Showing papers on "Photoluminescence published in 1974"

Optical absorption and photoluminescence studies of thin GaAs layers in GaAs–AlxGa1−xAs double heterostructures

Abstract: A three‐layered AlxGa1−xAs–GaAs–Alx Ga1−xAs structure has been used to measure the optical absorption and photoluminescence in thin GaAs layers prepared by liquid‐phase epitaxy. The results presented here are for lightly doped n‐type GaAs with free‐carrier concentrations near 1016 cm−3; however, the technique can be used for arbitrarily doped material. The absorption coefficient α was measured between 1.4 and 2.2 eV at 2 and 298 K. The absorption strength at the band gap was found to be (1.15×104)±1000 cm−1 at 2 K and (0.99×104)±1000 cm−1 at 298 K. At 1.96 eV, the energy of the He–Ne laser commonly used for photoexcitation of GaAs, α at 298 K was measured to be 4.4×104 cm−1. A value of 3.8 meV for the room‐temperature exciton binding energy was inferred from the temperature dependence of the interband absorption strength. This value together with previous reflectivity data for high‐purity GaAs gives the energy gap of pure unstrained GaAs at 298 K as 1.424±0.001 eV. The effects of strain due to lattice mis...

Properties of Zn‐doped GaN. I. Photoluminescence

Abstract: Zinc in GaN forms an efficient radiative center emitting blue light at 2.86±0.02 eV and acts as a deep acceptor which can make the crystal insulating. A systematic variation of growth conditions shows that an optimization of the photoluminescence efficiency is possible. Under nonoptimal conditions, lower photon energy emission is obtained. A temperature‐dependent competing nonradiative process has an activation energy of 0.33±0.15 eV. The emission peak exhibits a negligible spectral shift with temperature. The response time of the blue photoluminescence is several orders of magnitude slower than the near‐gap transition. It is suggested that the photoluminescence is due to a radiative transition from the conduction band tail to the Zn acceptor levels.

Photoluminescence at Dislocations in GaAs

Abstract: Photoluminescence measurements with high spatial and spectral resolution on $n$-type GaAs at helium temperatures show the reduction of radiative quantum efficiency immediately at individual deformation-induced dislocations to be orders of magnitude stronger than near grown-in dislocations.

The Synthesis and Photoluminescence of M II M 2 III ( S , Se ) 4

Abstract: The compositions , In were prepared by reaction of the elements in evacuated silica tubes with iodine as a mineralizer. All members except , which is cubic, exhibit the pseudo‐orthorhombic type structure. They are high resistivity p‐type semiconductors; they exhibit Eu+2‐activated fluorescence which varies from red to blue as the electropositive character of the cations increase. Fluorescence activated by Yb+2 is seen at low temperature. Studies were made of the fluorescence decay lifetimes, temperature dependence, excitation spectra, and optical adsorption of : Eu in order to relate the Eu+2‐activated fluorescence to the host bandgap. It is concluded that the most efficient phosphors are those in which the Eu+2 excited states lie farthest from the fundamental edge.

Exciton Interaction in Photoluminescence from ZnO

Abstract: The luminescence spectra of ZnO platelets at 1.9 K have been investigated under 3371 A Insor excitation from 5 to 500 kW/cm2. New details in the P-band luminescence (exciton-exciton scattering) reveal the separation between A and B excitons in ZnO and the stimulated emission in this band is found to be strong for exciton scattering to higher excited states (n > 2). At the highest excitation powers a new emission line is observed which is associated with the decay of excitonic molecules. The molecule binding energy is estimated to be 15 to 20 meV. Es wurdcn die Lumineszenzspektren von ZnO-Plattchenkristallcn bei 1,9 K nntcr Laser-anregung (λ = 3371 A) von 5 bis 500 kW/cm2 untersucht. Ncue Details dcr Lumincszenz der P-Bande (Exziton-Exziton-Streuprozesse) zeigen die Trennung zwischen A- und B-Eszitonen im ZnO, und es wurde beobachtet, dss die stimulierte Emission dieser Bande fur Streuprozesse zu hoheren angeregten Zustanden (n > 2) schr stark ist. Bei den hochsten Anregungen wird eine neue Emissionslinie, die am dem Zerfall der Exzitonenmolekule entsteht, beobachtet. Die Bindungsenergie des Exzitonenmolekuls ist schatzungsweise 15 bis 20 meV.

Liquid Phase Epitaxy of InP

Abstract: Liquid phase epitaxy by conventional tipping technique has been employed for the growth of high purity epitaxial layers. The layers were grown at 720°‐560°C on (100) and (111) oriented InP substrates. Characteristic surface structures for the substrate orientations as a function of the growth temperature were observed. The layers were characterized by Hall data and photoluminescence measurements at low temperatures. The simultaneous observation of the band‐acceptor and donor‐acceptor pair transition due to the main acceptor in our LPE‐layers is reported. The binding energy of this acceptor is determined to .

