The electronic structure of self-organized InP/GaP quantum dots ͑QDs͒ has been studied by means of photoluminescence ͑PL͒ measurements as a function of hydrostatic pressure up to 8 GPa, temperature, and laser excitation power. At ambient pressure the PL emission of the sample arises from direct optical transitions between the lowest electron and hole ⌫-point states confined in the QD's. At a very low pressure of about 0.15 GPa, the ⌫-X conduction-band crossover occurs, after which the PL emission of the dots becomes roughly 20 times weaker in intensity and its energy exhibits the slight redshift typical of indirect recombination processes from the conduction-band X valleys. Our results indicate a type-I band alignment for the strained InP/GaP dot structure at low pressure and yield a value of 300Ϯ30 meV for the valence-band offset. Upon further increase in pressure above 1.2 GPa we observe the quenching of the dot emission, which is taken as evidence for a type-I-type-II transition.

The design and implementation of a short-wavelength quantum-cascade laser based on the strain-compensated In0.73Ga0.27As–In0.55Al0.45As–AlAs heterosystem on InP is described. Lasers with a reduced level of doping in the active region require a larger bias voltage and emit at shorter wavelength; the emission wavelength is 3.05μm at T≈80K. The lasers operate up to T≈150K and electroluminescence persists up to room temperature, where the peak position is close to 3.3μm. The short-wavelength limit of such lasers is evaluated based on the dependence of their maximum operation temperatures and on the probable energies of the indirect valleys in the active region.

We demonstrate the design and implementation of a broad-gain and low-threshold (Jth=860A∕cm2 at 8K) quantum-cascade laser emitting between 3.7 and 4.2μm. The active region design is based on strain-compensated In0.73Ga0.27As–AlAs on InP. Laser operation in pulsed mode is achieved up to a temperature of 330K with maximum single-facet output peak powers of 6W at 8K and 240mW at 296K. The temperature coefficient T0 is 119K.

The authors describe the design and implementation of a short-wavelength quantum-cascade laser emitting at approximately 3.3μm at 80K. The active region is based on the strain-compensated In0.73Ga0.27As–In0.55Al0.45As–AlAs heterosystem on InP. The band structure and the strain are controlled through the use of both composite barriers as well as composite wells. The structure is designed so the transition resulting in laser emission is very spatially diagonal; the upper laser state is primarily located in a thick In0.55Al0.45As layer in the injector while the lower laser state is in an In0.73Ga0.27As well. This design allows the lasing transition to bypass (in energy–growth-coordinate space) the lowest indirect X and L valleys of In0.73Ga0.27As, and population inversion is achieved in spite of the upper laser state reaching the energy of the indirect X- and L-valley edges of the adjacent In0.73Ga0.27As well.

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