Theoretical analysis of lasing characteristics of stacked lnGaN quantum dot lasers from atomic scale

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We have analyzed the electronic structures of ln_<0.2>Ga_<0.8>N pyramidal quantum dots (QDs) in a GaN barrier layer using a polarization-potential dependent sp^3 tight-binding method. A valence-force-field method using the Keating potential was used for the strain and atom-position calculations. For the QD with the diameter 86.4 A, height of 20.8 A, and facet inclination angle of 30 degree, the maximum piezoelectric field is calculated to be1.64 MV/cm. The energy gap shows a red shift of 0.100 eV due to the quantum-confined Stark effect. The field causes a spatial separation of the electron and hole wave functions in the QD. The number of electron-hole pairs, which can screen the field totally, is estimated as a function of the diameter. We find that 13 electron-hole pairs are required for the complete field screening for the QD with the diameter 86.4 A. In experiments by Damilano et al., the photoluminescence peak energy, E_<PL>, of 2.71 eV (at room temperature) was measured for the MBE-grown In_<0.2>Ga_<0.8>N QDs with the similar QD size ; diameter = 100 A, heitht = 20 A. Eg = 2.706 eV for the pyramidal QD is in better agreement with the measured energy, E_<PL> = 2.71 eV, than Eg = 2.502 eV for the prismatic QD.