C. P. Hains

Very low threshold current density room temperature continuous-wave lasing from a single-layer InAs quantum-dot laser

Continuous-wave (CW) lasing operation with a very low threshold current density (J/sub th/=32.5 A/cm/sup 2/) has been achieved at room temperature by a ridge waveguide quantum-dot (QD) laser containing a single InAs QD layer embedded within a strained InGaAs quantum well (dot-in-well, or DWELL structure). Lasing proceeds via the QD ground state with an emission wavelength of 1.25 /spl mu/m when the cavity length is longer than 4.2 mm. For a 5-mm long QD laser, CW lasing has been achieved at temperatures as high as 40/spl deg/C, with a characteristic temperature T/sub 0/ of 41 K near room temperature. Lasers with a 20 /spl mu/m stripe width have a differential slope efficiency of 32% and peak output power of >10 mW per facet (uncoated).

Effect of strain-compensation in stacked 1.3μm InAs∕GaAs quantum dot active regions grown by metalorganic chemical vapor deposition

We have introduced tensile layers embedded in a GaAs matrix to compensate compressive strain in stacked 1.3μm InAs quantum dot (QD) active regions. The effects of the strain compensation are systematically investigated in five-stack and ten-stack QD structures where we have inserted InxGa1−xP (x=0.30 or 0.36) layers. High-resolution x-ray diffraction spectra quantify the overall strain in each sample and indicate >35% strain reduction can be accomplished. Both atomic force and transmission electron microscope images confirm that strain compensation improves material crystallinity and QD uniformity. With aggressive strain compensation, room temperature QD photoluminescence intensity is significantly increased demonstrating a reduced defect density.

Effect of dislocation density on thermal boundary conductance across GaSb/GaAs interfaces

We report on the thermal boundary conductance across structurally-variant GaSb/GaAs interfaces characterized by different dislocations densities, as well as variably-rough Al/GaSb interfaces. The GaSb/GaAs structures are epitaxially grown using both interfacial misfit (IMF) and non-IMF techniques. We measure the thermal boundary conductance from 100 to 450 K with time-domain thermoreflectance. The thermal boundary conductance across the GaSb/GaAs interfaces decreases with increasing strain dislocation density. We develop a model for interfacial transport at structurally-variant interfaces in which phonon propagation and scattering parallels photon attenuation. We find that this model describes the measured thermal boundary conductances well.

Quantum dot lasers based on a stacked and strain-compensated active region grown by metal-organic chemical vapor deposition

We demonstrate an InAs∕GaAs quantum dot (QD) laser based on a strain-compensated, three-stack active region. Each layer of the stacked QD active region contains a thin GaP (Δao=−3.8%) tensile layer embedded in a GaAs matrix to partially compensate the compressive strain of the InAs (Δao=7%) QD layer. The optimized GaP thickness is ∼4MLs and results in a 36% reduction of compressive strain in our device structure. Atomic force microscope images, room-temperature photoluminescence, and x-ray diffraction confirm that strain compensation improves both structural and optical device properties. Room-temperature ground state lasing at λ=1.249μm, Jth=550A∕cm2 has been demonstrated.

Cascadable, latching photonic switch with high optical gain by the monolithic integration of a vertical-cavity surface-emitting laser and a pn-pn photothyristor

The authors report the first demonstration of a cascadable, photonic switch based on the monolithic integration of a multi-quantum-well vertical-cavity surface-emitting laser (VCSEL) and a latching pn-pn photothyristor grown by low-pressure metalorganic vapor-phase epitaxy (LP-MOCVD). The VCSEL and pn-pn photothyristor structures can be independently optimized for optical switching, logic, and memory functions. Optical switching with high gain (30000), high contrast (30 dB), low switching power (11 nW), and latching memory have been demonstrated. The integrated pn-pn/VCSEL switch not only represents a volatile optical memory, but also can be used to implement a new class of optical logic gates with latching logic outputs.<<ETX>>

Selective area growth of InAs quantum dots formed on a patterned GaAs substrate

We describe the growth and characterization of InAs quantum dots (QDs) on a patterned GaAs substrate using metalorganic chemical vapor deposition. The QDs nucleate on the (001) plane atop GaAs truncated pyramids formed by a thin patterned SiO2 mask. The base diameter of the resulting QDs varies from 30 to 40nm depending on the size of the mask. With specific growth conditions, we are able to form highly crystalline surface QDs that emit at 1.6μm under room-temperature photopumped conditions. The crystalline uniformity and residual strain is quantified in high-resolution transmission electron microscopy images and high-resolution x-ray reciprocal space mapping. These strained QDs may serve as a template for selective nucleation of a stacked QD active region.

Organometallic vapor phase epitaxy growth and optical characteristics of almost 1.2 μm GaInNAs three-quantum-well laser diodes

We report organometallic vapor-phase epitaxy (OMVPE) growth and optical characteristics of 1.17–1.20 μm double-heterostructure laser diodes with three Ga0.7In0.3N0.003As0.997 (7 nm)/GaAs(10 nm) quantum wells (GaInNAs/GaAs QWs). Three GaInNAs/GaAs QWs were successfully grown by OMVPE using dimethylhydrazine as the N precursor. Strong room-temperature photoluminescence at the 1.17–1.19 μm regime with a full width at half maximum of 33 meV has been routinely achieved. By using three GaInNAs/GaAs QWs as the gain medium of the GaInNAs laser, room temperature operation with a threshold current density of 1.2 kA/cm2 has been successfully demonstrated.

Monolithic wavelength-graded VCSEL and resonance-enhanced photodetector arrays for parallel optical interconnects

Monolithic arrays of wavelength-graded vertical-cavity surface-emitting lasers (VCSELs) and resonance-enhanced photodetectors (PDs) have been realized with the same epilayer structure using the topography-controlled enhancement and reduction of the metal-organic chemical vapor deposition (MOCVD) growth rate on a patterned substrate. The repeatability of this technique was demonstrated by using different VCSEL and resonance-enhanced photodetector (REPD) arrays from the same wafer.

Ground-state lasing of stacked InAs∕GaAs quantum dots with GaP strain-compensation layers grown by metal organic chemical vapor deposition

We report the device characteristics of stacked InAs∕GaAs quantum dots (QDs) with GaP strain-compensation (SC) layers grown by metal organic chemical vapor deposition. By inserting GaP SC layers within the stacked structures, decrease in the density of QDs by stacking QDs can be suppressed due to reduction of overall compressive strain within the stacked QDs. We demonstrate ground-state lasing at 1.265μm of six layers of InAs∕GaAs QDs with GaP SC layers. The threshold current density is as low as 108A∕cm2. We also assess the internal loss and maximum modal gain of fabricated QD lasers by using a segmented contact method. The internal loss is as low as 5cm−1, and the maximum modal gain of the ground state of the stacked QDs is approximately 10cm−1.

Inverting and latching optical logic gates based on the integration of vertical-cavity surface-emitting lasers and photothyristors

Inverting optical logic gates based on the monolithic integration of a vertical-cavity surface-emitting laser (VCSEL) with a heterojunction photothyristor (PNPN) are described. Logic functions INVERT, NAND, and NOR are experimentally demonstrated for the first time using latchable and cascadable PNPN/VCSEL switches, which can be triggered with very low optical energy, while producing high optical gain and optical contrast. These gates are integrable on a single epitaxial structure to provide multifunctional logic and memory arrays.<<ETX>>