Showing papers on "Photoluminescence published in 1969"

Photoluminescence of Metals

Abstract: Radiative recombination in gold, copper, and gold-copper alloys has been observed arising from transitions between electrons in conduction-band states below the Fermi level and holes in the $d$ bands generated by optical excitation.

Optical Properties of n‐Type GaAs. I. Determination of Hole Diffusion Length from Optical Absorption and Photoluminescence Measurements

Abstract: Hole diffusion lengths L were determined for several Te‐doped GaAs crystals with electron concentrations ranging from 2×1016 to 6.5×1018 cm−3. The values of L were obtained by fitting experimental photoluminescence spectra to a theoretical expression which contains the measured absorption coefficients. This expression was derived from radiative recombination statistics, taking into account the reabsorption of emitted photons and the diffusion of minority carriers. The idea used by van Roosbroeck and Shockley of introducing the measured absorption coefficient by means of the principle of detailed balance is shown here to be valid for both nondegenerate and degenerate n‐type GaAs. It was found that the hole diffusion lengths are nearly independent of electron concentration n for n 2×1018 cm−3 values for diffusion length decrease rapidly with increasing n. This decrease is attributed to the formation of additional defects associated with donor complexes or precipitates, or both. The diffusion lengths determined in this work are in good agreement with those found by Wittry and Kyser from the electron‐beam excitation method but are larger than those obtained by Aukerman et al. from short‐circuit current measurements on n‐type surface barrier diodes subjected to high‐energy electron bombardment.

Photoexcitation and Luminescence in Redox Processes on Gallium Phosphide Electrodes

Abstract: The mechanism of the charge transfer between energy states of electrons in electrodes and redox systems was studied. Measurements of the photoexcitation of electrons in have shown that not only the conduction and valence band but also surface states are involved in the charge transfer at the interface. Electroluminescence is observed if minority carriers are injected into the electrode. The corresponding recombination process is compared with that of the photoluminescence. Quenching effects are discussed.

Photoluminescence in SrTi O 3

Abstract: At 77 K photoluminescence from nominally pure, 0.05% Sm-doped and 0.005% Cr-doped SrTi${\mathrm{O}}_{3}$ gives identical spectra in the infrared (I.R.) with an intensity ratio of 1:20:400, respectively. In undoped and Sm-doped specimens, the intensity of emission is vanishingly weak at 4 K, in contrast to Cr-doped SrTi${\mathrm{O}}_{3}$, in which it is practically unchanged relative to that at 77 K. At 77 K, the spectrum consists of a narrow line at 1.5625 eV of half-width 0.5\ifmmode\times\else\texttimes\fi{}${10}^{3}$ eV, which we identify as the zero-phonon line, and 31 satellite lines, which are shown to be vibronics due to lattice phonons from the center and edge of the Brillouin zone. At 4 K the zero-phonon line is a doublet. Comparison with the reported lattice phonon spectrum is satisfactory. In addition, the data suggest the energies of several zone boundary phonons which have not been reported. In spite of identical emission spectra, undoped, Sm-doped, and Cr-doped specimens have different excitation spectra. This suggests energy transfer from Sm or Cr to a tightly bound center, isolated from the electronic energy bands, such as typically arise from rare-earth ions in ionic crystals. It is suggested that the center is an intrinsic defect or an exciton. In undoped SrTi${\mathrm{O}}_{3}$ an emission band in the visible---2.175 eV (77 K), 2.475 eV (4 K)---and its excitation spectrum are reported. The temperature dependence of both are anomalous. In contrast to the infrared emission, it is broad (half-width 0.63 eV) and structureless. Application of a dc electric field \ensuremath{\sim}100 V/cm, at 4 K, induces oscillations in time of the visible emission, a property not shared by the I.R. emission.

