Showing papers on "Photoluminescence published in 1972"

Influence of implantation temperature and surface protection on tellurium implantation in GaAs

Abstract: GaAs samples were implanted with tellurium at room temperature or at 150 °C and annealed to 750 °C with an SiO2 or Si3N4 protective layer. The highest electron concentrations and brightest photoluminescence were obtained for the hot implants with a Si3N4 protective layer.

The photoluminescence spectrum of bound excitons in indium phosphide and gallium arsenide

Abstract: Photoluminescence spectra of refined epitaxial indium phosphide and gallium arsenide show clearly a close correspondence of bound exciton transitions. Classified in both materials are emissions due to excitons bound to neutral acceptors and donors, free exciton peaks and various types of phonon coupling. Excitons bound to neutral acceptors in both materials give rise to a sharp doublet emission which readily reveals the presence of strain in the sample. The magnitude of the strain is estimated to be approximately 10-3 in certain regions of typical epitaxial layers. Reflectivity experiments provide new estimates of the exciton gaps-1.4182 eV in indium phosphide and 1.5150 eV in gallium arsenide.

Liquid phase epitaxial growth of Ga x In 1-x P

Abstract: Single crystal epitaxial layers of Gaxln1−xP alloys have been grown by the steady-state liquid phase epitaxial growth technique on (111)B GaAs substrates. The crystal growth process has been studied in detail and the resultant epitaxial layers have been characterized with respect to their structural, electrical and optical properties. Epitaxial layers of good structural quality could be grown only in the composition range x = 0.48 to 0.53, where the lattice parameter is close to that of the GaAs substrate. The band gap of these crystals was in the range 1.86 – 1.92 eV as determined by optical absorption and photoluminescence measurements.

Spontaneous‐ and Stimulated‐Emission Spectra of CdSnP2

Abstract: We report the band‐edge photoluminescence spectra of CdSnP2 crystals lightly doped with Cu or Ag. The emission from CdSnP2:Cu is dominated by a broad band 0.13 eV below the band gap at 1.240 eV (2°K). The emission from CdSnP2:Ag is much stronger and is dominated by a narrow band‐to‐band emission with three impurity peaks at slightly longer wavelengths. At the very high excitation levels, possible with a pulsed N2 laser, a new band appears ∼ 15 meV below the band gap in CdSnP2:Ag, grows superlinearly in the excitation level, and has other features indicating stimulated emission. Indeed, in crystals suitably prepared to form Fabry‐Perot cavities, narrow‐line laser emission is observed. Studies in a magnetic field reveal that the spontaneous band‐to‐band transition and the new stimulated line shift to higher energies at precisely the same rate indicating that they result from the same recombination mechanism. From the observed shift to higher energies, it is argued that exciton‐exciton scattering can be unambiguously eliminated as the laser mechanism. As briefly reported previously, it is shown that the magnitude and field dependence of the shift requires proper account of electron‐plasmon (plasmaron) coupling.

Electrical Transport and Photoelectronic Properties of ZnTe:Al Crystals

Abstract: A study of native and impurity defect levels in Al‐doped high‐resistivity ZnTe is described. Experimental information includes electrical transport, photoluminescence, and photoconductivity measurements. Analysis of this information led to the following defect‐level assignments: an acceptor level 0.25 eV from the valence band, attributed to a Zn‐vacancy‐Al‐donor complex; an acceptor level 0.60–0.65 eV from the valence band, assigned to a native defect, possibly the second level of a zinc vacancy; and a donor level 0.1 eV from the conduction band, assigned to the dopant aluminum. These levels are involved in radiative recombination which gives rise to three photoluminescence bands with peaks near 2.11, 2.04, and 1.63 eV at 77 °K, observed in Zn‐vapor‐annealed ZnTe : Al single crystals.

