Victor M. Ustinov

InGaAs-GaAs quantum-dot lasers

Quantum-dot (QD) lasers provide superior lasing characteristics compared to quantum-well (QW) and QW wire lasers due to their delta like density of states. Record threshold current densities of 40 A/spl middot/cm/sup -2/ at 77 K and of 62 A/spl middot/cm/sup -2/ at 300 K are obtained while a characteristic temperature of 385 K is maintained up to 300 K. The internal quantum efficiency approaches values of /spl sim/80 %. Currently, operating QD lasers show broad-gain spectra with full-width at half-maximum (FWHM) up to /spl sim/50 meV, ultrahigh material gain of /spl sim/10/sup 5/ cm/sup -1/, differential gain of /spl sim/10/sup -13/ cm/sup 2/ and strong nonlinear gain effects with a gain compression coefficient of /spl sim/10/sup -16/ cm/sup 3/. The modulation bandwidth is limited by nonlinear gain effects but can be increased by careful choice of the energy difference between QD and barrier states. The linewidth enhancement factor is /spl sim/0.5. The InGaAs-GaAs QD emission can be tuned between 0.95 /spl mu/m and 1.37 /spl mu/m at 300 K.

Quantum dot lasers

We presents both edge emitting and surface emitting quantum dot laser research. Growth is by both MOCVD and MBE.

GaAs-based long-wavelength lasers

The present paper reviews recent achievements in the fabrication of diode lasers for the near-infrared range on GaAs substrates. 1.3??m light emitters are currently widely used in fibre-optic communication systems. GaAs-based devices are potentially advantageous compared to their InGaAsP counterparts in several aspects, such as improvement of thermal stability, possibility to grow vertical-cavity surface-emitting lasers in a single growth run and the use of large-area high-quality inexpensive GaAs substrates. Three main approaches have been suggested so far to achieve the 1.3??m emission from structures grown on GaAs substrates. They are InGaAs and GaAsSb quantum wells, GaInAsN quantum wells and InAs/GaAs quantum dots. In the present paper we discuss all these approaches including material growth, optical properties and laser characteristics. The results obtained by these methods are compared and their potential advantages discussed.

Negative characteristic temperature of InGaAs quantum dot injection laser

The range of negative characteristic temperatures in temperature dependences of threshold current density of low-threshold (In, Ga)As/(Al, Ga)As quantum dot injection lasers has been observed. A model describing the decrease in threshold current density with temperature at low temperatures is proposed.

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

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.

Self-Organized InGaAs Quantum Dots for Advanced Applications in Optoelectronics

We report on the fabrication of quantum dot (QDs) heterostructures for applications in optoelectronics. Different kinds of QDs are currently used: (i) three-dimensional quantum dots obtained by Stranski-Krastanow or Volmer-Weber growth in the InAs–GaAs material system, (ii) two-dimensionally-shaped QDs formed by submonolayer insertions in the InAs–GaAs and similar systems, (iii) GaAs QDs formed on a corrugated (311)A AlAs surface, (iv) and QDs obtained by spinodal decomposition and activated spinodal decomposition in InGaAs–GaAs and InGaAsN–GaAs material systems. Formation of uniformly sized and shaped QDs is possible in all of these approaches and is mostly governed by thermodynamics. Ultrahigh modal gain and giant optical nonlinearity can be achieved in dense arrays of very small QDs. Long wavelength (1.3–1.6 µm) emission can be achieved using large InAs QDs. Recent advances in growth have made possible the realization of GaAs 1.3 µm continuous wave (CW) vertical-cavity surface-emitting lasers (VCSELs) with ~ 0.8 mW output power and long operation lifetime.

Long-wavelength (1.3-1.5 micron) quantum dot lasers based on GaAs

The molecular beam epitaxy of self-assembled quantum dots (QDs) has reached a level such that the principal advantages of QD lasers can now be fully realized. We overview the most important recent results achieved to date including excellent device performance of 1.3 μm broad area and ridge waveguide lasers (Jth<150A/cm2, Ith=1.4 mA, differential efficiency above 70%, CW 300 mW single lateral mode operation), suppression of non-linearity of QD lasers, which results to improved beam quality, reduced wavelength chirp and sensitivity to optical feedback. Effect of suppression of side wall recombination in QD lasers is also described. These effects give a possibility to further improve and simplify processing and fabrication of laser modules targeting their cost reduction. Recent realization of 2 mW single mode CW operation of QD VCSEL with all-semiconductor DBR is also presented. Long-wavelength QD lasers are promising candidate for mode-locking lasers for optical computer application. Very recently 1.7-ps-wide pulses at repetition rate of 20 GHz were obtained on mode-locked QD lasers with clear indication of possible shortening of pulse width upon processing optimization. First step of unification of laser technology for telecom range with QD-lasers grown on GaAs has been done. Lasing at 1.5 μm is achieved with threshold current density of 0.8 kA/cm2 and pulsed output power 7W.

Multi-Stacked InAs/InGaAs/InP Quantum Dot Laser (Jth=11 A/cm2, λ=1.9 µm (77 K))

Self-organized InAs quantum dots inserted in an (In, Ga)As matrix lattice matched to InP substrate were used as an active region of an injection laser. Low threshold (11 A/cm2) lasing at 1.9 nm (77 K) via the quantum dot states was realized. Temperature dependencies of the main laser parameters demonstrate the important role of the nonradiative recombination. An analysis of basic mechanisms of leakage shows that the Auger recombination share is negligible.