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The fabrication and study of the characteristics of a lattice-matched quantum cascade laser structure on an indium-phosphide substrate, designed for a wavelength of ~4.8 μm corresponding to one of the atmospheric windows are described. The heterostructure grown by molecular-beam epitaxy consisted of thirty cascades. Lasing was experimentally observed at temperatures up to 200 K at a wavelength coinciding with the calculated one, which confirms the high heterointerface quality and high precision of the layer thicknesses and active-region doping levels.

The process of obtaining a modified structure for quantum cascade lasers is studied; this process includes growth using molecular-beam epitaxy, plasma etching, photolithography with the use of liquid etching, and the formation of special contacts for decreasing losses in the waveguide. The use of a special type of structure makes it possible, even without postgrowth overgrowth with a high-resistivity material, to attain parameters satisfying requirements to heterostructures in high-quality quantum cascade lasers at maximal simplification of the entire preparation process.

The driving current, chip area of high-power AlGaInN light emitting diodes (LEDs) and the level of integration of LED arrays are continuously increased to provide ever higher output light flux. The new developments require more attention to pay to the thermal management of LEDs, commonly assessed in terms of the thermal resistance. Temperature distribution in a LED array and its effect on the chip thermal resistance has been studied both theoretically and experimentally. The thermal measurements were performed with the help of a temperature-sensitive parameter - forward voltage drop on the p-n junction under the action of heating current. Two methods of heat exciting were used: step-like or harmonically pulse-width modulated heating current. Analysis of forward voltage relaxation at transient thermal processes allows determination of thermal impedance components corresponding to the structural elements of the LEDs and arrays. The temperature distribution in the LED array predicted by coupled simulations of the heat transfer agrees well with the experimental measured temperature mapping by the IR-microscopy.

Vertical-external-cavity surface-emitting lasers (VECSEL), or semiconductor disk lasers (SDL), are attractive laser source for a wide range of applications owing to unique possibility to combine high output power with an excellent beam quality [1]. The intrinsic features of InAs quantum dots (QD) can offer low threshold, broad wavelength tunability, fast carrier dynamics and low temperature sensitivity. Recently, continuous wave (CW) operation of QD-based VECSEL emitting at 1.25 μm with output powers reaching multi-watt levels were achieved at room temperature [2]. However, extending the emission wavelength to 1.3 μm and beyond becomes more challenging. To date, QD-based VECSEL with optical power greater than 0.5 mW at 1305 nm has been demonstrated [3]. Here, we present a record-high power InAs/InGaAs QD-based VECSEL operating at the wavelength of 1.3 μm.

Optical characteristics of quantum-cascade laser structures were studied in this work. Current-voltage characteristics and dependencies of photoresponse signal on current through the structure were measured together with the spontaneous and stimulated emission spectra. The stimulated emission with wavelength close to 9.56 μm with optical power of tens of milliwatt was observed in a pulsed mode.

The vertical transport in short-period InAs/AlSb and GaAs/AlAs superlattices was studied. The negative differential conductivity was observed in a miniband transport regime as a result of the overlapping of confined states in a periodic quantum well structure (Esaki-Tsu mechanism). Several maxima appeared on current–voltage characteristics of the superlattices found in the non-resonant tunnelling regime. They are shown to be due to the influence of the optical cavity on optical transitions within quantum wells (Purcell effect).

Semiconductor heterostructures with quantum dots (QDs) are experimentally proved to exhibit properties expected for zero-dimensional systems, e.g. ultrasharp luminescence lines up to high temperatures, massively increased exciton oscillator strength per unit volume and temperature insensitivity of the radiative lifetime. When applied to the injection lasers these advantages help to increase strongly material gain, differential gain, to improve temperature stability of the threshold current and to suppress chirp. Threshold current densities as low as 60 A/cm 2 at 300 K are obtained. Formation of QDs with properties satisfying device requirements on QD size, shape, uniformity and density became possible by utilizing self-ordering phenomena on crystal surfaces.

We demonstrate stable mode-locking in a Yb : KYW laser by using a quantum-dot (QD) saturable absorber structure that incorporates a p-n junction. A reduction in the output pulse duration was measured when a reverse bias was applied to the QD saturable absorber mirror.