Deep hole traps in n‐type liquid encapsulated Czochralski GaP

Abstract: Cathodoluminescence and photoluminescence time‐response measurements have been used to study the prominent luminescence bands in n‐type GaP grown by the liquid‐encapsulated Czochralski (LEC) method. In as‐grown crystals, two deep hole traps are identified. An isoelectronic hole trap, ≃0.4 eV above the valence band edge, produces red emission (1.72 eV) due to bound‐exciton and pair recombination, while infrared luminescence (1.51 eV) is produced by pair recombination between a deep (≃0.7 eV) acceptorlike center and the donor dopant. In certain heat‐treated samples, an additional structured luminescence band is produced at 2.07 eV, which also apparently results from recombination at an isoelectronic center. Resolution of the no‐phonon lines of this emission suggests that an exciton is bound by 186 meV to the impurity center created by annealing. Although no positive identification of the chemical nature of these defects has been possible, we find that our results are not inconsistent with previously suggest...

Photoluminescence of AlxGa1−xAs

Abstract: We present the results of a detailed study of the photoluminescence spectra of epitaxially grown AlxGa1−xAs for 0.16≤x≤0.58 and for temperatures between 1.6 and 300°K. At helium temperatures, the emission spectrum consists of a narrow band (half‐width ∼ 10 meV) and a broad band (half‐width ∼ 30 meV) for direct‐ as well as indirect‐gap alloys. From temperature and excitation intensity dependence and from time‐resolved spectra, we we have identified the broad band as due to distant donor‐acceptor pair recombination. The narrow band is very likely due to free‐ and bound‐exciton recombination. These identifications differ from those suggested by others. At room temperature, the emission spectrum consists of a single peak with a long high‐energy tail. This emission is due to the direct band‐to‐band transition even in the case of indirect band‐gap materials with x<0.5. Temperature‐dependence data suggest that the temperature coefficient of the direct band gap is a function of x.

Chapter 5 Photoluminescence II: Gallium Arsenide

Abstract: Publisher Summary This chapter reviews the photoluminiscence properties of GaAs. Helium–neon laser is used for photoluminescence measurements on GaAs. In addition, microphotoluminescence using a laser has proved to be an invaluable tool for the study of compositional inhomogeneities in thin epitaxial layers of mixed crystals such as Ga(As, P). Photoluminescence has proved itself to be very useful for the assessment of semiconductor materials. One can calculate carrier concentrations at a fixed temperature or the concentration change as a function of temperature, it is also possible on combining absorption and luminescence measurements to work out the lifetime and the diffusion length of minority carriers. In addition, threshold currents of diffused GaAs lasers have been related to the near-band-edge photoluminescence intensity of the n-type substrate which has been diffused with p-type impurities. The largest unsolved problem is the role of nonradiative recombination. There is no doubt that it is extremely important because all III-V compounds show a considerable enhancement of luminescence intensity on being cooled to low temperatures. This increase in intensity can only partially be related to the change in the position of the Fermi level and the consequent emptying of traps. Auger transitions involving free carriers alone and free carriers and impurities must be taken into account as well as additional nonradiative recombination at localized centers and at dislocations and radiative recombination via deep impurities.

Indirect, Γ8v‐X1c, band gap in GaAs1−xPx

Abstract: The indirect band gap of GaAs1−x P x has been determined accurately over a large alloy composition range. The results were obtained with a wavelength derivative technique in optical absorption on material grown under complete equilibrium conditions. Zero‐phonon as well as momentum‐conserving phonon‐assisted free‐exciton transitions were observed. A distinct curvature in the direct band gap‐vs‐alloy composition curve is determined. Photoluminescence measurements of the same samples, together with the absorption edge data, give the alloy composition dependences of the energies of donor‐acceptor pairs and bound excitons; thus the intrinsic nature of the transitions observed in absorption is established.

