Excitonic versus plasma screening in highly excited gallium arsenide

We report band edge absorption spectra of GaAs under conditions of high electron-hole pair excitation in the range of 10¹³-10¹⁷ cm^-3 achieved with picosecond light pulses tuned (i) to the 1s exciton energy and (ii) to the continuum (ω#62;E_g), where critical densities for bleaching of the exciton absorption lines are much lower. A substantial blue shift of the 2s absorption line relative to the 1s exciton was found, the latter remained constant in energy up to complete bleaching.     

Many-quantum absorption in gallium phosphide

A study has been made of photoconductivity in GaP induced by 1.78 and 1.17 eV photons from Q-switched ruby or neodymium lasers. Many-quantum processes were observed with 2 to 7 photons participating simultaneously. Double-photon absorption with a phonon participating has also been investigated. The observed many-quantum transitions confirm the recent ideas about GaP zone structure.Based on a generating function method, the theory of many-quantum transitions is developed which takes into account the peculiarities of crystal zone structure. The experimental data are in satisfactory agreement with the theory.Both the many-quantum theory and the experimental method reported in the present paper permit one to study the zone structure of various crystals and to obtain new or supplementary information on fundamental optical constants of solids.     

Magneto-optical transitions in gallium phosphide

The structure of the magnetic levels of the GaP valence band has been calculated within the framework of the effective-mass method. We have determined the effective masses of holes in the direction of a fieldH[001], the probabilities of magneto-optical transitions, and their dependence on the reduced wave vector. The distinctive features of the magneto-optical spectra of GaP are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 66–70, July, 1987.     

Time decay of optically injected free carriers in highly excited GaAs

The time decay of large densities of optically injected free carriers in epitaxial GaAs has been obtained from time-resolved mm wave reflectivity at 300°K. The decay time increases from 5 to 200 nsec as the epitaxial layer thickness increases from 1 to 72 μm, but is independent of injection level (Δn ～ 10¹⁶to 10¹⁸cm_?3) and doping level (norp ～ 10¹⁴to 10¹⁶cm^?3).     

Surface states on gallium phosphide

Ultraviolet photoelectron spectroscopy shows that the surface Fermi level of clean cleaved GaP (10) is pinned 1.50 eV above the valence band maximum of empty surface states. Synchrotron radiation-excited photo-emission partial yield spectroscopy supports this conclusion.     

Heat treatment of gallium phosphide

Annealing effect of GaP depends on the phosphorus pressure observed by Hall effect, X-ray diffraction and photoluminescence. The phosphorus pressure for the peaks of the lattice constant after annealing coincide with that for the high resistivity in the Hall measurement.     

Acceptor excited states in indium phosphide

Selective donon-acceptor pair luminescence and luminescence excitation spectra reveal acceptor excitations to all excited states of principal quantum number 2, odd as well as even parity. These transition energies are independent of the D-A pair separation R for sufficiently large R and are then identical to those on isolated acceptors. However, they decrease significantly at small R and some splittings are revealed in our measurements on a bulk grown crystal in which the most common contaminant acceptor Zn is dominant. The p state transition energies are used together with the known ionization energy of the Zn acceptor to derive valence band parameters for InP according to the theory of Baldereschi and Lipari. We find γ₁ = 5.6 ± 0.7, γ₂ = 2.0 ± 0.3, γ₃ = 2.4 ± 0.3, where γ₁ is adjusted to fit the cyclotron resonance data of Leotin et al. Some reservations concerning the completeness of this theory are acknowledge. Information on the s acceptor excited state is consistent with that obtained from acceptor bound exciton “two-hole” satellites for this remarkable quality bulk crystal.     

Minority carrier lifetime in p-type gallium phosphide

The decay time of the luminescence involving bound minority carriers shortens above some temperature with increasing temperature owing to thermal quenching. However, above some higher temperature there will be a plateau since the luminescence decay cannot be faster than the decay of the excited free minority carriers.     

Triplet bound excitons in copper-doped gallium phosphide

This review describes a particular class of neutral defect complexes in GaP, represented by the variety of Cu-related centres, which are observed to bind excitons in a spin-like singlet-triplet configuration. The reasons for this are discussed and two subgroups are defined. One of these consists of centres which bind holes in localized orbitally nondegenerate spin states, but give rise to highly structured optical spectra. The other group is characterized by featureless photoluminescence spectra in the mid-gap spectral region due to a tight binding of both the electron and hole in spin-like states. Both groups are well described with an essentially identical spin-Hamiltonian formalism, as detailed optically detected magnetic resonance measurements have revealed. The relation of this class of neutral defects in GaP to similar complexes in other semiconductors is discussed.     

Three-photon non-linear cross-section of gallium phosphide

The luminescence of GaP which follows non-linear optical excitation has been studied by using three- and two-photon optical pumping by a neodymium and a ruby laser, respectively. By comparing the intensities of the excitonic A-line emission in the two spectra, the three-photon cross section is obtained. This result is compared with previous experimental and theoretical values.     

Absorption saturation of n-type gallium phosphide

The absorption of n-type gallium phosphide at 2.8 μm wavelength decreases at high light intensity. The saturation intensity is found to be 10 MW cm^?2.     

Second-harmonic generation in strongly scattering porous gallium phosphide

Second-harmonic generation in a strongly scattering macroporous GaP layer with typical sizes of GaP nanocrystals ranging from 200 to 500 nm is studied using nanosecond pulses of an optical parametric oscillator. As the pump wavelength decreases from 1.6 to 1.0 m the second-harmonic yield from porous GaP increases more than one order of magnitude relative to the second-harmonic yield from crystalline GaP. This enhancement of the second-harmonic generation for shorter wavelengths correlates with the increase in the efficiency of light scattering, indicating the importance of scattering effects in nonlinear-optical processes in strongly scattering random media . PACS 42.25.Fx; 42.65.Ky