R. D. Heller

Visible spectrum (645 nm) transverse electric field laser operation of InP quantum dots coupled to tensile strained In0.46Ga0.54P quantum wells

Data are presented that demonstrate the continuous wave room-temperature transverse-electric field (TE) visible-spectrum (645 nm) heterostructure laser operation of single-layer compressively strained 3.75 monolayer equivalent InP quantum dots (QDs) coupled to 60 A wide tensile-strained In0.46Ga0.54P quantum wells (QWs). The simple stripe geometry (200 μm×4 μm) InP QD+InGaP QW heterostructure laser is capable of high performance despite the coupling of two competing recombination systems. The InP QD+InGaP QW laser exhibits low threshold (∼31 mA), high quantum efficiency (72%, ∼1.38 mW/mA), a relatively high characteristic temperature T0 of 69 K, and a shift in wavelength at temperature of 0.19 nm/°C.

Visible spectrum (654 nm) room temperature continuous wave InP quantum dot coupled to InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructure laser

Data are presented demonstrating the cw 300 K visible spectrum (654 nm) laser operation of a single 7.5 monolayer InP quantum dot (QD) layer coupled by a 20 A In0.5Al0.3Ga0.2P barrier to an auxiliary 70 A In0.5Ga0.5P quantum well (QW) that, via resonant tunneling, assists carrier collection, thermalization, and lateral rearrangement in the QDs. The simple stripe-geometry (530 μm×10 μm) InP QD+InGaP QW heterostructure laser, enhanced by the QW and operating on an upper QD state (42% quantum efficiency), is capable of over 10 mW/facet cw 300 K operation in spite of the weak heat sinking of probe operation.

Er-doped AlGaAs native oxides: photoluminescence characterization and process optimization

We present 300 K photoluminescence (PL) characterization data for wet thermal native oxides of Al/sub 0.58/Ga/sub 0.42/As films grown by metal organic chemical vapor deposition and doped with Er via multiple high-energy ion implants (for 0.0675, 0.135, and 0.27 atomic percent (at.%) peak Er concentrations), and Al/sub 0.5/Ga/sub 0.5/As and Al/sub 0.8/In/sub 0.2/As films doped with Er (0.03-0.26 at.%) during molecular beam epitaxy crystal growth. Broad spectra with a /spl sim/50-nm full-width at half-maximum and a PL peak at 1.534 /spl mu/m are observed, characteristic of Al/sub 2/O/sub 3/:Er films. The dependencies of PL intensity, spectra, and lifetime on annealing temperature (675/spl deg/C-900/spl deg/C), time (2-60 min) and As overpressure (0-0.82 atm) are studied to optimize the annealing process, with As considered as a possible quenching mechanism. Wet and dry-oxidized films are compared to explore the role of hydroxyl (OH) groups identified by Fourier transform infrared (FTIR) spectroscopy. FTIR experiments employing heavy water (D/sub 2/O) suggest that OH groups in wet oxidized AlGaAs come mainly from post-oxidation adsorption of atmospheric moisture. AlGaAs:Er films wet oxidized with 0.1% O/sub 2/ added to the N/sub 2/ carrier gas show a fourfold PL intensity increase, doubled PL lifetime to /spl tau//spl sim/5.0 ms (0.27 at.% implanted sample), and the lowest degree of concentration quenching.

Effect of Si delta doping on the luminescence properties of InP/InAlP quantum dots

We show that the cathodoluminescence (CL) properties of InP quantum dots (QDs) grown on In0.5Al0.5P matrix layers, lattice-matched to (001) GaAs substrates, can be greatly improved by introducing silicon delta doping in the layer adjacent to the QDs. Under optimized conditions, the room-temperature CL intensity of QDs can be improved by ∼16 times. We speculate that the increased CL intensity is caused by the efficient capture of electrons from the reservoir of the delta-doped layer into the QDs, which, to some extent, counterbalances the thermal escape of electrons from the QDs. A temperature-dependent CL study of InP QDs grown without Si delta doping shows a quenching of the CL at high temperatures, which supports the unipolar escape of electrons from QDs, while delta-doped QDs show an anomalous behavior. The QD integrated CL intensity increases with temperature and then decreases after 200 K. This anomalous behavior is interpreted as caused by competition between two processes: (1) thermal activation of...

