摘要:

Conduction processes in some amorphous semiconductors are reviewed, particularly with a view to understanding the nature of states in the gap due to point defects. Band‐edge localized states extending over from 0.1 to 0.2 eV are thought to exist for glow discharge‐deposited silicon and probably for holes in As2Te3; holes certainly form polarons in SiO2and the possibility exists for chalcogenides. For electrons in SiO2and perhaps many other glasses the range of band‐edge localized states is too small to be observable. The nature of deep states due to defects is contrasted for Si and Ge on the one hand and chalcogenides on the other. For the latter, but not the former, there is a large Stokes shift for such centres. Point defects are proposed as determining drift mobilities, recombination and photoluminescence. The evidence that they are charged is reviewed, as is their possible role in field effect experiments.

ISSN:0094-243X    

DOI:10.1063/1.30754

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The Hubbard model is applied to localized states in the gap of amorphous semiconductors. Two possibilities are considered, depending on whether the effective intrasite correlation energy,U, is repulsive or attractive. For repulsive interactions,U≳0, the Fermi energy behaves normally, positioned halfway between the highest filled and lowest empty quasi‐particle state atT=0. There is a tendency towardsn‐type conduction, variable‐range hopping at low temperatures, and localized spins. On the other hand, when the interaction is attractive, the Fermi energy liesbelowthe energy of the highest filled quasi‐particle state, even atT=0. This effect favorsp‐type conduction, and tends to suppress the appearance of variable‐range hopping. The Fermi energy is strongly pinned in a region in which the density of quasi‐particle states can be small, and no localized spins are present. The experimental results suggest that the tetrahedral amorphous semiconductors have a net repulsive interaction while chalcogenide glasses possess an effect attraction between localized electrons.

ISSN:0094-243X    

DOI:10.1063/1.30739

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Optically induced ESR and absorption due to localized paramagnetic states have been observed in several semiconducting chalcogenide glasses and in amorphous As forT<80K. In the arsenic‐containing chalcogenide glasses and density of these metastble paramagnetic centers is correlated with the estimated density of radiative recombination centers. In GeSe2the absence of this correlation as well as differences in the optically induced ESR spectrum are probably related to differences in the local structural order in GeSe2relative to that of the arsenic chalcogenides.

ISSN:0094-243X    

DOI:10.1063/1.30747

出版商:AIP    

年代:1976

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.30760

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

We identify the unique characteristics of amorphous lone‐pair semiconductors. We support our previous contention of the importance of holes in excited lone‐pair configurations and show by experiment that extrinsic properties can be introduced in intrinsic lone‐pair materials by affecting the charge distribution of localized states in the gap.

ISSN:0094-243X    

DOI:10.1063/1.30774

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A model is presented for recombination in amorphous silicon, the essentials of which are: The fundamental electronic excitation with the lowest energy consists of a trapped electron bound to a trapped hole by Coulombic attraction. This concept is supported by the observation that an electric field in the range of 107Vm−1is able to quench photoluminescence, and by other luminescence and photoconductivity results.

ISSN:0094-243X    

DOI:10.1063/1.30783

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The theory of the eigenvalue spectrum of a system consisting of a Hamiltonian with a random part H and a non‐random term H0is considered. The random part consists of matrix elements which are distributed independently of one another with a Gaussian distribution, but the non‐random part is quite general. An information theoretic argument is used to derive the joint distribution of eigenvalues and a sufficient conduction for a localization is obtained. Essentially this is that the spacing of nearest neighbor eigenvalues in the two matrices should be equal. Attention is drawn to similar phenomena in nuclear physics and it is suggested that such an Anderson‐Mott transition may in fact occur in these systems.

ISSN:0094-243X    

DOI:10.1063/1.30787

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Trends in x‐ray photoelectron (XPS) spectra of chalcogens which relate to their bonding are discussed. Valence band spectra of disordered S are reported along with measurements in the same apparatus of amorphous Se and Te. Each chalcogen’s spectrum has a minimum about 7 eV belowEF, between the largelyp‐derived states nearerEFand thes‐derived states. Thepstates are split into a largely non‐bonding level nearEFand a bonding peak an energy &Dgr;Epbelow it. The splitting &Dgr;Ep(S, 3.5 eV; Se, 2.9 eV; Te, 2.2 eV) grows with decreasing atomic number, Z, and is found to scale with Pauling’s bond energies. Thesstates exhibit an apparent bonding‐antibonding splitting which also grows with decreasing Z and scales with the increasing overlap of thesorbitals. Although thesstates overlap, comparisons with calculated valence levels in the free atom suggest that most of cohesive energy in the chalcogens is gained by the bonding of thepelectrons, with no major contribution from theselectrons.

ISSN:0094-243X    

DOI:10.1063/1.30788

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The effects of fluctuations in both intra‐ and inter‐atomic matrix elements on the spectra of the ’’two‐band’’ tight‐binding models of Weaire and coworkers1are studied using a self‐consistent Green’s function technique. The calculated spectra show the expected broadening of the delta‐function peaks, as well as finite state densities extending above and below each band. The self‐consistent approximation developed can also take account of short‐range order in the fluctuations of interaction energies.

ISSN:0094-243X    

DOI:10.1063/1.30789

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Eight currently available model coordinates for amorphous Ge have been studied. The calculated electronic density of states of these models are compared. Special characteristics of the individual models will be pointed out. Effects of the presence of dangling bonds, surface states and the method of reducing them will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.30790

出版商:AIP    

年代:1976

数据来源: AIP