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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI
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Rezumat: Random substitutional alloys have no long range order (LRO) or translational symmetry so rigorously speaking they have no E(k) band structure or manifestations thereof. Yet, many experiments on alloys are interpreted using the language of band theory, for example by inferring van Hove singularities, band dispersion and effective masses.
While many standard alloy theories have the LRO imposed on the alloy Hamiltonian, assuming only on-site disorder, we have proposed a different way, by using large (thousands of atoms) randomly generated supercells in which chemically identical atoms are allowed to have different local environments (a polymorphous representation). This then drives site-dependent atomic relaxation as well as potential fluctuations. The eigenstates from such supercells are mapped onto the Brillouin zone (BZ) of the primitive cell, producing an effective band structure (EBS).
Our method is presented here to a certain detail and applied to study the effect of gradually increasing the LRO in partially ordered (001) (In,Ga)X (X = P and As) alloys. The results show that (In,Ga)P alloys exhibit band-like behaviour only near the centre and faces of the BZ, rapidly losing such characteristics away from or for higher bands. This system further appears to respond much stronger to changes in its morphology. In contrast, (In,Ga)As shows characteristics of an effective medium alloy in which variations of the LRO has a rather small influence on its EBS.
Keywords: Semiconductor compounds; electronic structure; pseudopotential methods; partial order |
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