Si‐defect concentrations in heavily Si‐doped GaAs: Changes induced by annealing

Abstract: Previously reported annealing effects on the carrier density and free‐carrier absorption are correlated with photoluminescence and localized vibrational mode infrared absorption measurements of annealed samples of heavily doped GaAs: Si. Annealing in the range 400≤TA≤750 °C produces the following qualitative changes: (i) a major reduction in the free‐carrier concentration ne, (ii) an increase in the carrier absorption cross section, (iii) a reduction of the SiGa localized mode absorption band, and (iv) the introduction of a new photoluminescence band at 0.98 eV. A defect model is proposed which is consistent with the observed changes. There is a major reduction in [SiGa], the Si donor concentration, which is a function of the anneal temperature between 400 and 750 °C. The reduction is probably through the formation of (SiGa − VGa) pairs. There is little change if any in [SiAs] the Si acceptor concentration. When TA = 400°C the ne = [SiGa] −[SiAs]. When TA = 600 and 750°C, a new acceptor is formed having c...

Optical and channeling studies of ion‐bombarded GaP

Abstract: Below‐gap optical absorption, above‐gap reflectivity, photoluminescence, and He ion channeling backscattering measurements are reported for ion‐bombarded GaP. Each of the four experiments provides a measure of disorder. A one‐to‐one correspondence exists between the absorption, reflectivity, and backscattering measurements, and all three exhibit comparable sensitivity to damage. Photoluminescence is ∼ 100 times more sensitive. The absorption results suggest that every implanted ion species produces amorphous regions associated with each projectile and that these regions have properties very much like those of cold‐deposited amorphous films. The results are interpreted in terms of a model which ascribes these amorphous regions to localized melting followed by rapid quenching to a glassy (amorphous) state in which short‐range tetrahedral order remains intact. The damaged volume per bombarding ion as determined from absorption data is ∼6 times larger than that determined from channeling measurements. Althoug...

Photoluminescence Study of Carbon Doped Gallium Arsenide

Abstract: The photoluminescence studies of the carbon doped epitaxial gallium arsenide revealed that a pair of emission bands at 1.493 eV (B-A) and 1.490 eV (D-A) were attributed to the carbon acceptor on arsenic site. The sharp doublet emission lines at 1.5127 eV and 1.4937 eV were identified with the exciton recombination bound to a neutral carbon acceptor and the two-hole transition in which the neutral carbon acceptor is left in an excited state, respectively. From the observation of these emissions, the 1S3/2 ground and 2S3/2 excited state energies of carbon acceptor were found to be 26.5 meV and 7.5 meV above the valence band edge, respectively. The results were supported by the effective mass arguments and by the dependence of the binding energy on the atomic number of impurities.

Photoluminescence of Zn‐implanted GaN

Abstract: The photoluminescence spectrum of Zn‐implanted GaN peaks at 2.87 eV at room temperature. The emission efficiency decreases linearly with the logarithm of the Zn concentration in the range 1–20×1018 Zn/cm3.

Laser photoluminescence and photopredissociation of Rb2

Abstract: Laser‐photoluminescence studies of Rb2 indicate that the C 1Πu state of the molecule is strongly predissociated. Both fixed frequency ion lasers and a tunable cw dye laser have used been to excite the photoluminescence at pressures from 1 to 100 torr of metal vapor contained in a heat‐pipe oven. The photoluminescence spectra show that the A 1Σu+ and B 1Πu states also are populated following absorption by the C 1Πu state. Recombination collisions between Rb 52P, formed in the predissociation of Rb2, and Rb 52S are proposed to account for the A→X and B→X emission. A strongly pressure dependent quasicontinuum emission is observed in the 540–610 nm region. This emission is attributed to transfer from the C 1Πu state into an unidentified state followed by transitions to high‐lying vibrational and continuum levels of the ground state.

Injection electroluminescence in phosphorous‐ion‐implanted ZnSe p‐n junction diodes

Abstract: Electroluminescence has been obtained from phosphorus‐implanted ZnSe p‐n junction diodes at room temperature. In forward bias, the diodes exhibit an electroluminescence spectrum similar to the red photoluminescence spectrum with a peak at 6300 A giving an external quantum efficiency of 0.01%.

Photoluminescence excitation spectra in amorphous: As2S3, As2Se3 and selenium

Abstract: Photoluminescence excitation spectra in chalcogenide glasses show a rapid fall-off in efficiency at high photon energies, which some authors attribute to surface recombination. This feature is discussed in the light of new experimental data, including luminescence in selenium. It is shown that surface recombination is an unlikely explanation and an excitation-energy dependent quantum efficiency must be assumed. The relationship between photoluminescence and photoconductivity is examined and an earlier model is developed in which the excitation spectrum is explained in terms of enhanced absorption near recombination centres.

