Nonlinear Spectroscopy in SemiconductorsFröhlich, D.
doi: 10.1002/(SICI)1521-3951(199909)215:1<7::AID-PSSB7>3.0.CO;2-3pmid: N/A
Due to the additional degrees of freedom in nonlinear spectroscopy as compared to linear spectroscopy, there are much more experiments possible which yield additional information on the electronic parameters of solids. From the consideration of spatial symmetry operators, polarization selection rules are derived which can be connected with wave‐vector conservation to do k‐space spectroscopy. For magnetic materials the introduction of the time‐inversion operator is very useful to be considered together with spatial symmetry operators. One then deals with the magnetic point groups (122 point groups) which, as in the nonmagnetic case (32 point groups), lead to a very systematic study of nonlinear optical properties. It turns out that additional information can be drawn from measuring the phase of nonlinear optical susceptibilities, since for some tensor components there is a phase change connected with applying the time‐inversion operator. The study of the additional degree of freedom of phase change together with the detailed polarization dependence can be used to determine the magnetic structure.
Dielectric Function of Polycrystalline SiC from 190 nm to 15 μmZollner, S.; Liu, Ran; Konkar, A.; Gutt, J.; Wilson, S. R.; Tiwald, T. I.; Woollam, J. A.; Hilfiker, J. N.
doi: 10.1002/(SICI)1521-3951(199909)215:1<21::AID-PSSB21>3.0.CO;2-Opmid: N/A
We have studied polycrystalline SiC using spectroscopic ellipsometry (from the mid‐IR to the quartz‐UV), X‐ray diffraction, and Raman scattering. In the UV, the pseudodielectric function is affected by surface roughness, and the E1 peak is broadened due to the finite grain size. X‐ray rocking curves indicate a preferred orientation with the hexagonal axis along the surface normal and a mosaic spread of 3.5°. FTIR ellipsometry shows a reststrahlen band due to phonon absorption and a strong anistropy peak near the zero crossing of the extraordinary dielectric function at its LO energy. The Raman phonon energies agree with the FTIR results. The Raman data also show the effects of finite grain size and stacking disorder. We conclude that the poly‐SiC wafer is anisotropic, but does not have a well‐defined polytype (such as 6H or 4H).
Modeling the Optical Constants of Diamond‐ and Zincblende‐Type Semiconductors: Discrete and Continuum Exciton Effects at E0 and E1Pollak, F. H.; Muñoz, M.; Holden, T.; Wei, K.; Asnin, V. M.
doi: 10.1002/(SICI)1521-3951(199909)215:1<33::AID-PSSB33>3.0.CO;2-Apmid: N/A
We present a comprehensive model dielectric function ε(E) [= ε1 + iε2] for diamond‐ and zincblende‐type semiconductors based on the energy‐band structure near critical points (CPs) plus discrete as well as continuum excitonic effects at the E0, E0 + Δ0,, E1, and E1 + Δ1 CPs. In addition to the energies of these band‐to‐band CPs, our analysis also yields information about the binding energies of not only the 3D exciton associated with E0 (R0), when resolved, but also the 2D exciton related to the E1, E1 + Δ1 CPs (R1). This model has been applied to spectral ellipsometry measurements of ε1, ε2 (0.3 eV < E < 5.5 eV) of ZnCdSe/InP, CdTe1—xSx, In0.66Ga0.34As, and GaSb and a surface photovoltage spectroscopy determination of the absorption coefficient of GaAs near E0. This work shows conclusively that even if the exciton at E0 is not resolved the lineshape is continuum exciton. The obtained values of R1 exhibit a trend which is in good agreement with effective mass/k · p theory. Our analysis will be compared with the modeling of Adachi and the University of Illinois‐Chicago group, both of whom neglect exciton continuum effects and hence have not evaluated R1. Our results, particularly for exciton continuum effects at E1, have considerable implications for recent first‐principles band structure calculations which include exciton effects.
Optical Spectroscopic Studies of N‐Related Bands in Ga(N, As)Grüning, H.; Chen, L.; Hartmann, Th.; Klar, P. J.; Heimbrodt, W.; Höhnsdorf, F.; Koch, J.; Stolz, W.
doi: 10.1002/(SICI)1521-3951(199909)215:1<39::AID-PSSB39>3.0.CO;2-Bpmid: N/A
We have investigated the unusual band formation at the Γ‐point and in the vicinity of the L‐point in the alloy system Ga(N, As) by various spectroscopic methods. A series of GaNxAs1—x epitaxial layers with x varying from 0.05 to 2.8% was grown on (100) GaAs by metal‐organic vapour phase epitaxy. The samples were studied by photoluminescence (PL) as well as photoluminescence excitation (PLE) spectroscopy, photomodulated reflectance (PR), and conventional reflectance (R) spectroscopy at room temperature and liquid helium temperature. The low‐temperature PL and PLE spectra in the spectral region of the E0 band gap show clear evidence for in‐gap nitrogen‐pair and cluster states at low concentrations (x < 0.1%), and for higher nitrogen concentrations the formation of a new band. The dependence of the E0 band gap on N‐content for x < 1% at 8 K is considerably stronger than at 300 K. Furthermore, R spectra of the E1 and E1 + Δ1 transitions show an uncommonly strong disorder‐induced broadening with increasing N‐content.
Temporally and Spatially Resolved Spectroscopy of GaNKorona, K. P.; Kuhl, J.; Baranowski, J. M.
doi: 10.1002/(SICI)1521-3951(199909)215:1<53::AID-PSSB53>3.0.CO;2-6pmid: N/A
We report temporally and spatially resolved photoluminescence (PL) measurements on a high‐quality single crystal GaN film grown on GaN substrates by metalorganic chemical vapour deposition (MOCVD). The PL decay times for the free A‐excitons and the donor‐bound excitons obtained under low excitation density (100 W/cm2) at liquid helium temperature were about 60 and 250 ps, respectively. Measurements of the PL under higher excitation densities (up to 9 kW/cm2) show that the recombination rates of both free and bound excitons are slower, this observation can be explained by detrapping of donor bound excitons. In spatially resolved measurements, a slight time delay of the free exciton photoluminescence for distant points has been observed. Numerical modeling shows that this delay can be explained by an exciton‐polariton transport with a diffusion constant of approximately 100 cm2/s.