35GHz passive mode-locking of 1.3μm (InGa)As∕GaAs quantum dot lasers is reported. Hybrid mode-locking was achieved at frequencies up to 20GHz. The minimum pulse width of the Fourier-limited pulses was 7ps with a peak power of 6mW. Low uncorrelated timing jitter below 1ps was found in cross correlation experiments. High-frequency operation of the lasers was eased by a ridge waveguide design that includes etching through the active layer.

Complex influence of photon lifetime (controlled by the mirror loss) and aperture size on the performance of 850 nm InGaAlAs oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with fully doped AlGaAs-based distributed Bragg reflectors (DBR) was investigated. We find a tradeoff between photon lifetime and gain nonlinearity for maximizing the optical bandwidth, leading to the optimum aperture size close to 4-6 μm. In spite of the reduced photon lifetime (from 4 ps to 1 ps), the excess damping caused by the current-induced self-heating limits the ultimate modulation bandwidth for the given VCSELs design at 24-25 GHz. Further improvement in high frequency characteristics can be facilitated by decrease of the heat generation and improvement of the heat removal from the active region as well as by proper engineering of the scattering loss at the oxide aperture while keeping the low capacitance optimizing design of the oxide aperture.

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.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Quantum dot (QD) edge emitting and vertical cavity lasers are realized using a self-organized growth approach. Threshold current densities at room temperature (RT) of about 60 A/cm/sup 2/ for edge emitting and 170 A/cm/sup 2/ for vertical cavity lasers are measured. High internal (>96%) and differential (70%) efficiencies are obtained for InGaAs-AlGaAs lasers based on vertically coupled QDs and RT 1 W continuous wave operation is demonstrated. QD lasers exhibit much larger gain, differential gain and smaller linewidth enhancement factor as compared to conventional quantum well devices.

Pulsed lasing at 1.3 /spl mu/m via the exciton ground state is demonstrated for vertical cavity surface emitting lasers containing three uncoupled sheets of InAs quantum dot active layers. The dots lie within InGaAs quantum wells separated by GaAs barrier layers. The structures are grown on GaAs substrates and when fabricated include selectively oxidized AlO current apertures and AlO/GaAs distributed Bragg reflectors. Experimental devices operate pulsed at 20/spl deg/C with threshold currents below 2 mA and differential slope efficiencies of 40%.

Summary form only given. Vertical cavity surface emitting lasers (VCSELs) emitting at 1.3 /spl mu/m and integrated with GaAs-based microelectronic circuits have many potential applications in optical communication systems. Several approaches exist for the realization of 1.3 /spl mu/m VCSELs. A promising approach for the realization of longer wavelength VCSELs is the use of self-organized InAs-InGaAs quantum dot (QD) active gain regions. In 1997 we demonstrated QD VCSELs on GaAs with peak emission wavelengths near 1.0 /spl mu/m and sub-milliampere threshold currents. We have now extended the QD peak emission wavelength to 1.3 /spl mu/m by selectively varying the physical size and composition of the InAs-InGaAs dots and herein report room temperature continuous wave (CW) 1.3 /spl mu/m QD VCSELs. While striving to maximize the uniformity of the QDs to increase device efficiency at a single emission wavelength, we have also experimented with sheets of QDs wherein the dot size is purposely nonuniform. Though less efficient, these nonuniform QD active regions have potential applications in tunable VCSELs where a broad gain bandwidth is required.

A quantum-dot-based saturable absorber has been demonstrated to initiate the generation of femtosecond pulses from a passively mode-locked solid-state laser. Control and tuning of the pulse duration from 58 ps to 158 fs was achieved. The 158 fs transform-limited pulses at 1280 nm are the shortest pulses that were produced from the Cr:forsterite laser passively mode locked by an InAs/InGaAs quantum-dot semiconductor saturable absorber mirror.

The room-temperature vertical transport in InAs/AlSb and GaAs/AlAs short-period superlattices was studied. The influence of optical cavity on current-voltage characteristics was found in the range of both resonant and nonresonant tunneling. Possible explanations are suggested.

Optical absorption and birefringence due to intersubband electron transitions were investigated in GaAs/AlAs MQW structures. These structures are intended for creation of a mid-infrared laser of a new type. Experimental results on electron redistribution between size-quantization levels under electron heating were obtained up to an electric field of 3500?V?cm-1.