Yuri M. Shernyakov

InGaAs/GaAs Quantum Dot Lasers with Ultrahigh Characteristic Temperature (T 0= 385 K) Grown by Metal Organic Chemical Vapour Deposition

Low threshold current density (AlInGa)As/GaAs lasers based on InGaAs quantum dots (QDs) are grown by metal organic chemical vapour deposition (MOCVD). Quantum dots deposited at 490° C and covered with GaAs are directly revealed in the active region. On a transmission electron microscopy (TEM) image of the laser structure no large clusters or dislocations are found over a macroscopic distance. We show that the properties of QD lasers can be strongly improved if the QDs are confined by Al0.3Ga0.7As barriers and the cladding layers are grown at high temperature. Optimisation of the laser structure geometry allows extension of the range of ultrahigh temperature stability (T0=385 K) of the threshold current to 50° C.

Progress in Quantum Dot Lasers : 1100 nm, 1300 nm, and High Power Applications

Quantum dot (QD) lasers have decisive advantages compared to quantum well lasers. Zero-dimensional charge carrier localization and reduction of charge carrier diffusion result in reduced non-radiative surface recombination and thus possibly reduced facet overheating and larger catastrophic optical damage (COD) threshold, crucial for high power operation. The emission wavelengths of 1100 nm?1300 nm are easily realized using QDs on GaAs substrate, not available with traditional quantum wells of the same material system. We present results on metal-organic chemical vapor phase deposition (MOCVD) and molecular beam epitaxy (MBE) grown high power QD lasers (up to 4 W front facet cw) based on InGaAs QDs on GaAs substrate

Vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

Molecular beam epitaxy-grown 0.98-mum vertical-cavity surface-emitting lasers (VCSELs) with a three-stack submonolayer (SML) InGaAs quantum-dot (QD) active region and fully doped AlxGa 1-xAs-GaAs DBRs was studied. Large-aperture VCSELs demonstrated internal optical losses less than 0.1% per one pass. Single-mode operation throughout the whole current range was observed for SML QD VCSELs with the tapered oxide apertures diameter less than 2 mum. Devices with 3-mum tapered-aperture showed high single-mode output power of 4 mW and external quantum efficiency of 68% at room temperature

Sulfur passivation of InGaAs/AlGaAs SQW laser (977 nm) facets in alcohol-based solutions

Abstract Sulfide treatment of InGaAs/AlGaAs SWQ lasers ( λ = 977 nm) in alcohol-based solutions increases the catastrophic optical damage limit. This increase is largest (50%) when the solvent with the lowest dielectric constant ( tert -butanol) is used.

High-power high-brightness semiconductor lasers based on novel waveguide concepts

We have designed, fabricated and measured the performance of two types of edge emitting lasers with unconventional waveguides and lateral arrays thereof. Both designs provide high power and low divergence in the fast and the slow axis, and hence an increased brightness. The devices are extremely promising for new laser systems required for many scientific and commercial applications. In the first approach we use a broad photonic crystal waveguide with an embedded higher order mode filter, allowing us to expand the ground mode across the entire waveguide. A very narrow vertical far field of ~ 7° is resulting. 980 nm single mode lasers show in continuous wave operation more than 2 W, ηwp ~ 60%, M2 ~ 1.5, beam parameter product of 0.47 mm×mrad and a brightness ~ 1×108 Wsr-1cm-2 respectively. First results on coherent coupling of several lasers are presented. In the second approach we use leaky designs with feedback. The mode leaks from a conventional waveguide into a transparent substrate and reflects back, such that only one mode at a selected wavelength is enhanced and builds up, others are suppressed by interference. 1060 nm range devices demonstrate an extremely narrow vertical far field divergence of less than 1°.

