Widely tuned room temperature terahertz quantum cascade laser sources based on difference-frequency generation Appl. Phys. Lett. 101, 251121 (2012) Noise amplification by chaotic dynamics in a delayed feedback laser system and its application to nondeterministic random bit generation Chaos 22, 047513 (2012) Effect of the number of quantum dot layers and dual state emission on the performance of InAs/InGaAs passively mode-locked lasers Appl. Phys. Lett. 101, 251115 (2012) Ultrafast polarization modulation in vertical cavity surface emitting lasers with frequency dependent current injection Appl.

A novel approach to producing p-type ZnSe epitaxial layers is reported which involves nitrogen atom beam doping during molecular beam epitaxial growth. Net acceptor concentrations as large as 3.4×1017 cm−3 have been measured in nitrogen atom beam doped ZnSe/GaAs heteroepitaxial layers which represents the highest acceptor concentration reported to date for ZnSe:N epitaxial material grown by molecular beam epitaxy. In addition, light-emitting diodes based on ZnSe:N/ZnSe:Cl, p-n homojunctions have been found to exhibit dominant electroluminescence in the blue region of the visible spectrum at room temperature.

We have carried out the first detailed structural studies of degradation in II-VI blue-green light emitters. Electroluminescence and transmission electron microscopy studies carried out on light emitting diodes fabricated from quantum well laser structures and electroluminescence studies on stripe laser structures show that degradation occurs by the formation and propagation of crystal defects. The studies indicate that room temperature cw lasing in such structures is possibly prevented by the rapid formation of such defects at the high current densities required for lasing.

The growth of p-ZnSe:N films by molecular-beam epitaxy, employing a free radical nitrogen source, has been investigated. Using this technique we have obtained p-type ZnSe with net acceptor concentrations up to 1.0×1018 cm−3, as measured by capacitance–voltage(C–V) profiling−this is the highest ever reported for p-type ZnSe. By adjusting the flux of active nitrogen and the substrate temperature, films with net acceptor concentrations from 1.0×1016 to 1.0×1018 cm−3 were grown. Evidence of compensation was found in the low temperature photoluminescence and C–V measurements; the degree of compensation depends on the amount of nitrogen incorporated into the film. The dependencies of nitrogen density, net acceptor concentration, and degree of compensation upon the flux of active nitrogen and the substrate temperature are discussed.

The development of compact, reliable and inexpensive short-wavelength lasers is certain to have profound effects on virtually any technology that uses coherent visible light. Although the impact of such devices will be far-reaching, the primary driving force behind efforts to develop blue-green diode lasers is without question optical recording. The demand for increased data storage capabilities is continually forcing the recording industry to increase storage densities.

We have investigated the role of stacking faults in high quality ZnSxSe1−x heterostructures and a ZnSxSe1−x/CdxZn1−xSe based II-VI blue-green quantum well laser structure grown on GaAs substrates. We find that these stacking faults, which originate at the epilayer/substrate interface during the initial stages of the growth, act as sources for misfit dislocation formation in the quantum well region of ZnSxSe1−x/CdxZn1−xSe based devices. We have analyzed the formation mechanism of these dislocations. We also show through cathodoluminescence microscopy that these stacking faults act as nonradiative recombination centers which therefore reduce the luminescence of these devices.

A systematic dependence of the density and type of stacking fault defects with substrate surface chemistry and film growth mode was observed in ZnSe-based films grown on GaAs substrates. Namely, the density of Frank-type stacking faults is very large for films grown on Ga-rich surfaces, but is very low for films grown on As-stabilized surfaces exposed to Zn prior to the growth of the film. In contrast, the density of Shockley-type stacking faults increases for films grown by 3D growth mode at the initial stages of growth, but decreases greatly if the films are grown by the layer-by-layer growth mode. Films with stacking fault densities as low as 104/cm2 were obtained by growing the films by the layer-by-layer growth on GaAs epilayers with As-stabilized surfaces that were exposed to Zn for 1–2 min prior to the growth of the films.

We study the growth of pseudomorphic ZnSSe layers on GaAs. The dependence of the epilayer quality on Zn exposure to the GaAs surface is investigated. Zn treatment prior to the ZnSe buffer growth on the As-rich GaAs surface results in the lowest defect density. Transmission electron microscopy studies show that an atomic scale smooth interface is formed. Based on the etch pit density and photoluminescence image analysis, ZnSSe layers with defect density ≤1×104 cm−2 can be reproducibly obtained.