Mikhail V. Kisin

High power 2.4μm heavily strained type-I quantum well GaSb-based diode lasers with more than 1W of continuous wave output power and a maximum power-conversion efficiency of 17.5%

The authors demonstrate a double quantum well GaSb-based diode laser operating at 2.4μm with a room-temperature cw output power of 1050mW and a maximum power-conversion efficiency of 17.5%. Laser differential gain with respect to current increases by a factor of 2 and laser threshold current is nearly halved when the compressive strain in the quantum wells is increased from 1.2% to 1.6%. This improvement is due to substantially improved hole confinement in the heavily compressively strained active region.

Continuous-wave room temperature operated 3.0μm type I GaSb-based lasers with quinternary AlInGaAsSb barriers

Diode lasers emitting at 3.0μm were designed and fabricated. Device active region contained two compressively strained InGaAsSb quantum wells incorporated in quinternary AlInGaAsSb barriers. Laser output power at room temperature was 130mW in continuous wave regime and more than 1W in pulse.

Phonon enhanced inverse population in asymmetric double quantum wells

Interwell optical-phonon-assisted transitions are studied in an asymmetric double-quantum-well heterostructure comprising one narrow and one wide coupled quantum wells (QWs). We show that the depopulation rate of the lower subband states in the narrow QW can be significantly enhanced thus facilitating the intersubband inverse population, if the depopulated subband is aligned with the second subband of the wider QW, while the energy separation from the first subband is tuned to the highest energy optical-phonon mode.

Influence of complex phonon spectra on intersubband optical gain

Electron-phonon scattering rates and intersubband optical gain spectra were calculated, including the optical phonon confinement effect in AlGaAs/GaAs/AlGaAs quantum well heterostructures. Comparison of the calculated gain spectra with those calculated using the bulk phonon approximation shows that details of the phonon spectrum have a strong influence on the intersubband optical gain.

Widely tunable type-II interband cascade laser

We discuss an ultrawide, voltage-tunable type-II mid-IR interband cascade laser. Its design has a charge accumulation layers outside of the optically active quantum wells that unclamps the electron-hole concentrations and facilitates above-threshold Stark shifts. Our results demonstrate laser tuning of 120nm (120cm−1).

Optical characteristics of III-nitride quantum wells with different crystallographic orientations

This article presents a direct comparison of calculated optical characteristics of polar, nonpolar, and semipolar III-nitride quantum wells. We show that the advantage of using wider quantum wells offered by nonpolar/semipolar technology is severely limited by narrower valence subband separation, thermal hole redistribution, and resulting optical gain degradation in wider wells. However, we emphasize the importance of using wider quantum wells to prevent electron leakage. We also show that gain characteristics of laser structures grown in nonpolar/semipolar orientations are less vulnerable to detrimental effect of nonradiative recombination.

Effect of Quantum Well Compressive Strain Above 1% On Differential Gain and Threshold Current Density in Type-I GaSb-Based Diode Lasers

InGaAsSb/AlGaAsSb quantum well (QW) diode laser structures with either 1% or 1.5% compressively strained QWs were grown on GaSb substrates by molecular beam epitaxy. Wide-stripe lasers fabricated from structures of both types have room-temperature operating wavelengths near 2.3 microns. The room-temperature threshold current density of 1-mm-long uncoated devices with 1.5% strained QWs was lower than threshold current density of the 1.0% strained QW devices by nearly a factor of two (120 A/cm2 versus 230 A/cm2 ). Experiment shows that the reduction in threshold current density with increasing QW strain is related to the increase in differential gain and decrease in transparency current density. Optical gain calculations prove that improvement of the QW hole confinement reduces the threshold carrier concentration in laser structures with heavily strained low arsenic content quantum wells.

Experimental study of the optical gain and loss in InAs/GaInSb interband cascade lasers

Optical gain and loss have been measured in type II InAs/GaInSb interband cascade lasers operating in the 3.4–3.6 μm wavelength range. The maximum temperature of cw operation was found to be limited by strong gain saturation due to active region overheating, while the temperature increase of the total optical loss was relatively small. In devices with a longer lasing wavelength and a thinner substrate-side cladding layer, a strong periodic modulation of the optical gain spectra was observed. This effect is consistent with resonant optical leakage into the substrate.

Optimum quantum well width for III-nitride nonpolar and semipolar laser diodes

The advantage of using wider quantum wells in III-nitride lasers offered by nonpolar/semipolar technology is limited by narrower valence subband separation, thermal hole redistribution, and resulting optical gain degradation in wider wells. We show that corresponding increase in radiative carrier lifetime in wider quantum wells can lower the laser threshold, thus inferring the existence of an optimum quantum well width for laser design.

Effects of interface phonon scattering in three-interface heterostructures

A detailed study of the electron–optical–phonon interaction in an asymmetric one-well/one-barrier heterostructure is given. Dispersion relations and phonon potential distributions for interface phonon modes are derived in the framework of the macroscopic dielectric continuum model. It is found that for intrawell relaxation processes the sum of the scattering rates by all interface polar-optical phonon modes is approximately independent of the width of the barrier layer. Consequently, a simplified Hamiltonian for electron–phonon interaction in a single quantum well can be used for scattering rate calculation in multiple heterointerface structures. The combined scattering rates by interface and confined phonon modes are compared with the results obtained in an idealized model using the bulklike phonon spectrum. The practical invalidity of the latter approximation is shown for electron kinetic energies comparable with the typical energy of optical phonons in the heterostructure.