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HL: Fachverband Halbleiterphysik

HL 3: Heterostructures

HL 3.8: Vortrag

Montag, 23. März 2009, 12:15–12:30, BEY 154

Tight-binding CPA Theory of Semiconductor Alloys — •Daniel Mourad und Gerd Czycholl — Institut für Theoretische Physik, Universität Bremen

Alloys of the type A_xB_1−x can be realized for a wide class of semiconductor materials, e.g. for Al_xGa_1−xAs, In_xGa_1−xAs, Cd_xZn_1−xSe, Si_xGe_1−x ,Al_xGa_1−xN, Ga_xIn_1−xN, and many others. These substitutional semiconductor alloys find widespread applications in particular in nanoelectronic devices as quantum wells, quantum wires and quantum dots (QDs), as the band gap varies continuously with x, and therefore a band structure tayloring is possible by varying x. To calculate the electronic properties of such semiconductor alloys we start from multiband (sp³) tight-binding (TB) models for the pure bulk semiconductor material A and B and apply the coherent potential approximation (CPA) to calculate the (configurationally averaged) electronic density of states and effective band structure. This treatment allows, in particular, for a reproduction of band bowing effects as a function of the concentration x and leads automatically to finite lifetime effects due to the loss of translational invariance. We compare the CPA results with results obtained in the much simpler virtual crystal approximation (VCA) and with ensemble averaged finite supercell calculations. Additionally, the application to QDs by combining this CPA-TB treatment with the recently developed TB models of nanostructures is hinted.