Fourier transform infrared spectroscopy of III-V compound semiconductors
Abstract
The 3d-transition metal impurities (Mn, Co, and Cu) incorporated into III-V zinc-blende hosts (GaAs, GaP, or InP) exhibit well resolved excitation lines followed by a photoionization continuum in their infrared absorption spectra. They are as sociated with transitions from a “1s-like” ground state to various “p-like” excited states characteristic of a hole bound to a Coulomb center. Their spacings agree remarkably well with those predicted in the effective mass theory for single acceptors (A. Baldereschi and N. O. Lipari, Phys. Rev. B 9, 1525 (1974)) as expected for 3d-transition metal ions substitutionally replacing the group III cations of the host. The shape of the photoionization spectra: the occurrence of the simultaneous excitation of the Lyman transitions in combination with the zone center longitudinal optical (LO) phonon and hence lying in the photoionization continuum and displaying Fano-like asymmetries; the additional continuum excitations to and beyond the p1/2 valence band maximum; …, all these features are described and interpreted. Cu acceptors in GaAs show Lyman doublets, indicative of two independent centers; it is speculated that they could arise from He-like 3d104 s24p1, Cu2− , and H-like 3d94s 24p1, Cu−, Coulomb centers. The infrared transmission spectrum of Si doped MBE-grown GaAs epilayers, 2–2.5 μm thick, measured in the oblique (Berreman) geometry, revealed distinct minima in p-polarization. Given epilayer thickness << reststrahlen wavelength, the minima are identified as the zone center transverse optic phonon (ωTO) and the high frequency LO phonon-plasmon coupled mode (ω+). Analysis of the experimental data yielded free carrier concentrations, ranging from 2.5 × 1017 to 1.4 × 1018 cm−3. The same technique with MBE-grown Si doped In0.53Ga0.47As epilayers (0.5 to 1 μm thick) yielded ω+ modes corresponding to free carrier concentrations 8.2 × 1016 to 2.7 × 10 19 cm−3. The observations of the transmission minima in the Berreman geometry and their interpretation demonstrate a direct and simple method for deducing free carrier concentrations over a wide range.
Degree
Ph.D.
Advisors
Ramdas, Purdue University.
Subject Area
Condensation
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