L C D Gonçalves

Theoretical investigation of the photoluminescence and Fermi surface of periodically delta -doped GaAs

A theoretical study of the electronic structure of periodically delta -doped GaAs is presented. When the doping period is reduced, minibands are formed, and the photoluminescence spectrum presents a broad emission band at energies above the GaAs band edge. The experimentally obtained photoluminescence lineshape is well reproduced by the theory. The calculated cut-off energy in the photoluminescence spectrum is in excellent agreement with the experimental value. The Fermi surface is studied as a function of the doping period. The gradual change in the Fermi surface which occurs when the spacing between the dopant sheets decreases, provides a clear-cut description of the crossover from two- to three-dimensional electronic structure in delta -doped GaAs. The response of the system to a magnetic field, applied in the plane of the layers, is considered, and the condition of magnetic breakdown is studied.

Single and periodically Si -doped InP grown by LP-MOVPE

Single and periodically Si -doped InP layers were grown by LP-MOVPE at . A full width at half maximum of 32 ? was obtained for the net charge concentration profile for a sample with a peak net charge concentration of . Numerical simulations showed that the impurities are localized over less than three InP monolayers. No dopant diffusion or segregation was observed. The periodic structures, grown with barriers varying from 100 to 300 ?, all had nearly the same carrier sheet concentration per dopant layer and impurity localization characteristics.

Electronic and optical properties of periodically Si δ-doped InP grown by low pressure metalorganic vapor phase epitaxy

A series of periodically Si δ-doped InP samples with 5 and 10 periods varying from 92 to 278 A has been investigated in terms of the transport and optical properties. A reduction in mobility with decreasing period was observed due to the increasing overlap of the electronic wavefunction with the various Si planes. A broad band emission was detected for the periodic structures at energies higher than the InP band gap. The cutoff energy for this band decreases with the period and this behavior can be described by a d−2/3 decay. The results are discussed and compared with the ones for GaAs available in the literature.

Characterization of -doped superlattices by Shubnikov - de Haas measurements

The Shubnikov - de Haas oscillations of InP with a periodical planar doping with Si were studied at 4.2 K in fields of 0 - 14 T. By confronting the oscillation frequencies detected experimentally with the ones predicted on the basis of the effective-mass approximation the carrier population of the superlattice minibands and the characteristic width of the doped layer were obtained. The width of the doped layer obtained in this way is in good agreement with the value obtained from C - V profiling measurements on the same structures.

High magnetic field transport and photoluminescence in doped InGaAs/InP superlattices

Lattice-matched InP/InxGa1- x As short period superlattices (x = 0.53) d-doped with Si in the middle of the InP barriers were studied. The samples had a high carrier concentration which filled two minibands. In addition to a peak associated with the electrons from the second miniband, E2, the Shubnikov-de Haas spectra showed a well resolved doublet structure that is assigned to E1 electrons of superlattice wave vectors kz = 0 and kz = p /d. From the lineshape of the Shubnikov-de Haas oscillations, an E1 quantum mobility of 970 cm2/Vs was deduced, which represents an increase of about 40% over the value for periodically delta-doped semiconductors. The photoluminescence ex- hibits a band at photon energies higher than the InGaAs bandgap and whose FWHM approximates the Fermi energy of the confined carriers. Thus the photoluminescence observed is consistent with the recombination of electrons confined by the superlattice potential and photoexcited holes.

Electronic properties of gated -doped semiconductors

The quantum and transport subband mobilities as a function of applied bias were calculated for a gated -doped semiconductor. The electronic spectra (envelope wavefunctions, subband energies and Fermi energy) for the structure under bias used as input in the calculations were obtained by either solving self-consistently Schr?dinger and Poisson equations or by solving the Schr?dinger equation with a confining potential determined by the Thomas - Fermi semiclassical approximation. In the first case the screening of the electron-ionized impurity interaction was treated in the random phase approximation, whereas in the latter case the two-dimensional Thomas - Fermi model of screening was used. Results show that although the semiclassical approach offers the advantage of greater simplicity, it describes reliably the carrier mobility in the fundamental subband only. The dependence of the mobility of carriers in individual subbands on applied bias correlates with the evolution with bias of the overlap between subband wavefunctions and the doped-layer region.

Characterization of periodically -doped semiconductors by capacitance - voltage profiling

The capacitance - voltage (C - V) profiles of periodically Si--doped InP samples were measured, and these are described by a succession of equally spaced peaks, with a spatial periodicity which closely matches the intended doping period. Theoretical C - V spectra for periodically Si--doped semiconductors were calculated. Analysis of the data indicates that the spacing between the peaks seen in the experimental C - V spectrum is a reliable measure of the true doping period of the sample. The C - V spectrum of the periodically -doped semiconductor is well approximated by a linear combination of C - V curves for isolated -doped layers located at successive positions of analogous layers in the periodically -doped sample. The practical limitations of the C - V technique when applied to periodically -doped semiconductors are discussed.