The energy shell structure of a single exciton confined in a self-assembled quantum dot (QD), including excited states, is studied in a regime where the direct Coulomb attraction energy is comparable to the kinetic energy of the carriers. This is achieved via magnetophotoluminescence excitation spectroscopy experiments, where a magnetic field applied perpendicular to the plane of the QD is used to reveal the angular-momentum content of energy shells. The absorption spectrum of the QDs is modeled, and comparison with experiment allows us to relate the observed transitions to interband QD bound-state transitions. The blueshift of the absorption peaks compared to the emission peaks is then interpreted in terms of many-body interactions, and we show that for a highly symmetric situation, the observed energy difference gives a direct measurement of the extra exchange energy gained upon addition of an extra exciton in the QD.

The optical performance of external-cavity lasers based on InAs∕InGaAsP quantum dot laser diodes is investigated. The broad electroluminescence reveals a gain spectrum with full width at half maximum of at least 175nm. By fabricating as-cleaved ridge lasers of different length and width, tuning ranges as high as 110nm have been achieved at wavelengths encompassing 1.55μm. The tuning ranges and efficiencies obtained are limited by internal losses and competition between the external-cavity lasing modes and the laser diode natural lasing modes. The laser diode length is found to affect both the wavelength tuning range and the threshold current density, which is consistent with a quantum-dot type density of states.

We have studied the tuning behavior of an external cavity laser in Littrow configuration using antireflection/high-reflection coated InAs∕InGaAsP∕InP quantum dot laser diodes as the amplifying element. Adding the coatings improves the performance of the setup, and the tunability of the external cavity laser output has been increased up to 166nm. Detailed investigations have revealed that laser diode length and width influence the magnitude of the tuning range. Furthermore, the external differential quantum efficiency is systematically increasing as the external cavity laser wavelength is decreasing. These characteristics are discussed in terms of energy levels available in the inhomogeneous broadening of the self-assembled quantum dots.