Optical Properties of n‐Type GaAs. II. Formation of Efficient Hole Traps during Annealing in Te‐Doped GaAs

Abstract: The photoluminescence intensity of the near gap emission from Te‐doped GaAs crystals decreases greatly after annealing at temperatures ranging from 600° to 1000°C while at the same time the intensity increases in the 1.22‐eV band. The decrease in the near gap emission is less for samples annealed at higher temperatures for durations equal to the equilibrium annealing times. These results are shown here to be due to the creation of efficient hole traps whose concentration is proportional to the decrease in concentration of Te donors during annealing. The formation kinetics of these traps follows the form Nx(t)=Nx(∞){1−exp[−(t/R)0.44]} where Nx(t) and Nx(∞) are, respectively, the trap densities at annealing time t and at equilibrium, and R is the time constant for the formation process. This process is characterized by an activation energy of about 0.8 eV in the temperature range studied. The above facts when coupled with the observed increase of the 1.22‐eV band emission lead to an identification of the tr...

Dislocations in GaAs17−xPx

Abstract: Dislocations, their origins, and their effects on photoluminescence efficiency have been studied in GaAs1−xPx single crystals grown by vapor phase epitaxy. Dislocations were observed using etch pit, optical‐transmission microscopy, and x‐ray topography techniques. Two types of dislocations are grown into GaAs1−xPx epitaxial crystals. Near the GaAs (substrate)‐GaAs1−xPx interface a high density (>108 cm−2) of pure edge dislocations with axes and Burgers vectors lying in the growth plane was observed. These originate from the lattice parameter mismatch between substrate and epitaxial layer. In the bulk GaAs1−xPx, a high density (∼106 cm−2) of dislocations was observed with 〈211〉 and 〈100〉 directions and Burgers vectors parallel to those of the mismatch dislocations. These dislocations originate from the mismatch dislocations at the substrate‐epitaxial layer interface. The effect of dislocations on photoluminescence efficiency was studied by a novel technique. The photoluminescence was excited by focusing a ...

Electrical and Optical Properties of n‐Type Si‐Compensated GaAs Prepared by Liquid‐Phase Epitaxy

Abstract: The radiative processes in Si‐compensated, n‐type GaAs prepared by liquid‐phase epitaxy have been studied by photoluminescence between 300° and 4.2°K. The data are consistent with the previous hypothesis of the formation under certain growth conditions of two types of acceptor levels by Si in GaAs (in addition to the shallow donor level) with ionization energies of ∼0.03 and ∼0.1 eV. Three basic radiative processes dominate at various temperatures: (a) Band‐to‐band recombination at 300°K, (b) conduction band (or possibly conduction‐band tail states) to shallow acceptor transitions at 4.2°K, and (c) conduction band to the deeper acceptor transitions at 77°K. The half‐width of the third emission band and its peak position depends on the Si and free‐carrier densities. The degree of compensation of these materials is a function of the substrate orientation. Of the three planes investigated, (100), (111)‐Ga, and (111)‐As, growth on the (111)‐As face results in the lowest degree of compensation. The present study shows that n‐type material with mobilities in excess of 1000 cm2/V·sec and electron concentration in the 2–4×1018 cm−3 range can be prepared by growth at 1060°C with the advantage over Te‐ or Se‐doped GaAs that the formation of precipitates of Ga2Se3 or Ga2Te3 is eliminated. Such precipitates were previously shown to seriously degrade the radiative efficiency and hence the performance of injection lasers and spontaneous emitters.

Photoluminescence and Photoconductivity in Undoped Epitaxial GaAs

Abstract: the strength of these forbidden heavy-hole transitions, and we find that the upper bound is at least three orders of magnitude below our noise level for the data in Fig. 1. Ordinary magnetoreflection in InSb measures a maximum AR/R of 10 for allowed transitions. Forbidden transitions therefore produce AR/R of considerably less than 10\". Our laser power (0.3 W/cm) creates a heavy-hole density of ^10 cm for a minority carrier lifetime of 10 sec and a sheath thickness of 10 fi. For kTc^4: meV, 10-cm~ heavy holes produce a fractional population of ~ 10 within about 3kT of the band edge. Hence, the absolute maximum effect of heavy-hole band filling would be 10~, which is three orders of magnitude below our noise level for the data in Fig. 1. The PR structure reported here is most likely due to a periodic modulation of the surface electric field by ree carriers created by the laser beam. We have previously shown that this electric field effect correctly explains the PR effect in GaAs. Another possible mechanism is thermoreflectance due to the periodic heating of the sample by the laser, but from a knowledge of the thermal diffusivity we estimate that the periodic temperature modulation is ~0.013°K—too small to produce significant thermoreflectance. ? We thank K. L. Shaklee for helpful comments on the manuscript. We also thank H. Hodges and R. Epworth for technical assistance.

