An Analytically Tractable Structure Model for Disordered Systems. II. Complicated Structures and Application to Amorphous Selenium

Unger, H.-J.

doi:10.1002/pssb.2220760245

Cited by 8 publications

(1 citation statement)

References 24 publications

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“…Consider the positional disorder in element semiconductors as a-Si and a-Ge (e.g. [34] and other references therein). These materials form continuous random structures interspersed with a relatively large number of imperfections which are principially in the form of larger or smaller voids.…”

Section: Two-band System Of Amorphous Silicon or Germaniummentioning

confidence: 99%

Covalent Bonds in Amorphous Semiconductors and Their Influence on the Structure of the Energy Spectrum

Unger¹

1990

Physica Status Solidi (b)

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The structure of the energy spectrum of amorphous semiconductors as determined by the formation of covalent bonds is analyzed. In contrast with other theoretical models all considerations are based on a realistic model of the atomic structure of a-Si and a-Ge. The mathematical method used throughout the paper is, within certain subspaces (cells) of the total Hilbert space, the partial diagonalization of the Hamiltonian represented in an "extended Hilbert space". Existing model Hamiltonians, e.g. the Weaire-Thorpe model, are generalized in such a way that real disordered solids can be described. The molecular model used in this paper yields the basic feature of the structure of the energy spectrum. For positionally disordered systems an Anderson-like Hamiltonian is obtained. The formation of extended and localized states in disordered solids is explained by taking into account the residual interactions. Conditions for the localization of electronic states and the existence of mobility edges depending on the local and global atomic structure of amorphous semiconductors are given. A generalization of the cell model in the spirit of the scaling theory of localization leads to a method for the determination of the position of the mobility edges. Structural correlation in amorphous semiconductors manifesting itself in short-range order and in the existence of voids, which is not taken into account e.g. in the Anderson model, is found to be the origin of the basic structural properties of the energy spectrum of disordered semiconductors. Conclusions from the theory proposed are in accordance with experimental findings and explain them.

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Section: Two-band System Of Amorphous Silicon or Germaniummentioning

confidence: 99%

Covalent Bonds in Amorphous Semiconductors and Their Influence on the Structure of the Energy Spectrum

Unger¹

1990

Physica Status Solidi (b)

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Structure Model of a One‐Dimensional Disordered System with Short‐Range Order

Unger¹

1977

Annalen der Physik

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Abstract. An ensemble of disordered linear chains is described by a probability density distribution without making use of the laws of thermodynamical equilibrium statistics. Short-range order is present in the system, because the position of an arbitrary particle depends on the location of the nearest neighbours. The nearest neighbour distance statistics is assumed to be of the Gaussian type.All correlation functions are calculated for finite and infinite systems. The superposition approximation is found to hold rigorously. The pair correlation is of fundamental importance for the system. The radial pair distribution function is investigated thoroughly. The configurational entropy of the system is calculated and discussed. Strukturmodell eines eindimensionalen ungeordneten Systems mit NahordnungInhaltsubersicht. Ein Ensemble ungeordneter hearer Ketten wird dureh eine Wahrscheinlichkeitsdichteverteilung beschrieben, ohne dabei die Prinzipien der Gleichgewichtsstatistik zu verwenden. Das System besitzt Nahordnung, u)eil die Position eines beliebigen Teilchens von der Lage seiner nachsten Nachbarn abhlingt. Die Abstandsstatistik nlichster Nachbarn nird durch eine GauBverteilung beschrieben. Alle Korrelationsfunktionen werden fur endliche und unbegrenzte Systeme berechnet. Die exakte Giiltigkeit des Superpositionsgesetzes wird bewiesen. Die Paarkorrelation ist von grundlegender Bedeutung fur das System. Die radiale Paarverteilungsfunktion wird eingehend untersucht. Die Konfigurationsentropie des Systems wird berechnet und diskutiert.

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Molecular Liquid Model and Electronic Structure of Amorphous Silicon and Germanium

Halder¹,

Shenoy²

1980

Physica Status Solidi (b)

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The atomic and electronic structure of amorphous Si and Ge are investigated by the molecular liquid model (MLM). The theoretJical structure factor is calculated using three simple parameters -nearest neighbor distance, packing density, and coordination number. The electronic density of states obtained with the MLM structure factor, and nonlocal energy dependent pseudopotential in second order perturbation theory, show good agreement with experimental and other theoretical results.Die atomare und elektronische Struktur von amorphem Si und Ge wird mit dem Molekulflussig keitsmodell (MLM) untersucht. Der theoretische Strukturfaktor wird mit drei einfachen Parametern -den1 Abstand nachster Nachbarn, der Packungsdichte und der Koordinationszahlberechnet. Die mit dem MLM-Strukturfaktor erhaltene elektrische Zustandsdichte und das mi6 Storungsrechnung zweiter Ordnung bestimmte nichtlokale energieabhangige Pseudopotential zeigen gute ubereinstimmung mit experimentellen und anderen theoretischen Ergebnissen.

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An Analytically Tractable Structure Model for Disordered Systems. II. Complicated Structures and Application to Amorphous Selenium

Cited by 8 publications

References 24 publications

Covalent Bonds in Amorphous Semiconductors and Their Influence on the Structure of the Energy Spectrum

Covalent Bonds in Amorphous Semiconductors and Their Influence on the Structure of the Energy Spectrum

Structure Model of a One‐Dimensional Disordered System with Short‐Range Order

Molecular Liquid Model and Electronic Structure of Amorphous Silicon and Germanium

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