Electric field quenching of photoluminescence in poly‐n‐vinylcarbazole

Abstract: THERE has been considerable work done on the effect of an applied elect& field on luminescence, particularly with inorganic phosphors [ 11. Bernanose [2] has studied the enhancement effect of previous exposure to light on the electroluminescence in vinylcarbazole, and the dependence on electric field of the optical generation of free carriers in poly-N-vinylcarbazole (PVK) has been demonstrated [3]. In this note the effect of an applied electric field in partially quenching the photoluminescence of PVK is reported. To the author's knowledge, this is the first reporting of an electric field effect on photoluminescence in an organic material. PVK pellets were obtained from two commercial sources. As determined by atomic emission spectroscopy, PVK from one source contained metallic impurities in the several hundred ppm range, while the other source had less than 10 ppm metallic impurity. The effect was observed in both samples but only data from the low metal samples will be presented. Polymer samples were prepared by dissolving the PVK in a 4 : 1 by weight solution of toluene : cyclohexanone. The polymer solution was flow coated onto 1 cm square conducting, transparent tin oxide coated glass substrates, air dried, and baked in air at 70°C for 30 min. Thicknesses were in the 5 to lox cm range, as measured by a micrometer accurate to 1 X cm. The micrometer thickness measurements agreed well with two other estimates of the thickness. If the maximum field to which the samples could be charged is computed from the maximum voltage and measured thickness the result of 1.5 X 106 V/cm agrees well with previous measurements of 1.4 X 106 V/cm[3]. In addition, the surface charge was measured independently of the surface voltage in separate measurements by a technique described elsewhere [4,51. In this way the sample capacitances were measured. Using a dielectric constant of 3.75 [3], the thickness determined by the capacitance measurement was within 15 per cent of that measured with the micrometer. Thus, the micrometer was considered sufficiently accurate and it was used to measure sample thicknesses. The apparatus is shown schematically in Fig. 1. Electric fields of up to 1.5 X 106 V/cm were applied by depositing in the dark on the free PVK surface a positive charge from a high voltage corona discharge in air. Since these techniques for obtaining high electric fields are not well-known outside of electrophotographic research [6, 71, a detailed description of the apparatus for sample charging and voltage measurement

Impact Ionization of Donors in Semiconductors as a Tool for Photoluminescence Investigations

Abstract: Impact ionization of impurities can serve as a tool for investigations of radiative recombination mechanisms in semiconductors. Additional information can be obtained on the degree of compensation. The effectiveness of the method is demonstrated for n‐type GaAs. Four different bands are proved to be caused by donor‐acceptor transitions. The degree of compensation is found to be high in our samples.

Defect Studies of GaP Crystals Pulled from Nonstoichiometric Melts: Dislocation and ``Saucer'' Etch Pits

Abstract: It has recently been shown that the occurrence of flat‐bottomed saucer‐shaped etch pits (S‐pits) in GaP grown by the liquid‐encapsulated‐Czochralski (LEC) technique can be correlated with reduced photoluminescence (PL) and electroluminescence (EL) efficiencies. At the same time a new class of LEC crystals pulled from nonstoichiometric melts (LEC/NSM) have become available which show much improved PL efficiencies (η). A study of the etchpit densities in LEC/NSM crystals was therefore carried out. Both p‐ and n‐type material were examined. In n‐type material the S‐pit density is reduced by at least 4 orders of magnitude for all LEC/NSM crystals compared with LEC material. Similar reductions in S‐pit density are observed in p‐type material, but only for crystals pulled from melts containing less than 30 at. % phosphorus. This correlates well with those p‐type crystals showing major improvements in PL η. However, crystals pulled from 20 and 10 a/o P melts are small in size and have a strong tendency to entrai...

Scanned-laser microscope for photoluminescence studies

Abstract: A scanned-laser microscope has been developed to generate photoluminescence maps, or images, of semiconductor samples. This instrument is shown to be extremely useful for evaluating semiconductor wafers, especially those intended for light-emitting diodes. The design and construction of this new microscope are discussed, and performance tests of a prototype are presented. The photoluminescence microscope achieves a spatial resolution near 10−3 cm with a spectral definition of 100 A and examines an area 0.6 cm on a side in a few seconds. Examples of the application of the photoluminescence microscope to testing of GaAsP wafers are presented and compared with the results of other kinds of tests to determine the suitability of these wafers for light-emitting diodes.

