FINITE-ELEMENT ANALYSIS OF STRAIN EFFECTS ON ELECTRONIC AND TRANSPORT-PROPERTIES IN QUANTUM DOTS AND WIRES

Lattice mismatch in epitaxial layered heterostructures with small char acteristic lengths induces large, spatially nonuniform strains. The co mponents of the strain tensor have been shown experimentally to affect the electronic properties of semiconductor structures. Here, a techni que is presented for calculating the influence of strain on electronic properties. First, the linear elastic strain in a quantum dot or wire is determined by a finite element calculation. A strain-induced poten tial field that shifts and couples the valence subbands in the structu re is then determined from deformation potential theory. The time-inde pendent Schrodinger equation, including the nonuniform strain-induced potential and a potential due to the heterostructure layers, is then s olved, also by means of the finite element method. The solution consis ts of the wave functions and energies of states confined to the active region of the structure; these are the features which govern the elec tronic and transport properties of devices. As examples, two SixGe1-x submicron resonant tunneling devices, a quantum wire with two-dimensio nal confinement and a quantum dot with three-dimensional confinement, are analyzed. Experimentally measured resonant tunneling current peaks corresponding to the valence subbands in the material are modeled by generating densities of confined states in the structures. Size and co mposition-dependent strain effects are examined for both devices. In b oth the quantum dot and the quantum wire, the strain effects on the wa ve functions and energies of confined states are evident in the calcul ated densities of confined states in the structures, which are found t o be consistent with experimentally measured tunneling current/voltage curves for resonant tunneling diodes. (C) 1998 American Institute of Physics. [S0021-8979(98)06419-6]