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Focused ion beam is applied to quantum dot based microresonators to form pits or groove on their surface. The emission spectra of the resonators based lasers are significantly thinned out after the ion beam milling, and one or two modes become dominant instead of a group of modes having comparable intensities. The linewidth of the lasing mode is kept unchanged, whereas the lasing threshold demonstrates an insignificant growth.

We report on InGaAs/GaAs quantum dot injection microdisk lasers laterally connected with a bus waveguide fabricated by planar technology from the same epi-structure. Various coupling schemes of microlaser with waveguide are studied including a microlaser attached to a waveguide (zero gap), a 100 nm gap for evanescence light outcoupling, and with a waveguide surrounding the resonator. The modes outcoupling and microlaser's loss (Q-factor) are analyzed by simulation of the lasers. A strong decrease in the number of the microdisk resonance lines associated with an increase in loss in the resonator due to the coupling with waveguide is observed in modeling and experimentally. We study the spectral and lasing parameters of the microdisk lasers, as well as characteristics of the outcoupled emission, and demonstrate efficient light outcoupling for 30 and 40 μm diameter continuous wave operating microdisk laser up to 96 °C. [ABSTRACT FROM AUTHOR]

A technique is proposed for determining the temperature of a laser diode operating in a continuous mode, as well as thermal resistance of the device by comparing its current-voltage characteristic with pulsed current-voltage characteristics measured at different temperatures. The technique was applied to a ∅200 μm half-disk microlaser with an active region based on InGaAs/GaAs quantum dots. It was found that at currents corresponding to the peak laser power and lasing quenching due to overheating of the active region, the device temperature reaches 101 and 149°C, respectively. The thermal resistance of the laser is 110 K/W. [ABSTRACT FROM AUTHOR]

The energy-to-data ratio (EDR) was evaluated for quantum-dot based microdisk laser directly modulated without external cooling. The experimental values of EDR decrease with decreasing diameter of the microdisk and reach 1.5 pJ/bit for the smallest diameter under study (10.5 μm). In larger microdisks (with a diameter greater than 20 μm), the EDR varies in proportion to the square of the diameter. If this relationship were true for smaller microdisks as well, an EDR value of about 100 fJ would be achieved with a diameter of 4 μm. The observed deviation of EDR from the quadratic dependence on the diameter is associated with an increase in the threshold current density in smaller devices, which in turn may be caused by the contribution of nonradiative recombination on the microresonator sidewalls formed by deep etching. [ABSTRACT FROM AUTHOR]

The dependence of the spectral position of the lasing line of a microdisk laser with InAs/InGaAs/GaAs quantum dots on the refractive index of an aqueous solution in which the microlaser is immersed is studied. A maximum resonance shift of 9.4 nm/RIU was obtained for 10-μm-diameter microlasers immersed in an aqueous glucose solution. [ABSTRACT FROM AUTHOR]

The energy consumption of a microdisk laser with InGaAs/GaAs quantum well-dots at high-frequency modulation without forced cooling has been investigated. The lowest energy consumption for a microlaser 20 μm in diameter is estimated to be 1.6 pJ per data bit transferred using an optical signal. [ABSTRACT FROM AUTHOR]

Edge-emitting lasers with active regions based on novel InGaAs/GaAs quantum heterostructures of transitional dimensionality, i.e., quantum well-dots, which are intermediate in properties between quantum wells and quantum dots, are studied. It is shown that the rate of the lasing-wavelength blue shift decreases with increasing number of quantum well-dot layers in the active region and with increasing optical confinement factor as the cavity length decreases. In a laser with 10 quantum well-dot layers, the lasing-wavelength position remains within the limits of the fundamental optical transition down to the smallest cavity lengths (100 μm). In devices with a single quantum well-dot layer and/or with a low optical confinement factor, lasing directly switches from the ground state to waveguide states omitting excited states below ≤200 μm. Such an effect has not been observed in quantum-well- and quantum-dot lasers and can be attributed to the abnormally low density of excited states in quantum well-dots. [ABSTRACT FROM AUTHOR]

