Recent results on molecular-beam epitaxy growth of the quantum dot InGaAs/GaAs heterostructures for long-wavelength lasers on GaAs substrates are presented. As a result of optimization of the growth procedure for active region and emitter layers low-threshold current density (45 - 80 A/cm2) long-wavelength (1.27 - 1.3 μm) laser diodes may be fabricated with high reproducibility.
Development of submonolayer deposition technique can offer significant flexibility in creation of strained heterostructures of different types and material systems. It was found that under certain growth conditions the deposition of InAs insertions of less than 1 monolayer (ML) thickness in GaAs matrix forms so-called sub-monolayer quantum dots (SML QDs). The energy spectrum of these QDs can be varied over a wide range by tuning the InAs coverage and the thickness of GaAs spacers. Stranski-Krastanow (In,Ga)As QDs (SK QDs), which have been investigated in more details, have proved theoretically predicted lower threshold current density of 26 A/cm2 in compare with QW lasers. However, strong size variation of SK QDs in combination with the relatively low sheet density leads to low peak gain achievable in the ground state. This problem is the reason of typically low efficiency of SK QD-based lasers. Due to higher gain, SML QDs have proved their potential for high power laser application. In this presentation we report on further progress in the technology of SML QD lasers demonstrating high output power (6W) from 100-μm-wide laser diode emitting at 0.94 μm. High power QW-based lasers of the state-of-the-art performance are also presented for comparison.
Optical properties of GaAsN/GaAs heterostructures with different N contents grown by molecular-beam epitaxy were investigated. We show that under the certain grows reigmes the optical properties of the GaAsN layers are determined by recombination via localized states which is due to composition fluctuation. An increase in the N concentration leads to increase in composition fluctuation and, correspondingly, to increase in energy of localized states. Thermal annealing reduces nonuniformity distribution of nitrogen atoms. In short-period GaAsN/GaAs superlattice the effects of phase separation can be enhanced.
Optical and structural properties of self organized InGaAs quantum dots (QD), deposited in Al0.3Ga0.7As matrix, were investigated. Samples were grown by molecular-beam epitaxy (MBE). It is shown, that deposition of 1.7 - 4 monolayer of InAs on Al0.3Ga0.7As surface results in formation of nanoscale QDs on 1 - 2 monolayer thick wetting layer (Stranski-Krastanov growth mode). Large exciton localization energy of the InAs QDs in Al0.3Ga0.7As in compare with QDs in GaAs is demonstrated. This is due to increase in size of these QDs and significant bandgap offset in the case of InAs/AlGaAs system in compare with InAs/GaAs one.