Theoretical nnaalysis on control of polarization field in GaN-based quantum dot structures and improvement of lasing performance

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We have calculated electronic states of GaN quantum dots (QDs) in AIN using a polarization-potential-dependent sp^3 tight-binding method. We used a Keating-type Valence-Force-Field method for the strain distribution, and a finite-difference method for potential and electric field induced by polarization. The spontaneous and piezoelectric components of polarization are included in the present calculation. We examined a truncated-pyramidal GAN QDs with the base diameter 10.14 nm and the height 2.07nm. This dot size corresponds to that grown in our experiments. It is found that the strong electric field (max.7.14MV/cm) is induced in the QDs due to the polarization. The ground transition energy is calculated to be 3.653 eV which lies in the photon energy rage of the photoluminescence. Owing to the strong electric field, the electron wave function is pushed up toward the top, and the hole wave function is pushed down toward the bottom of the QD. The overlap between the electron and hole wave functions is decreased, and thereby the electron-hole recombination rate is reduced. (the squared overlap is 7.97x10^<-2>.) we developed programs of a l-band effective-mass model and a 8-band k・p model in order to calculate electronic states of QDs with larger sizes. Using these programs, we calculated electronic states in vertically stacked InAs QDs. Here the elastic continuum model is used for the strain distribution. We found a weak coupling between the electronic states in the stacked QDs with the dot spacing 6nm. The programs can be used for calculating electronic states in stacked GaN QDs.