Influence of Internal Fields on the Electronic Structure in\n Self-Assembled InAs/GaAs Quantum Dots

Built-in electrostatic fields in Zincblende quantum dots originate mainly\nfrom - (1) the fundamental crystal atomicity and the interfaces between two\ndissimilar materials, (2) the strain relaxation, and (3) the piezoelectric\npolarization. In this paper, using the atomistic NEMO 3-D simulator, we study\nthe origin and nature of the internal fields in InAs/GaAs quantum dots with\nthree different geometries, namely, box, dome, and pyramid. We then calculate\nand delineate the impact of the internal fields in the one-particle electronic\nstates in terms of shift in the conduction band energy states, anisotropy and\nnon-degeneracy in the P level, and formation of mixed excited bound states.\nModels and approaches used in this study are as follow: (1) Valence force field\n(VFF) with strain-dependent Keating potentials for atomistic strain relaxation;\n(2) 20-band nearest-neighbor sp3d5s* tight-binding model for the calculation of\nsingle-particle energy states; and (3) For piezoelectricity, for the first time\nwithin the framework of sp3d5s* tight-binding theory, four different\nrecently-proposed polarization models (linear and non-linear) have been\nconsidered in conjunction with an atomistic 3-D Poisson solver that also takes\ninto account the image charge effects. Specifically, in contrast to recent\nstudies on similar quantum dots, our calculations yield a non-vanishing net\npiezoelectric contribution to the built-in electrostatic field. Demonstrated\nalso is the importance of full three-dimensional (3-D) atomistic material\nrepresentation and the need for using realistically-extended substrate and cap\nlayers (systems containing ~2 million atoms) in the numerical modeling of these\nreduced-dimensional quantum dots.\n