Effect of the InAlGaP matrix on the growth of self-assembled InP quantum dots by metalorganic chemical vapor deposition

InP self-assembled quantum dots (QDs) were deposited on lattice-matched In0.5(AlxGa1−x)0.5P matrices grown on (001) GaAs substrates by using metalorganic chemical vapor deposition. We found that the Al concentration in the matrix has a great influence on the size of the InP QDs. For a fixed volume of deposited InP, the size of the QDs decreases with an increase in the Al concentration in the In0.5(AlxGa1−x)0.5P matrix. We suggest that this variation in QD size is a result of an alloying effect caused by atomic intermixing between the InP dots and the underlying matrix material. The stronger intermixing between InP and the Ga-rich matrices (relative to Al-rich matrices) results in larger QDs on these surfaces. The intermixing effect, as expected, reduces the lattice mismatch and, as a result, leads to a larger critical thickness of the wetting layer when the growth temperature is higher. The growth of InP QDs on an InAlP matrix with a thin GaP intermediate buffer layer also supports the interpretation as a...

Growth of InP quantum dots on vicinal GaAs (100) substrates by metalorganic chemical vapor deposition

We report the growth of InP self-assembled quantum dots (QDs) on In0.5Al0.5P and In0.5(Al0.6Ga0.4)0.5P matrices, lattice matched on 0°, 2°, 6°, and 25° off-axis (100) GaAs substrates by metalorganic chemical vapor deposition. The influence of the substrate misorientation on the morphology and cathodoluminescence (CL) properties of the InP QDs was investigated. We find that the density of QDs grown on both In0.5Al0.5P and In0.5(Al0.6Ga0.4)0.5P matrices increases with the misorientation angle up to 6° off (100). At the same time, the dispersion of the QD size is getting larger for the growth on an In0.5Al0.5P matrix, but not for the growth on an In0.5(Al0.6Ga0.4)0.5P matrix. The InP QDs grown on In0.5(Al0.6Ga0.4)0.5P on 25° off-axis substrates are two-dimensionally well ordered. Moreover, the ordering improves and the density of QDs increases with an increase in the deposition of InP. The room-temperature CL intensity of InP QDs grown on a 25° off In0.5(Al0.6Ga0.4)0.5P is much stronger than that for InP QDs...

Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.

Tunneling injection quantum dot lasers

We investigate tunneling injection quantum-dot (QD) lasers both theoretically and experimentally. Our laser structure consists of two tensile-strained quantum wells (QWs) coupled to a compressive-strained QD layer. The QWs serve as efficient carrier collectors and as a medium to inject electrons into the QDs by tunelling. Polarization-resolved amplified spontaneous emission (ASE) spectroscopy is used to extract the transverse-electric (TE) and transverse-magnetic (TM) polarized optical gain spectra at very low to near threshold injection currents. At a low bias current, the TE polarized ASE from the ground state of the QD layer is observed. At an intermediate current level, the coupling of the QW ground state to the QD excited state becomes important and an increase of the TM polarized emission from the tensile-strained QWs at a higher energy level becomes significant. Near threshold current, we observe TE gain narrowing due to the QD excited-state activation and the pinning of TM gain with subsequent TE lasing above threshold. We explain the physics of tunneling injection from the QWs into the QDs and how the tunneling injection affects the polarization resolved optical gain spectra as the injection current level increases.

Gain narrowing and output behavior of InP-InGaAlP tunneling injection quantum-dot-well laser

Polarization-resolved amplified spontaneous emission (ASE) and gain from tensile-strained multiple quantum wells (QWs) coupled to a single layer of compressively strained quantum dots (QDs) show interesting output characteristics. Low current injection reveals transverse electric polarized ASE from the QD ground state and QD-coupled-QW state. Additionally, transverse magnetic ASE from the QW state is observed. The modal gain of this laser shows coupled active state activation which is evident by spectral narrowing and change from QW-like to QD-like spectrum.

Experimental demonstration of the polarization-dependent photon-mediated carrier redistribution in tunneling injection InP quantum-dot lasers with external-grating feedback

Measured modal gain spectra of the tunneling injection InP quantum-dot (QD) laser with and without an external feedback are presented to experimentally demonstrate the polarization-dependent photon-mediated carrier redistribution in the tunneling injection QD laser. The peak gain wavelength in the transverse-electric gain narrowing spectra near threshold follows the external feedback wavelength. This indicates that the carrier redistribution in the QD-coupled-quantum well structure is determined by the spectral distribution of the stimulated emission, which can be controlled by external grating.