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Electronic band -edge properties of rock salt PbY and SnY (Y = S, Se, and Te)
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-9050-5445
2008 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 30, no 9, 1451-1460 p.Article in journal (Refereed) Published
Abstract [en]

The electronic band-edges of lead chalcogenides PbY and tin chalcogenides SnY (where Y = S, Se, and Te) are investigated by the means of a full-potential linearized augmented plane wave (FPLAPW) method and the local density approximation (LDA). All six chalcogenide binaries have similar electronic structures and density-of-states, but there are differences in the symmetry of the band-edge states at and near the Brillouin zone L-point. These differences give the characteristic composition, pressure, and temperature dependences of the energy gap in Pb1-xSnxY alloys.We find that: (1) SnY are zero-gap semiconductors E-g = 0 if the spin-orbit (SO) interaction is excluded. The reason for this is that the conduction band (CB) and the valence band (VB) cross along the Q equivalent to LW line. (2) Including the SO interaction splits this crossing and creates a direct gap along the Q-line, thus away from the L symmetry point. Hence, the fundamental band gap E-g in SnY is induced by the SO interaction and the energy gap is rather small Eg approximate to 0.2-0.3 eV. At the L-point, the CB state has symmetric L-4(+) and the VB state is antisymmetric L-4(-) thereby the L-point pressure coefficient partial derivative E-g(L)/partial derivative p is a positive quantity. (3) PbY have a direct band gap at the L-point both when SO coupling is excluded and included. In contrast to SnY, the SO interaction decreases the gap energy in PbY. (4) Including the SO interaction, the LDA yields incorrect symmetries of the band-edge states at the L-point; the CB state has L-4(+) and the VB state has L-4(-) symmetry. However, a small increase of the cell volume corrects this LDA failure, producing an antisymmetric CB state and a symmetric VB state, and thereby also yields the characteristic negative pressure coefficient partial derivative E-g(L)/partial derivative p in agreement with experimental findings. (5) Although PbY and SnY have different band-edge physics at their respective equilibrium lattice constants, the change of the band-edges with respect to cell volume is qualitatively the same for all six chalcogenides. (6) Finally, in the discussion of the symmetry of the band edges, it is important to clearly state the chosen unit cell origin; a shift by (a/2,0,0) changes the labeling L-4(+) double left right arrow L-4(-) of the irreducible representations.

Place, publisher, year, edition, pages
2008. Vol. 30, no 9, 1451-1460 p.
Keyword [en]
electronic structure, lead chalcogenides, tin chalcogenides, infrared detectors materials, band symmetries
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7343DOI: 10.1016/j.optmat.2007.09.001ISI: 000256413100018Scopus ID: 2-s2.0-42649102062OAI: oai:DiVA.org:kth-7343DiVA: diva2:12330
Note
Uppdaterad från submitted till published(20101117) QC 20101117Available from: 2007-06-20 Created: 2007-06-20 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Electronic structure and optical properties of PbY and SnY (Y=S, Se, and Te)
Open this publication in new window or tab >>Electronic structure and optical properties of PbY and SnY (Y=S, Se, and Te)
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Lead chalcogenides and tin chalcogenides and their alloys are IV−VI family semiconductors with unique material properties compared with similar semiconductors. For instance, PbY (Y = S, Se, and Te) are narrow-gap semiconductors with anomalous negative pressure coefficient and positive temperature coefficient. It is known that this behavior is related with the symmetry of wave functions in first Brillouin zone L-point, which moves the edges of valence band maximum and conduction band minimum towards each other with pressure increasing. SnTe has opposite behavior since its wavefunction symmetry is different from PbY. Therefore, by alloying PbTe and SnTe one can change and control the band gap energy and its pressure or temperature dependence. These chalcogenides alloys have therefore a huge potential in industrial low-wavelength applications and have been attracted the attention of researchers.

This thesis comprises theoretical studies of PbY, SnY (Y = S, Se and Te) and the Pb1xSnxTe alloys (x = 0.00, 0.25, 0.50, 0.75, and 1.00) by means of a first-principles calculation, using the full-potential linearized augmented plane waves method and the local density approximation.

The optical properties of Pb1xSnxTe alloys are investigated in terms of the dielectric function ε(ω) = ε1(ω) + 2). We find strong optical response in the 0.5–2.0 eV region arising from optical absorption around the LW-line of the Brillouin zone. The calculated linear optical response functions agree well with measured spectra from ellipsometry spectroscopy performed by the Laboratory of Applied Optics, Linköping University. The calculations of the electronic band-edges of the binary PbY and SnY compounds, show similar electronic structure and density-of-states, but there are differences of the symmetry of the band-edge states at and near the Brillouin zone L-point. PbY have a band gap of Eg 0.15−0.30 eV. However, SnY are zero-gap semiconductors Eg = 0 if the spin-orbit interaction is excluded. The reason for this is that the lowest conduction band and the uppermost valence band cross along the LW line. When including in PbY. Although PbY and SnY have different band-edge physics at their respective equilibrium lattice constants, the change of the band-edges with respect to cell volume is qualitatively the same for all six chalcogenides. The calculations show that the symmetry of band edge at the L-point changes when lattice constant varies and this change affects the pressure coefficient. the spin-orbit interaction a gap Eg ≈ 0.2 eV is created, and hence this gap is induced by the spin-orbit interaction. At the L-point, the conduction-band state is a symmetric state and the valence-band state is antisymmetric thereby the L-point pressure coefficient +4L−4LpEg∂∂/)L( in SnY is a positive quantity. In contrast to SnY, the PbY compounds have a band gap both when spin-orbit coupling is excluded and included; this gap is at the L-point, and the conduction-band state has and the valence-band state has symmetry, and thereby this band edge yields the characteristic negative pressure coefficient +4L−4LpEg∂∂/)L(

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. x, 36 p.
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4444 (URN)978-91-7178-654-8 (ISBN)
Presentation
2007-06-14, K408, KTH, Brinellvägen 23, Stockholm, 14:00
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Note
QC 20101117Available from: 2007-06-20 Created: 2007-06-20 Last updated: 2010-11-17Bibliographically approved

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