A method of hybrid integration of quantum dot microdisk lasers with silicon wafer is proposed and realized. In addition to the possibility of combining microlasers with various silicon-based electronic and photonic devices, this makes it possible to significantly improve heat removal from the active region of the microlaser. The thermal resistance normalized to the mesa area reaches the level of about 0.002 (K/W)*cm2, which is significantly lower than the corresponding values of QD microlasers on GaAs substrate and monolithically grown on Si. As a result, the threshold current as well as current-induced shift of emission wavelength are reduced in continuous-wave regime.
Lasers based on semiconductor whispering gallery mode (WGM) resonators represent a perfect platform for active small footprint high-sensitive devices for biodetection. Biochemical samples typically require aqueous solution, and the resonator should be placed into a cuvette with water or in a microfluidic chip. The characteristics of modern semiconductor WGM lasers with an active region based on InAs/InGaAs quantum dots (QDs) make them promising for creating compact highly sensitive devices for biodetection. Deep localization of carriers in InAs/InGaAs QDs and suppressed lateral migration helps us to obtain room-temperature lasing in microdisk lasers immersed in an aqueous medium. In this work, we studied the sensitivity of the microdisk laser resonance spectral position to the refractive index of the surrounding material by changing the salinity of the water solution. We also successfully detected model proteins (secondary antibodies attached to the microdisk surface) via measurement of the lasing threshold power. The proteinprotein interaction on the microdisk surface manifests itself by an increase in the laser threshold power. Thus, in this work we demonstrated, for the first time, the possibility of using QD semiconductor microdisk lasers for detection of proteins in a microfluidic device.
We show that using dense arrays of InGaAs quantum well-dots enables uncooled high-frequency applications with a GHz-range bandwidth. A maximum 3-dB modulation frequency of about 6 GHz was found. The K-limited maximal frequency of 13 GHz was estimated from the modulation response analysis. The experimental values of the energy-todata reaches 1.5 pJ/bit for the smallest diameter under study (10 μm). A 23 μm in diameter microlaser exhibits open eye diagram up to 12.5 Gbit/s and is capable of error-free 10 Gbit/s data transmission at 30°C without temperature stabilization. Our results demonstrate the potential to achieve miniature high-speed on-chip light sources for optical communication applications using lasers with a diameter of only a few micrometers.
A combination of high operation temperatures and small sizes of diode lasers directly grown on silicon substrates is essential for their application in future photonic integrated circuits. In this work, we report on electrically-pumped III-V microdisk lasers monolithically grown on Si substrates with active regions of two kinds: either an InGaAs/GaAs quantum well (QW) or InAs/InGaAs/GaAs quantum dots (QDs). Microdisk resonators were defined using photolithography and plasma chemical etching. The active region diameter was varied from 11 to 31 µm. Microlasers were tested without external cooling at room and elevated temperatures.
The QW laser structure was epitaxially grown by MOCVD on silicon (100) with an intermediate MBE-grown Ge buffer. Under pulsed injection (0.5-µs-long injection pulses with 150 Hz repetition rate), lasing is achieved in QW microlasers with diameters of 23-31 µm with a minimal threshold current density of 28 kA/cm^2. Quasi-single mode lasing (SMSR is up to 20 dB) is observed with emission wavelength around 988 nm. To the best of our knowledge, this is the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. Quantum wells are typically characterized by high optical gain and high direct modulation bandwidth, which can be important in view of further miniaturization of microlasers and their future application. The sidewall passivation can be helpful to reduce the threshold current.
As compared to QWs, quantum dots demonstrate reduced sensitivity to threading dislocations and other crystalline defects as well as to sidewall recombination owing to a suppressed lateral transport of charge carriers which prevents their diffusion towards non-radiate recombination centers. The QD laser structure was directly grown by MBE on Si (001) substrate with 4° offcut to the [011] plane. QD microlasers were tested at room temperature in CW regime with a DC current varied from 0 to 50 mA and at elevated temperatures under CW and pulsed excitation (0.5-µs-long injection pulses with 10 kHz repetition rate). The InAs/InGaAs QDs active region provides the wavelengths in the 1.32–1.35 µm spectral interval. At room temperature, lasing is achieved in microlasers with diameters of 14-30 µm with a minimal threshold current density of 600 A/cm2 (compare with that of 427 A/cm2 in edge-emitting laser). The threshold current density and specific thermal resistance of 0.004 °C×cm^2/mW are comparable to those of high-quality QD microdisk lasers on GaAs substrates. Lasing wavelength demonstrates low sensitivity to current-induced self-heating. Lasing is single mode (SMSR 20 dB) with a dominant mode linewidth as narrow as 30 pm. Under CW excitation lasing sustains up to 60 °C in microlasers with diameter of 30 µm. Because of self-heating, an actual temperature of the active region is close to 100°C. Under pulsed excitation, the maximal lasing temperature is 110°C. To our best knowledge, these are the smallest microlasers on silicon operating at such elevated temperatures ever reported. Up to 90°C lasing proceeds on the ground state optical transition of QDs with wavelength about 1.35 µm. At higher temperatures, lasing wavelength jumps to the excited state transition.