The feasibility of detecting the emission of a microdisk laser with a diameter of 23 μm with an active region based on InGaAs/GaAs quantum well-dots using a nearby photodetector (100 × 4000 μm) with a similar active region is demonstrated. For continuous lasing, a pump current of 20 mA, and a distance between the faces of the microlaser and the photodetector of about 100 μm, a photocurrent of ~10 μA was obtained, which corresponds to a photodetector sensitivity of ~0.9 μA/μW. [ABSTRACT FROM AUTHOR]

The operation speed of microdisk lasers with quantum dots working at room temperature without thermal stabilization has been experimentally examined, and the widest modulation bandwidth of microdisks with various diameters has been calculated. It was shown that taking into account the effect of self-heating of a microlaser at high bias currents, which is manifested in a decrease of the ultimate operation speed and in an increase in the current at which the widest modulation bandwidth is reached, enables a good description of the experimental data. The self-heating most strongly affects microlasers with a small diameter (less than 20 μm). [ABSTRACT FROM AUTHOR]

A model is developed that makes it possible to analytically determine the threshold current of a microdisk laser with consideration for its self-heating as a function of the ambient temperature and the microlaser diameter. It is shown that there exists a minimum microdisk diameter determined by self-heating, up to which continuous-wave lasing can be reached at a given temperature. Another manifestation of the self-heating effect is the existence of the ultimate working temperature, which is lower, the smaller the microlaser diameter. Reasonable agreement between the predictions of the model and the available experimental data is shown. [ABSTRACT FROM AUTHOR]

The results of comparative analysis of the spectral and threshold characteristics of room-temperature injection microdisk lasers of the spectral range 1.2×× μm with different active regions, notably, InGaAsN/GaAs quantum wells or InAs/InGaAs/GaAs quantum dots are presented. It is found that microlasers of a comparable size with quantum wells possess a larger laser generation threshold when compared with microlasers with quantum dots. At the same time, the latter are characterized by a noticeably smaller fraction of emitted power corresponding to laser modes. The jump to lasing via an excited-state optical transition is also characteristic for them. Microdisk lasers based on InGaAsN alloy do not have these disadvantages. [ABSTRACT FROM AUTHOR]

Lasing in the orange spectral range (599–605 nm) is demonstrated for (AlxGa1 –x)0.5In0.5P–GaAs laser diodes grown by metalorganic vapor-phase epitaxy (MOVPE) on GaAs (211)A and (322)A substrates. The active region consists of four layers of InxGa1 –xP vertically coupled quantum dots. The leakage of nonequilibrium electrons from the active region is suppressed by barriers consisting of four quantum-confinement layers of the InGaAlP solid solution with a high Ga content. The maximal optical output power in the pulsed regime is 800 mW and is limited by the catastrophic optical degradation of mirrors. The lasers fabricated from structures grown on (322)A substrates have a lower threshold current density, higher differential quantum efficiency, and smaller internal losses when compared with lasers fabricated from structures grown on (211)A substrates, which is explained by the higher barrier for nonequilibrium electrons in the first case. [ABSTRACT FROM AUTHOR]

Microdisk lasers 10–30 μm in diameter operating at room temperature without thermal stabilization and with an active region based on nanostructures of hybrid dimensionality—quantum wells–dots—are investigated. High-frequency measurements of the microlaser response are performed in the direct small-signal modulation mode, which makes it possible to establish the parameters of the operating speed and analyze their dependence on the microlaser diameter. It is found that the K factor is (0.8 ± 0.2) ns, which corresponds to optical losses of ~6 cm–1, and no regular dependence on the diameter is observed. It is found that the low-frequency component of the damping coefficient of relaxation oscillations is inversely proportional to the diameter. This character of the dependence evidences a decrease in the carrier lifetime in small-diameter microcavities, which can be associated with the prevalence of nonradiative recombination on their side walls. [ABSTRACT FROM AUTHOR]

A post-growth technique aimed at spatial modification of facet reflectance of edge-emitting diode lasers has been proposed. It is based on the deposition of an anti-reflection coating and subsequent precise etching with a focused ion beam. The technique allowed suppressing of high-order lateral modes in 10 μm stripe lasers based on ten layers of InAs/InGaAs quantum dots. [ABSTRACT FROM AUTHOR]