The Edge Emission and Phonon Effects in the Photoluminescence of CdTe

Abstract: In the photoluminescence spectra of CdTe four series of lines can be resolved in the temperature range 4.2 to 78 °K; each of them is due to the electron transitions involving LO phonons (I. II. III, IV). The relative intensities of these series (the zero-phonon lines at 1.528; 1.539; 1.548; and 1.556 eV at 20°K) depend on the sample temperature and the present impurities. The series I and II are similar in their intensity dependence on temperature to the so-called LT (low temperature, long wavelength) and HT (high temperature, short wavelength) series of the green edge emission of CdS. Series I is dominant in crystals doped with shallow donors; this fact in connection with the temperature dependence and the dependence of the line shape on the excitation intensity leads to the conclusion that it is due to radiative transitions between shallow donors (ED = 0.015eV) and acceptors (EA = 0.0067 eV). The temperature dependence of the intensity of series II and the lines' shape suggest that this series is due to radiative transitions of electrons from the conductivity band to acceptor levels (EA = 0.0067 eV). The variation of the relative intensities of series I and II with the type and content of impurities in the samples correlates with the variation of the relative intensities of the lines in the 1.59 eV region ascribed to the exciton annihilation at donors and acceptors. The distribution of phonon replica intensities in series I and II corresponds to the expression In = I0Nn/n!(n = 0,1,2,…). The changes of the parameter N observed in some cases are due to the overlapping of series I and II with the series III or IV. the nature of which is not quite clear. The variation of the parameter N (which depends on the intensity of the electron-phonon interaction) with the level depth is found to agree qualitatively with the theory of Hopfield. The band at 0.50 eV corresponding to the transitions involving deeper levels shows a structure which may be due to the interaction of electron transitions with local phonons having an energy of 0.045 eV. [Russian Text Ignored].

Effect of Electron-Exciton Collisions on the Free-Exciton Linewidth in Epitaxial GaAs

Abstract: Broadening of the free-exciton emission band with increasing excitation intensity is observed in photoluminescence from GaAs. This effect is quantitatively accounted for by electron-exciton collisions.

PHOTOLUMINESCENCE OF OXYGEN IN ZnTe INTRODUCED BY ION IMPLANTATION.

Abstract: Photoluminescence has been observed from oxygen (O16) ions implanted into ZnTe. Doses of 5 × 1013 oxygen ions/cm2 were implanted at room temperature with energies between 50 and 250 keV. After annealing at 300–400°C in zinc vapor, the characteristic photoluminescence spectrum from the oxygen isoelectronic trap was observed. Care was taken to ensure that the spectrum was a direct result of the implanted oxygen by studying unimplanted and neon‐implanted samples. The anticipated isotope shift was observed in the spectrum for samples implanted with O18.

PHOTOLUMINESCENCE AND STIMULATED EMISSION IN Cd3P2

Abstract: Optically excited recombination radiation is observed in n‐type single crystals of the II–V compound Cd3P2 Line narrowing characteristic of stimulated emission is induced at high excitation intensities

Electroabsorption by Substitutional Copper Impurities in GaAs

Abstract: Previously, Hall effect and other thermal activation measurements have suggested that a copper atom substituted on a gallium site in GaAs is a double acceptor with its first ionization level at 0.145 eV and its second between 0.44 and 0.49 eV above the valence band. Also, previous photoluminescence measurements have revealed broad lines attributable to copper at the Stokes‐shifted positions 0.155 eV and between 0.49 and 0.53 eV. Using an electroabsorption technique, we have studied the spectrum of substitutional copper in GaAs. We find an absorption line associated with a level at 0.463 eV above the valence band for temperatures of 103° and 300°K. We conclude from the selection rules that the wavefunction associated with this level transforms as the Γ6 representation of the double group Td. Except for a weaker additional absorption line (which we do not yet understand) occurring at 0.454 eV in a single p‐type sample, we were able to find no other lines. These results supplement earlier work on the 0.145 e...