Radiative Recombination in Cadmium Sulfide

Abstract: Luminescent centers involving Ag impurities were introduced into CdS single crystals through doping with 109Cd radioisotopes. Thus, the Ag concentration increases with time as more 109Cd decays. This enables a study of photoluminescence versus Ag concentration in a given crystal without changing the concentrations of other impurities.A new emission band at 5600 A results in addition to the 6100 A band present in Ag-doped crystals using conventional techniques. This new emission is quenched with increasing Ag concentration at high concentrations. Also concentration quenching by the Ag impurities occurs for the green edge, and the bound-exciton emissions I1, and I2. The quenching is explained by assuming a donor–acceptor recombination process.The new emission probably arises from the recombination of a bound electron with a bound hole at a distant donor–acceptor pair, with Ag as the acceptor. The acceptor role of Ag is supported by electrical conductivity measurements on 109Cd-doped crystals. Estimates are ...

Mg–O Complexes in GaP—A Yellow Diode

Abstract: A yellow‐orange luminescence which peaks at 6030 A at 300 °K has been observed in (Mg, O)‐doped GaP and is attributed to a bound excitonic transition at a nearest‐neighbor Mg–O complex. A photoluminescent efficiency at low temperatures of ∼20% has been measured and yellow diodes of external quantum efficiency ≃0.1% at 77 °K have been fabricated.

Photoconductivity and photoluminescence of amorphous chalcogenides

Abstract: Experimental data on photoconductivity and photoluminescence of amorphous chalcogenides are reviewed and are examined by means of a simple model in which most of the carriers created by the light drop into localized states before recombining bimolecularly.

Evidence for a primarily nonradiative Si,O defect in GaP

Abstract: Experimental evidence is presented to establish the existence of a Si,O defect impurity system in GaP. This defect is shown to be a strong nonradiative recombination center in n‐type material. A photoluminescence band near 1.55 eV at room temperature has been associated with the Si,O defect.

Concentration Quenching and Depolarisation of Photoluminescence in Solutions

Abstract: Abstract The emission anisotropy r/r0 and quantum yield η/η0 of the photoluminescence of glycerin-water solutions of Na-fluorescein has been measured at concentrations 10-6 - 3·10-1 M. The drop of η/η0 is connected with a repolarisation effect, which is interpreted by a completed theory of con-centrational depolarisation of photoluminescence (CDPL), accounting the self-quenching by non-luminescent dimers and the remigration of excitation energy. The dimerisation constant and the critical concentrations have been determined.

Green Electroluminescence in ZnSe–ZnTe Heterojunctions by Liquid‐Phase Epitaxial Growth

Abstract: ZnSe–ZnTe heterojunctions prepared by liquid‐phase epitaxial growth method exhibited green electroluminescence with the peak of about 5350 A at 77°K. The photoluminescence at 77°K from uv excitation was also measured and it was found that the green emission seems to result from hole rather than electron injection.

Sensitization of rare earth photoluminescence in II-VI compounds. II. Site sensitive excitation mechanisms in zinc selenide

Abstract: For Pt. I see ibid., Vol. 4, 2962 (1971). The authors report on an experimental study of the excitation of Er3+ emission in ZnSe. It is shown that two rare earth luminescent centres both emitting from the 4S3/2 level are excited by the resonant transfer of energy from two different broad bands. It is thus concluded that the transfer of energy from a broad band emission to any rare earth ion in the II-VI lattice, simply because of an energy overlap, does not take place as the local environment of the rare earth ion plays a significant part in the transfer process.

The role of Ga2O3 in the preparation of Y2O3:Eu3+ phosphor from the oxides

Abstract: It has been observed that Ga2O3 enhances the cathodeluminescence and the 2537 A-excited photoluminescence, and also causes whitening of the body colour of Y2O3:Eu2+ prepared from the oxides. In both types of luminescence, these effects are apparently due to the Ga2O3 behaving as a mineraliser, i.e. a diffusion enhancer. In the case of photoluminescence, additional brightness enhancement resulting from incorporation of Ga2O3 is due to a type of sensitisation to the exciting wavelength.