摘要:

The chemical pseudopotential method is used to describe the valence bands of crystalline and amorphous tetrahedral semiconductors; results for silicon crystalline polytypes are similar to those of plane wave methods. Amorphous conduction band states can be described by plane waves orthogonalised to the valence band. The method allows direct calculations of the energy change associated with changes in bond lengths or angles in a distorted network.

ISSN:0094-243X    

DOI:10.1063/1.2945948

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The extended Hu¨ckel Theory has been used to calculate the electronic density of states of tetrahedrally bonded crystalline and amorphous semiconductors. The usefulness of the method for this purpose is critically examined. Intrinsic difficulties in the cluster approach are summarized and programs undertaken to overcome these are sketched.

ISSN:0094-243X    

DOI:10.1063/1.2945949

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The ST12 structure, which contains 5‐atom rings, has been shown to be a fairly satisfactory model for amorphous Ge and Si. This model gives a radial distribution function, electronic density of states, and optical properties in reasonable agreement with experiment. Recently, we have shown that a simple modification of the wurtzite structure, with no 5‐atom rings, also has many similarities to amorphous Ge and Si. Calculation of the photoemission spectrum is a far more detailed test of such models. Electron energy distribution curves (EDC's) have been calculated using the empirical pseudopotential method and an extension of the Gilat‐Raubenheimer method. Comparison with experiment shows the wurtzite and modified wurtzite structures to be unsatisfactory. The ST12 EDC's are in much closer agreement with experiment.

ISSN:0094-243X    

DOI:10.1063/1.2945950

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The equilibrium properties of a single band tight binding model Hamiltonian are calculated within the framework of a generalized quasi‐crystalline approximation. Three particle correlation functions are treated explicitly and the qualitative features of the electronic density of states are found to depend on the form of the short range order in the system. For example, in a close packed solid the spectrum is essentially structureless while in the case of a tetrahedrally coordinated system the density of states exhibits two well defined peaks. The latter statement is in accord with the results of recent cluster calculations and has implications for both the electronic and vibrational spectra of amorphous semiconductors.

ISSN:0094-243X    

DOI:10.1063/1.2945951

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A simple model of the electronic density of states predicts that a p‐band in a cubic solid, ordered or otherwise, has a two‐component structure (of weight two and one) in general. In a tetrahedrally bonded solid the VBDS exhibits upto three components. It is found that the reduction by about 10% of the effective s‐p interaction as a consequence of the bond angle distortion is sufficient to bring about the coalescence of the two lower components.

ISSN:0094-243X    

DOI:10.1063/1.2945952

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We present a new method to study the electronic density of states of an amorphous system of atoms with four‐fold coordination in terms of the local density of states of an atom in a small cluster of this system. Our results show unequivocally that thenumberandtypeof rings of bonds in thevicinity ofandpassing througha certain atom are intimately related to the position and number of peaks in the local density of states of this atom. The method involves choosing a small cluster of atoms and using the Bethe lattice as a boundary condition.

ISSN:0094-243X    

DOI:10.1063/1.2945953

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

For a tight binding Hamiltonian, the moments of the electronic density of states can be simply computed. From these, the density of states is obtained through a continued fraction expression of the Green function. We obtain the local density of states of a continuous random network and on a dangling bond.

ISSN:0094-243X    

DOI:10.1063/1.2945954

出版商:AIP    

年代:1974

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.2945955

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The scattering properties of tetrahedrally bonded amorphous materials are broadly consistent with a random network structure. Evidence obtained by electron microscopy appears to contradict this conclusion, and to favour a microcrystalline structure. The conflict of evidence is not resolved by the discovery that a particular random network model can produce lattice fringes in a computed electron micrograph, since the probability of this occurrence is too low to account for what has been observed in practice. After reviewing recent work on this topic, we conclude that the fringes may be an artefact introduced by insufficient stability of the parameters which determine lens aberrations. Further experimental work is needed.

ISSN:0094-243X    

DOI:10.1063/1.2945956

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We propose a structural model with regions consisting of identical two‐dimensionally perfect layers, stacked randomly on top of one another such that bonds in adjacent layers are in either diamond‐like (staggered) or wurtzite‐like (eclipsed) configurations. The model has perfect tetrahedral coordination everywhere throughout such regions and is consistent with diffraction and other data.

ISSN:0094-243X    

DOI:10.1063/1.2945957

出版商:AIP    

年代:1974

数据来源: AIP