Electron minibands, density of states, and absorption fingerprints in tensile-strained Si/relaxed Si1-xGex quantum-dot superlattices

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Résumé

Intermediate-band solar cells require an intermediate electronic manifold that is both confined and sufficiently dispersive to enable sub-bandgap transitions. Here we study a three-dimensional quantum-dot superlattice based on tensile-strained dots embedded in a relaxed ​ matrix, selected to provide electron confinement through the conduction-band offset. We solve a single-band BenDaniel-Duke effective-mass Schrödinger equation using a 3D finite-difference discretization with Bloch boundary conditions, and compute electron miniband dispersions across the Brillouin zone. Energies are referenced to the conduction-band edge of the strained-Si dot, set to zero. We analyze the first three electron minibands as functions of dot size , barrier thickness , and Ge fraction (restricted to within the adopted empirical parameterization). The results show that primarily shifts the miniband bottoms and increases the number of bound states, whereas governs miniband dispersion: for the lowest miniband, the width decreases by nearly two orders of magnitude when increasing from 1 to 5 nm. Increasing raises the confinement barrier from at to at , stabilizing bound minibands and progressively reducing their k-dispersion. Brillouin-zone integration yields an electron density of states and derived spectral indicators, including a DOS based absorption proxy and a final JDOS×overlap absorption spectrum within an independent-particle treatment. These results provide quantitative design trends for engineering robust bound minibands in strained-/ quantum-dot superlattices.

Mots-clés

Absorption, minibands, density of states, quantum dot, superlattice,