The influence of the modulation p-doping level on multi-state lasing in InAs/InGaAs quantum dot (QD) lasers is studied experimentally for devices having various external losses. It is shown that in the case of short cavities (high external loss), there is an increase in the lasing power component corresponding to the ground-state optical transitions of QDs as the p-doping level grows. However, in the case of long cavities (small external loss), higher dopant concentrations may have an opposite effect on the output power. Based on these observations, an optimal design of laser geometry and an optimal doping level are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate a record low threshold current density of 250 A/cm2 in a quantum dot microdisk laser with a 31-μm diameter operating at room temperature in continuous wave regime without temperature stabilization. This low threshold current density is very close to the transparency current density estimated in broad-area edge-emitting lasers made of the same epitaxial wafer. [ABSTRACT FROM AUTHOR]

Injection microlasers with an active region based on arrays of InGaAs/GaAs quantum well-dots, formed by deep etching, have been studied. The manner in which the current–voltage characteristic changes when the diameter microlaser is reduced shows that a nonelectrically conducting layer with thickness of about 1.5 μm is formed near the side surface, which leads to a decrease in the effective current flow area. [ABSTRACT FROM AUTHOR]

We have studied characteristics of a 23-μm-diameter microdisk laser operating in a regime of direct high-frequency modulation at a stabilized heat-sink temperature of 18°C. It is found that the minimum energy consumption in this regime amounts to ~1.6 pJ/bit and is achieved at a modulation frequency of 4.2 GHz. The maximum modulation frequency is 6.7 GHz, at which the minimum energy consumption is 3.3 pJ/bit. [ABSTRACT FROM AUTHOR]

Vertical-cavity surface-emitting lasers (VCSELs) with an active region based on sub-monolayer InGaAs quantum dots and doped AlGaAs/GaAs distributed Bragg reflectors were grown by MBE. VCSELs with current aperture of 3 µm in diameter demonstrate single-mode lasing in 980-nm range with the threshold current of 0.6 mA, maximum output power up to 4 mW, and external differential efficiency of 68%. Multimode VCSELs with a (10–12)-µm aperture demonstrate ultralow internal optical loss of 0.09% per pass, which compares favorably with the best results obtained in similar lasers with undoped distributed Bragg reflectors. [ABSTRACT FROM AUTHOR]

Raman scattering spectroscopy is used to study the process of selective oxidation of Al0.97Ga0.03As layers. Stresses arising in GaAs/(AlGa)xOy layers as a result of selective oxidation under different conditions are determined. The effects of local heating of the samples with laser radiation during measurements of the Raman signals, photoresist hardening resulting from the oxidation, and overoxidation are analyzed. The instrumentation and method of selective oxidation are optimized; as a result, arrays of vertical-cavity surface-emitting lasers are fabricated. The active region of these lasers is based on two InGaAs quantum wells with top oxidized and bottom semiconductor distributed Bragg reflectors. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The design and fabrication technology for integrated arrays for vertical-cavity surface-emitting lasers with bottom AlGaAs/GaAs semiconductor and top AlGaO/GaAs distributed Bragg reflectors is suggested. Arrays containing 8×8 lasers with an active region based on two InGaAs quantum wells were produced. Individual emitters with an oxidized aperture of 8–10μm in diameter demonstrate cw lasing at 960–965 nm at room temperature, with a threshold current of 1.0–2.5 mA, external efficiency of up to 0.4 mW/mA, and a maximum output power of over 2 mW. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Diode lasers based on several layers of self-organized quantum dots (QD) on GaAs substrates were studied. The lasing wavelength lies in the range λ = 1.25-1.29 μm, depending on the number of QD layers and optical losses. A record external differential efficiency of 88% and the characteristic temperature of threshold current, 145 K, were obtained. The internal losses, and also threshold and spectral characteristics, are correlated with the optical gain and radiative recombination efficiency, which are strongly dependent on the design of the active region and growth modes. [ABSTRACT FROM AUTHOR]

The design of the active region in InGaAsN quantum well (QW) injection lasers is investigated. Long-wavelength (1.27–1.3 mm), low-threshold (<400 A/cm2), and high-efficiency (>50%) lasing is obtained at room temperature from structures based on single InGaAsN QWs in GaAs or InGaAsN barrier layers. The principal parameters (threshold, temperature, power) of these lasers have been studied in the wide-stripe configuration. The characteristics of injection lasers with different designs of the active region are compared. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]