Radiative Recombination and Equilibrium between Near‐Band‐Edge Tail States in n‐Type GaAs

Abstract: The detailed balance method of deriving the radiative‐recombination coefficient in semiconductors from the absorption curve is strictly applicable only when thermal quasiequilibrium exists for the carriers within each band It is shown here that in many cases when the bands tail into the gap, the carriers are not in thermal equilibrium within the tail, even quite near the band edge, and that the detailed balance method requires modification A simplified model, that of a regional bandgap variation, is suggested as an approximation to the complex band‐tailing situation It is applied to measurements of photoluminescence and absorption in n‐type GaAs, of varying degrees of degeneracy, and values of the recombination constants at 296° and 77°K are derived They are of the same magnitude as those in ideal material with no tailing An uncertainty arises in degenerate material since it is not clear whether the reduced values of Burstein shift observed are entirely attributable to band shrinkage The contribution of the deeper tail states to the luminescence often appears to be approximately independent of the separation of the state from the band edge

Polishing Damage and Luminescence in p-Type GaAs

Abstract: The photoluminescence of zinc-doped GaAs has been studied for different surface preparations. Mechanically polished specimens fluoresced less than chemically prepared ones. Etch-pit studies using a dislocation etch indicated that mechanical polishing introduced dislocations and samples showing the largest number of etch pits showed the weakest photoluminescence. It was also shown that diffusing a large concentration of zinc into n-type GaAs introduces dislocations, and it is suggested that this is the reason for the low photoluminescence efficiency of zinc-doped GaAs for concentrations in excess of 1019 cm−3. Die Photolumineszenz von mit Zink dotiertem GaAs wurde nach verschiedenen Oberflachenbehandlungen untersucht. Mechanisch polierte Proben lumineszieren weniger als die chemisch praparierten. Atzuntersuchungen unter Benutzung einer Versetzungsatzung zeigen, das beim mechanischen Polieren Versetzungen erzeugt werden und die Proben mit der grosten Versetzungsdichte die schwachste Photolumineszenz zeigen. Es wurde auch gezeigt, das Versetzungen entstehen, wenn Zink mit groser Konzentration in n-leiten-des GaAs diffundiert. Dies ist wahrscheinlich die Ursache fur die geringe Lumineszenz-ausbeute bei mit Zink dotiertem GaAs mit Konzentrationen uber 1019 cm−3.

Photoluminescence (λm = 1.1 μm) in InSe Single Crystals and Its Relation to Photoconductivity

Abstract: An investigation has been made of both the luminescence (λm = 1.1 μm) and photo-conductivity in not intentionally doped photosensitive InSe single crystals. It is shown that the luminescence is due to the emissive capture of free electrons by sensitizing recombination centres. The parameters of the luminescence centres, namely concentration, energetic position, and both electron and hole capture cross-sections have been determined. Es wurden sowohl die Luminesczenz (λm = 1.1 μm) als auch die Photoleitfahigkeit von nicht bewust dotierten. photoempfindlichen InSe-Einkristallen untersucht. Es wird gezeigt, das die Lumineszenz durch strahlenden Einfang freier Elektronen durch sensibilisierende Rekombinationszentren erfolgt. Die Parameter der Lumineszenzzentren, Konzentration. energetische Lage und sowohl Elektronen- als auch Lochereinfangquerschnitte wurden bestimmt.

Luminescence and structure in lead silicate glasses

Abstract: Photoluminescence spectra for a series of glasses of the SiO2K2OPbO system with a constant ratio SiO/K2O and variable quantities from 5 to 60 wt% of PbO were measured. The reduction of the luminescence intensity as function of the emitted energy and the displacement of the maxima towards longer wavelengths with increasing Pb oxide concentrations were noted. Photoluminescence apparently indicates some property which is peculiar to a glass of PbO content of about 20 wt%. The use of the luminescence technique for the study of the structure of glasses in which the photoluminescent element is a macrocomponent is suggested.

Photoluminescence of Aromatic Amino Acids, Synthetic Polypeptides, Proteins, and Cells

Abstract: The photoluminescence of proteins is due to the component amino acids (intrinsic luminescence) or various prosthetic groups if such groups are present in the protein molecule. To investigate structure, one can also examine luminescence protein by means of artificially attached groups (dyes) in which the dye luminesces (secondary luminescence).