The ability to create metamorphic hybrid heterostructure of 1300 nm spectral band VCSEL is demonstrated. Metamorphic semiconductor part of heterostructure with GaAs/AlGaAs DBR and InAlGaAs/InGaAs QW active region has been grown by molecular beam epitaxy (MBE) on GaAs (100). Top dielectric SiO2/Ta2O5 DBR is made by the magnetron sputtering method. VCSEL has been studied under optical pumping (λ = 532 nm, diameter of the focused laser beam of ~ 1 μm) by using micro-PL setup in the range of optical pump power 0 – 70 mW at room temperature. Presence of the superlinear PL intensity growth having threshold-like dependence of PL integral intensity together with the PL peaks narrowing and mode composition modification with the pumping density increasing could be attributed to lasing behavior of the structure. Obtained results indicate the opportunity to use metamorphic growth on GaAs substrates for the 1300 nm range VCSEL manufacturing.
In this work, electrically-injected microdisk lasers with diameter varied from 15 to 31μm based on an InAs/InGaAs QD
active region have been fabricated and tested in continuous wave regime. At room temperature, lasing is achieved at
wavelength around 1.26…1.27 μm with threshold current density about 900 A/cm2. Specific series resistance is
estimated to be about 10-4 Ohm•cm2. The lasers were tested at elevated temperatures. Lasing is achieved up to 100°C
with threshold current of 13.8mA and lasing wavelength of 1304nm in device with 31μm diameter. To the best of our
knowledge, this is the highest CW lasing temperature and the longest lasing wavelength ever reported for injection QD
microdisk/microring lasers on GaAs substrates. Emission spectrum demonstrates single-mode lasing with side mode
suppression ration of 24dB and dominant mode linewidth of 35pm. The far field radiation pattern demonstrates two
narrow maxima off the disk plane. A combination of device characteristics achieved (low threshold, long wavelength,
operation at elevated temperatures) makes them suitable for application in future optoelectronic circuits for optical
interconnect systems.
In this study, we have investigated metal-organic vapor phase epitaxial nano-patterned selective area growth of InGaAs/InP on non-planar (001) InP surfaces. Due to high etching resistance and the small molecular size of negative tone electron beam HSQ resist, the protection mask formed in HSQ has small feature sizes in ten nanometers scale and allow realization of in-situ etching. As was observed in the SAG regime, in-situ etching of InP by carbon tetrabromide leads to formation of self-limited structures. By altering etching time, the groove shape can be changed from a triangular trench to a trapeze. Another appealing aspect of in situ etching is that the shape of InGaAs can be tuned from a crescent to a triangular or a line by varying growth parameters. Quantum well wires can be fabricated by growing directly in the bottom of V-shaped groove. In addition, changes of mask orientations lead to anistropic or isotropic character of etching. The investigated technique of nano-patterned selective area growth allows obtaining different profiles of structures and different quantum structures such as quantum well or wires in the same growth run. To investigate the shape and crystalline quality of the active material, the cross-sectional geometry was observed by field emission scanning electron microscopy and scanning transmission electron microscopy. The optical properties were carried out at room temperature using micro-photoluminescence setup. The results showed different deposition rates for openings oriented along [0-11] and [0-1-1] directions with higher rate along [0-1-1]. The fabricated active material was incorporated into photonic crystal waveguides.
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.
KEYWORDS: Photonic crystals, Laser crystals, Waveguides, Semiconductor lasers, Refractive index, Crystals, Reflectivity, High power lasers, Gallium arsenide, Near field optics
High concentration of optical power in a narrow exit angle is extremely important for numerous applications of laser diodes, for example, for low-cost fiber pumping and coupling, material processing, direct frequency conversion, etc. Lasers based on the longitudinal photonic band crystal (PBC) concept allow a robust and controllable extension of the fundamental mode over a thick multi-layer waveguide region to achieve a very large vertical optical mode spot size and, consequently, a very narrow vertical beam divergence. Many undesirable effects like beam filamentation, lateral multimode operation and catastrophic optical mirror damage (COMD) are strongly reduced. 650 nm GaInP/GaAlInP PBC lasers show narrow far field pattern (FWHM~7°) stable up to the highest output powers. Differential efficiency up to 85% is demonstrated. Total single mode output power as high as 150 mW is achieved in 4 μm-wide stripes in continuous wave operation, being limited by COMD due to not passivated facets. The lateral far field FWHM is 4 degrees. 840 nm GaAs/GaAlAs PBC lasers show a vertical beam divergence of 8° (FWHM) and a high differential efficiency up to 95% (L=500 μm). A total single mode CW power approaches 500 mW for 1 mm-long 4 μm-wide stripes devices at ~500 mA current, being COMD-limited. The lateral far field FWHM is 5 degrees. Another realization of a longitudinal PBC laser allows lasing in a single high-order vertical mode, a so-called tilted mode, which provides wavelength selectivity and substantially extends the possibility to control the thermal shift of the lasing wavelength. In a multilayer laser structure, where the refractive index of each layer increases upon temperature, it is possible to reach both a red shift of the lasing wavelength for some realizations of the structures, and a blue shift for some others. Most important, the absolute thermal stabilization of the lasing wavelength of a semiconductor laser can be realized.
