15 research outputs found
Electron-phonon renormalization of the absorption edge of the cuprous halides
Compared to most tetrahedral semiconductors, the temperature dependence of
the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small.
CuCl and CuBr show a small increase of the gap with increasing
temperature, with a change in the slope of vs. at around 150 K: above
this temperature, the variation of with becomes even smaller. This
unusual behavior has been clarified for CuCl by measurements of the low
temperature gap vs. the isotopic masses of both constituents, yielding an
anomalous negative shift with increasing copper mass. Here we report the
isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of
CuI. The measured isotope effects allow us to understand the corresponding
temperature dependences, which we also report, to our knowledge for the first
time, in the case of CuI. These results enable us to develop a more
quantitative understanding of the phenomena mentioned for the three halides,
and to interpret other anomalies reported for the temperature dependence of the
absorption gap in copper and silver chalcogenides; similarities to the behavior
observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
Isotope effects on the electronic critical points of germanium: Ellipsometric investigation of the E
Within the past years the optical excitations of electrons
have been measured for semiconductor samples of different
isotope compositions. The isotope shift observed
have been compared with calculations of the effects of
electron-phonon interaction on the electronic band structure.
While qualitative agreement has been obtained, some
discrepancies remain especially concerning the
E1 and transitions.
We have remeasured the effect of isotope mass on the
E1 and transitions of
germanium with several isotopic compositions.
The results, obtained by means of spectroscopic
ellipsometry, confirm that the real part of the gap
self-energies induced by electron-phonon interaction is
larger than found from band structure calculations,
while the imaginary part agrees with those
calculations, which are based on a pseudopotential band structure and
a bond charge model for the lattice dynamics. Our results agree
with predictions based on the measured temperature
dependence of the gaps. We compare our data for
E1 and with
results for the lowest direct (E0) and indirect
(Eg) gaps. The measured values of
and increase noticeably with increasing
isotope mass. Similar effects have been observed in the
temperature dependence of in
and . A microscopic explanation for this effect
is not available
Isotope effects on the electronic critical points of germanium: ellipsometric investigation of the E1 and E1+δ1 transitions.
Comment on "Ab initio calculation of excitonic effects in the optical spectra of semiconductors".
Determination of the piezo-optical properties of semiconductors above the fundamental gap by means of reflectance difference spectroscopy.
Piezo-optical properties of ZnSe and ZnTe above the fundamental gap studied by reflectance difference spectroscopy.
Measurement of the Surface Strain Induced by Reconstructed Surfaces of GaAs (001) Using Photoreflectance and Reflectance-Difference Spectroscopies
Optical anisotropy of (001)-GaAs surface quantum wells
We report a reflectance difference spectroscopy (RDS) study of
the optical anisotropy of GaAs:(001) Surface quantum wells
consisting of a thin GaAs layer (3-30 nm thick) embedded
between an arsenic reconstructed surface and an AlAs barrier.
The RDS spectra display anisotropic contributions from the free
Surface and from the GaAs/AlAs interface. By comparing RDS
spectra for the c(4x4) and (2x4) Surface reconstructions, we
separate these two contributions, and demonstrate that the
anisotropy around the E-1 and E-1 + Delta(1) transitions
comprises a component originating from modifications of bulk
states near the surface. The latter is attributed to
anisotropic strains induced by the surface reconstruction. The
experimental data Lire well described by a model for the RDS
response of the multilayer structures, which also takes into
account the blue energy shifts and the changes in oscillator
strength of the E-1 and E-1 + Delta(1) transitions induced by
quantum-well confinement