QD lasers: physics and applications

Quantum dot (QDs) heterostructures structurally represent tiny 3D insertions of a narrow bandgap material, coherently embedded in a wide-bandgap single-crystalline matrix. The QDs are produced by conventional epitaxial techniques applying self-organized growth and behave electronically as artificial atoms. Strain-induced attraction of QDs in different rows enables vertically-coupled structures for polarization, lifetime and wavelength control. Overgrowth with ternary or quaternary alloy materials allows controllable increase in the QD volume via the island-activated alloy phase separation. Repulsive forces during overgrowth of QDs by a matrix material enable selective capping of coherent QDs, keeping the defect regions uncapped for their subsequent selective evaporation. Low-threshold injection lasing is achieved up to 1350 nm wavelength at 300K using InAs-GaAs QDs. 8 mW VCSELs at 1.3 μm with doped DBRs are realized. Edge-emitters demonstrate 10 GHz bandwidth up to 70°C without current adjustment. VCSELs show ~4 GHz relaxation oscillation frequency. QD lasers demonstrate above 3000 h of CW operation at 1.5 W at 45°C heat sink temperature without degradation. The defect reduction technique (DRT) applied to thick layers enables realization of defect-free structures on top of dislocated templates. Using of DRT metamorphic buffer layers allowed 7W GaAs-based QD lasers at 1500 nm.

High power lasers based on submonolayer InAs–GaAs quantum dots and InGaAs quantum wells

Broad area lasers based on InAs-GaAs quantum dots formed by submonolayer deposition were fabricated. High modal gain of submonolayer quantum dots permits the use of broad-waveguide and highly doped design. Continuous wave output power of 6 W limited by mirror damage and conversion efficiency of 58% were demonstrated at 20 °C. The characteristic temperature of 150 K was achieved.

Tilted Wave Lasers: A Way to High Brightness Sources of Light

Semiconductor laser diodes are conventionally based on a relatively thin waveguide structure grown epitaxially on a thick single crystalline substrate, wherein the latter serves as a medium for carrier flow and as mechanical support and plays no role in optics. Although earlier attempts to provide the outcoupling of light through a transparent substrate in leaky lasers realized a narrow leaky emission beam, either significant leakage losses led to the deterioration of the laser performance or/and a large fraction of the output optical power was concentrated in a co-existing angularly broad emission peak originating from the narrow active waveguide. Our solution, a tilted wave laser (TWL), includes polishing the back side of the substrate under the stripe providing mirror-like reflection for the leaky mode which can thus exhibit multiple reflection and amplification cycles before exiting the device from the substrate facet. Fulfillment of phase matching conditions allows wavelength-stabilized operation. At a wavelength of 1060 nm TWLs are shown to exhibit a very small thermal shift of the emission wavelength of 0.03 nm/K. A cw output power of 3.3 W for 2 mm long cavities with uncoated facets is obtained, wherein the entire power is concentrated in a single vertical lobe having a full width at half maximum of 0.8°. The scattering of the tilted optical wave by the back substrate surface roughness is modeled and found to be the main mechanism limiting the differential efficiency, wherein the scattering contributes up to 10 cm-1 to the losses for a present roughness of ~30 nm. The free carrier absorption in the n-doped substrate ( ~3 cm-1 for n ~1018 cm-3) dominates for a roughness <; 10 nm.

Quantum dot lasers and relevant nanoheterostructures

Spectral and power characteristics of QD stripe lasers operating in two-state lasing regime have been studied in a wide range of operation conditions. It was demonstrated that neither self-heating nor increase of the homogeneous broadening are responsible for quenching of the ground-state lasing beyond the two-state lasing threshold. It was found that difference in electron and hole capture rates strongly affects light-current curve. Modulation p-type doping is shown to enhance the peak power of GS lasing transition. Microring and microdisk structures (D = 4-9 μm) comprising 1.3 μm InAs/InGaAs quantum dots have been fabricated and studied by μ-PL and NSOM. Ground-state lasing was achieved well above root temperature (up to 380 K). Effect of inner diameter on threshold characteristics was evaluated.

Modeling of photonic-crystal-based high-power high-brightness semiconductor lasers

The concepts, features, modeling and practical realizations of high power high brightness semiconductor diode lasers having ultrathick and ultrabroad waveguides and emitting in the single vertical single lateral mode are analyzed. Ultrathick vertical waveguide can be realized as a photonic band crystal with an embedded filter of high order modes. In a second approach a tilted wave laser enables leakage of the optical wave from the active waveguide to the substrate and additional feedback from the back substrate side. Both designs provide high power and low divergence in the fast and the slow axis, and hence an increased brightness. Lateral photonic crystal enables coherent coupling of individual lasers and the mode expansion over an ultrabroad lateral waveguide. Experimental results are presented. Obtained results demonstrate a possibility for further expansion of the concept and using the single mode diodes having an ultrabroad waveguide to construct single mode laser bars and stacks.