Supernonlinear Shifts of Optical Energy Gaps in InSe and GaSe under Hydrostatic Pressure

Absorption spectra are measured in layered semiconductors InSe and GaSe intercalated with lithium and sodium. A non-monotonous shift is found of the free exciton lines for Na,InSe, Na,GaSe, and Li,GaSe when 2 increases: a t specific values of intercalant content the short-wavelength shift changes into the long-wavelength one. Interpretation of the results is made in terms of the strain effects of van der W a d s and intralayer bondings which shift the electronic levels of the semiconductor.Es werden die Absorptionsspektren in den Schichthalbleitern InSe und GaSe gemessen, die mit Lithium und Natrium interkaliert sind. Es wird gefunden, daS sich fiir NaJnSe, Na,GaSe und Li,GaSe die Linie der freien Exzitonen monoton verschiebt, wenn z ansteigt: bei einem spezifischen Wert des Interkalantgehalts andert sich die kurzwellige Verschiebung in eine langwellige. Eine Interpretation der Ergebnisse wird mit Spannungseffekten der van der Waals-und Zwischenschichtbindungen gegeben, die die elektronischen Niveaus des Halbleiters verschieben.

Section: Discussionsupporting

confidence: 54%

Section: Resultsmentioning

confidence: 99%

Alkali‐Metal‐Intercalated Indium and Gallium Selenides Non‐Monotonous Shift of Exciton Lines

Lukyanyuk¹,

Voronyuk²,

Kovalyuk³

1989

“…(1) At low pressures, the band structure calculations reproduce, at least qualitatively, the well-known change in sign [45] from negative to positive of the pressure coefficient of the lowest direct gap of ε -GaSe (labeled E Γ1 in Fig. 5); the sign change is related to a competition between interlayer and intralayer interactions, see Ref.…”

Section: Electronic Structure Of E-gase Under Pressurementioning

confidence: 57%

Effect of pressure on the structural properties and electronic band structure of GaSe

Schwarz

Olguı́n

Cantarero

et al. 2006

The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the ε -GaSe to a disordered NaCl-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered ε -phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga -Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga -Ga and Se -Se bond lengths which were not accessible to a direct experimental determination yet. Based on the optimized structural parameters, we report calculations of band gap changes of ε -GaSe under pressure. The optical response and electronic band structure of the metallic high-pressure phase of GaSe are discussed briefly.

“…First, the electron effective mass is expected to increase at a slower rate than the band gap, as it is basically determined by higher energy direct allowed transitions with lower pressure coefficient [12,13]. Second, the sharp decrease of the slope starting at 3 GPa could be viewed as a signature of direct-indirect conduction band crossover that have been evidenced by intrinsic photoluminescence at room temperature, as electrons in the conduction band minimum at the Brillouin zone edge are expected to have a much higher effective mass [2].…”

Section: Resultsmentioning

confidence: 99%

High pressure and high magnetic field behaviour of free and donor‐bound‐exciton photoluminescence in InSe

Millot

Gilliland

Broto

et al. 2009

We report here first magneto‐photoluminescence investigations under high pressure up to 6 GPa on III–VI layered semiconductor InSe. Both diamagnetism and magnetic field induced gap opening driven by Landau quantization became observable by using a 60 T pulsed magnet. The pressure‐induced enhancement of the diamagnetic coefficient is consistent with the increase of the dielectric constant under pressure while the evolution of the linear coefficient is consistent with a slight increase of the electron effective mass up to 4 GPa and a direct‐to‐indirect conduction‐band crossover around that pressure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)