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Nanostructure model and optical properties of InAs/GaAs quantum dot in vertical cavity surface emitting lasers

Chen J., Fan W. J., Ding Y., Xu Q., Zhang X. W., Xu D. W., Yoon S. F., Zhang D. H.

Opto-Electronics Review

2011

Vol. 19, No. 4

449-453

We apply 8.band k.p model to study InAs/GaAs quantum dots (QDs). The strain was calculated using the valence force field (VFF) model which includes the four nearest.neighbour interactions. For the optical properties, we take into account both homogeneous and non.homogeneous broadening for the optical spectrum. Our simulation result is in good agreement with the experimental micro.photoluminescence (µm-PL) result which is from InAs/GaAs QD vertical cavity surface emitting lasers (VCSELs) structure wafer at room temperature. Accordingly, our simulation model is used to predict the QD emission from this QD.VCSELs structure wafer at different temperature ranging from 200–400 K. The simulation results show a decrease of 41 meV of QDground state (GS) transition energy from 250–350 K. The changes ofQDGS transition energy with different temperature indicate the possible detuning range for 1.3.µm wave band QD-VCSELs applications without temperature control. Furthermore, QD differential gain at 300 K is computed based on this model, which will be useful for predicting the intrinsic modulation characteristics of QD-VCSELs.

Spatial separation of recombining carriers within nitride GaN/(AlGa)N quantum wells induced by piezoelectric phenomena

Galczak J., Sarzała R. P., Nakwaski W.

Opto-Electronics Review

2004

Vol. 12, No. 4

369-376

Nitride A III N materials manifest very strong piezoelectric effects. Their piezoelectric coefficients are one order of magnitude higher than those in similar A III B V semiconductors. Therefore stress fields, generated for example at nitride heterojunctions, because of different lattice constants of their both components, are followed by an additional piezoelectric polarization and some local curving of band edges. In quantum wells (QWs), on the other hand, this stress-related piezoelectric polarization and, additionally, the spontaneous polarization are sources of an electric field which causes the so-called quantum confined Stark effect, leading to an effective band-gap shrinkage and spatial separation of electrons and holes. Both the above phenomena influence considerably recombination processes in QW devices. The last effect, i.e. the stress-induced spatial separation of electrons and holes confined within nitride QWs, is investigated theoretically in the present paper. Electron transitions from its ground state to the second heavy-hole state have been found to play much more considerable role in recombination phenomena within wider nitride QWs than it has been expected.