Recent achievements in self-organized quantum dots (QDs) have demonstrated their potential for long-wavelength laser
applications. However, the wavelength of QD structures pseudomorphically grown on GaAs substrate is typically not
longer than 1.3 μm. In this work we study a novel approach for extension of the spectral range of GaAs-based diode
lasers up to 1.5 μm. We use a sensitivity of QD emission to the band gap energy of surrounding matrix. The method is
based on formation of a QD array inside a metamorphic InGaAs epilayer. Growth regimes of metamorphic buffer that
enable mirror-like surface morphology in combination with effective dislocation trapping are discussed. Structural and
optical properties of metamorphic InAs/InGaAs QDs are presented. It is shown that the wavelength of QD emission can
be controllably tuned in the 1.37-1.58 μm range by varying the composition of metamorphic InGaAs matrix. Details of
formation, fabrication, and characterization of metamorphic-based diode lasers are also presented. We demonstrate a
lasing wavelength as long as 1.48 μm in the 20-80 °C temperature interval. The minimum threshold current density is
800 A/cm2 at RT. The external differential efficiency and pulsed power maximum exceed 50% and 7 W, respectively.
We report on lasers and light emitting diodes based on the longitudinal photonic bandgap crystal (PBC) concept. The PBC design allows achieving a robust and controllable extension of the fundamental mode over a thick multi-layer waveguide region to obtain a very large vertical optical mode spot size and a very narrow vertical beam divergence. An efficient suppression of high order modes can be realized either by the optical confinement factor selection of the fundamental mode, which is localized at the "optical defect" region and has a higher overlap with the gain region. All the other modes spread across the thicker PBC waveguide. In another approach leakage loss selection can be used to suppress excited modes in case of absorbing substrate or the substrate with a higher-refractive index. In this paper we concentrate on growth and performance of high power single mode visible (650 nm) GaInP/AlGaInP PBC lasers, giving a comprehensive example. The devices show narrow far field pattern (full width at half maximum of vertical beam divergence of about 7°), which is stable up to the highest output powers. Differential efficiency up to 85% is demonstrated. Total continuous wave single mode output power as high as 120 mW is achieved in 4 micrometer-wide stripes. Infrared (980 nm) InGaAs/AlGaAs PBC lasers with a beam divergence down to 4.2 degrees and a high temperature stability of the threshold current are also demonstrated.
Optical properties of GaAsN/GaAs heterostructures with different N contents grown by molecular-beam epitaxy were investigated. We show that under the certain grows reigmes the optical properties of the GaAsN layers are determined by recombination via localized states which is due to composition fluctuation. An increase in the N concentration leads to increase in composition fluctuation and, correspondingly, to increase in energy of localized states. Thermal annealing reduces nonuniformity distribution of nitrogen atoms. In short-period GaAsN/GaAs superlattice the effects of phase separation can be enhanced.
Development of submonolayer deposition technique can offer significant flexibility in creation of strained heterostructures of different types and material systems. It was found that under certain growth conditions the deposition of InAs insertions of less than 1 monolayer (ML) thickness in GaAs matrix forms so-called sub-monolayer quantum dots (SML QDs). The energy spectrum of these QDs can be varied over a wide range by tuning the InAs coverage and the thickness of GaAs spacers. Stranski-Krastanow (In,Ga)As QDs (SK QDs), which have been investigated in more details, have proved theoretically predicted lower threshold current density of 26 A/cm2 in compare with QW lasers. However, strong size variation of SK QDs in combination with the relatively low sheet density leads to low peak gain achievable in the ground state. This problem is the reason of typically low efficiency of SK QD-based lasers. Due to higher gain, SML QDs have proved their potential for high power laser application. In this presentation we report on further progress in the technology of SML QD lasers demonstrating high output power (6W) from 100-μm-wide laser diode emitting at 0.94 μm. High power QW-based lasers of the state-of-the-art performance are also presented for comparison.
D. Sizov, N. Kryzhanovskaya, A. Gladyshev, Yu Samsonenko, G. Cirlin, N. Polyakov, V. Egorov, A. Tonkih, Yu Musikhin, Anrei Tsatsul'nikov, N. Ledentsov, Victor Ustinov
Optical and structural properties of self organized InGaAs quantum dots (QD), deposited in Al0.3Ga0.7As matrix, were investigated. Samples were grown by molecular-beam epitaxy (MBE). It is shown, that deposition of 1.7 - 4 monolayer of InAs on Al0.3Ga0.7As surface results in formation of nanoscale QDs on 1 - 2 monolayer thick wetting layer (Stranski-Krastanov growth mode). Large exciton localization energy of the InAs QDs in Al0.3Ga0.7As in compare with QDs in GaAs is demonstrated. This is due to increase in size of these QDs and significant bandgap offset in the case of InAs/AlGaAs system in compare with InAs/GaAs one.
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