperatures above 550 °C. The optimum parameters are presented for selective growth of InAs quantum dots having densities of 6.6×1010 cm−2 on In0.33Ga0.67As films.

Novel design for high-power single-lateral-mode lasers

A new laser design for single-mode high-power applications is reported. The waveguide is a laterally flaring and transversely tapering GaAs buried ridge fabricated by selective area epitaxy. Single-lateral-mode powers of 200 mW were achieved.

650-mW single lateral mode power from tapered and flared buried ridge laser

Very high single lateral mode output powers of 650 mW are obtained from a diode laser with a unique waveguide design. The waveguide flares in the lateral dimension to create a larger spot size on the facet and simultaneously tapers in the transverse dimension to inhibit propagation of higher order lateral modes. These GaAs buried ridge devices are fabricated by selective area epitaxy.

InAs quantum dot selective area epitaxy using InGaAs thin films

A novel method of quantum dot selective area epitaxy of InAs quantum dots using an InGaAs pattern is presented. Indium segregation from an underlying InGaAs layer allows for preferential growth of InAs quantum dots on InGaAs when additional material is deposited. By using standard lithography techniques, selective area epitaxy was achieved on 20% InGaAs layers with a dot density of 3/spl times/10/sup 10/ cm/sup -2/ without the need for subsequent regrowth steps. The selective area quantum dot epitaxy was also observed to occur on self-organized 100 nm InAs 2D mesas with a high local selective area quantum dot density of 3.1/spl times/10/sup 12/ cm/sup -/2.