Pressure behaviour of self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots with multi-modal distribution in size

The pressure behaviour of In0.55Al0.45As/Al0.5Ga0.5As self-assembled quantu m dots (QDs) has been studied at 15 K in the pressure range of 0-1.3 GPa. T he atomic force microscopy image shows that the QDs have a multi-modal dist ribution in size. Three emission peaks were observed in the photoluminescen ce (PL) spectra, corresponding to the different QD families. The measured p ressure coefficients are 82, 93 and 98 meV GPa(-1) for QDs with average lat eral size of 26, 52 and 62 nm, respectively. The pressure coefficient of sm all QDs is about 17% smaller than that of bulk In0.55Al0.45As An envelope-f unction calculation was used to analyse the effect of pressure-induced chan ge of barrier height, effective mass and dot size on the pressure coefficie nts of QDs. The Gamma-X state mixing was also included in the evaluation of the reduction of the pressure coefficients. The results indicate that both the pressure-induced increase of effective mass and Gamma-X mixing respond to the decrease of pressure coefficients, and the Gamma-X mixing is more i mportant for small dots. The calculated Gamma-X interaction potentials are 15 and 10 meV for QDs with lateral size of 26 and 52 nm, respectively. A ty pe-II alignment for the X conduction band is suggested according to the pre ssure dependence of the PL intensities. The valence-band offset was then es timated as 0.15 +/- 0.02.