Sharp‐line and broad‐band emission in AgGaS2 crystals

Abstract: The low‐temperature photoluminescence spectra of AgGaS2 are investigated in this work. At 4.2°K, the luminescence spectra are dominated by many sharp lines as well as broad emission bands. A series of emission lines was found to be superimposed on the broad band peaking at ∼ 5000 A. The series of emission lines are attributed to phonon‐assisted transitions involving an unidentified impurity or defect. Two basic phonons with energies of 5.4 and 7.2 meV are identified from the phonon structure. The 7.2‐meV mode is also seen in the Raman spectrum. They are tentatively identified as the lattice modes.

Properties of Ge-doped GaAs and Al x Ga 1-x As, Sn-doped Al x Ga 1-x As and Si-Te-doped GaAs

Abstract: In order to better understand the electrical and optical properties of GaAs and AlxGa1-x As used in making double heterojunction lasers, we have studied the Hall coefficient, resistivity and photoluminescence behavior of doped epitaxial samples of these materials. In particular, we report results on Ge-doped GaAs and Alx Ga1-x As, Sn-doped AlxGa1-x As and Si-Te-doped GaAs single crystal layers which were grown on GaAs substrates by the liquid phase epitaxial method. The effects of impurities in the solution on the carrier concentration, mobility, photoluminescence spectra and possible recombination processes in these layers are discussed.

Vapor‐phase epitaxial growth of GaAs in a nitrogen atmosphere

Abstract: GaAs epitaxial growth by the open‐tube AsCl3–Ga–N2 vapor‐transport technique was thoroughly examined as to its growth conditions, with some discussion on an optimum condition supplemented. The results of Hall, impurity profile, and photoluminescence studies for both the epitaxial layers grown in the nitrogen carrier gas and in the hydrogen carrier gas were described for the sake of comparison. A number of experiments successfully revealed a residual impurity in an undoped epitaxial layer. It was found that the present method exceeds the conventional one in many respects when preparing high‐purity uniform epitaxial layers.

Photoluminescence in single-crystal chalcogenides in the system As2Se3-xSx

Abstract: Photoluminescence (PL) and excitation spectra have been measured at temperatures between 5 and 250K single crystals of As2Se3, As2S3 and the mixed system As2Se3-xSx, (0

The photoluminescence properties of glasses in the As-Se system

Abstract: From photoluminescence (PL) studies of the As-Se system it is found that the PL intensity is proportional to As concentration for compositions ranging from 0·3 at% As to As2Se3 Other PL properties are essentially unchanged It is argued that this behaviour provides good evidence that the PL recombination centre is an As broken bond

Excitation Mechanism of Electroluminescent ZnS Thin Films Doped with Rare-Earth Ions

Abstract: Electroluminescence(EL) and photoluminescence(PL) experiments have been carried out on the ZnS: Nd, ZnS: Cu, Cl and ZnS: Cu, Cl, Nd films. The EL emission spectra show two peaks due to Cu-Cl and Nd centers, while the PL emission spectra show only one peak due to Cu-Cl centers. By comparing the efficiencies and the emission spectra of the EL with the PL measurements, it has been clearly shown that the excitation mechanism of the Nd ions in the electroluminescent ZnS: Nd film is via direct impact excitation by hot electrons.

Luminescence, laser, and carrier‐lifetime behavior of constant‐temperature LPE In1−x Gax P (x=0.52) grown on (100) GaAs

Abstract: Photoluminescence and carrier lifetime data are obtained on low‐dislocation‐density (etch pits ≳ 5 × 103/cm2) n‐type In1−x Gax P (x=0.52) epitaxial layers grown on (100) surfaces of GaAs by means of a constant‐temperature liquid‐phase‐epitaxial (CT‐LPE) process. These crystals are of exceptional quality and readily lase from 77 to 300 °K. The index dispersion relation (n‐λ dn/dλ) is determined from the laser mode spacing Δλ in the temperature range 77–300 °K and indicates that at higher thresholds laser operation shifts toward donor tail states. By means of optical phase shift measurements the carrier lifetime (77°K) is examined as a function of wavelength from the spontaneous regime to well above laser threshold. The lifetime data indicate that there is a correlation between a dip in the lifetime due to stimulated emission and the region of the spectrum where the first laser modes appear. These data, and similar data on p‐type crystals, indicate that CT‐LPE In1−x Gax P should be very promising for the de...

Temperature Dependence of Photoluminescence from GaN

Abstract: Photoluminescence intensities, energies, and band shapes of GaN needle crystals are studied as a function of temperature in the range of 4.2–300 K. An emission at 3.472 eV due to a bound exciton localized at a neutral donor site (so-called I2 line) dominates the spectrum at 4.2 K. A donor-acceptor pair recombination band is observed near 3.27 eV. The I2 line quenches with an activation energy of 10±1 meV in the temperature range of 30–80 K, and is not observed at higher temperatures. The activation energy corresponds to the localization energy of the I2-line exciton. The donor-acceptor band quenches at temperatures above 150 K with an activation energy of 160±20 meV, which corresponds to the acceptor binding energy.