Showing papers on "Photoluminescence published in 1980"

The effect of As2 and As4 molecular beam species on photoluminescence of molecular beam epitaxially grown GaAs

Abstract: The first observation of several sharp photoluminescence lines with energies less than the energy of the recombination peak associated with the exciton bound to the neutral carbon acceptor in nominally undoped p‐type GaAs grown by molecular beam epitaxy (MBE) is reported. The lines ranging from 1.5110 to 1.5040 eV are interpreted as radiative recombination of defect‐induced bound excitons directly correlated with the interaction of As4 molecular beam species during MBE growth. These lines disappear totally when As2 instead of As4 beams are used. We then demonstrate that all sharp photoluminescence features, previously only detected in the best LPE samples, are now also observed in thin MBE GaAs layers when grown from As2 beam species.

Physics of nonlinear transport in semiconductors

Abstract: The Lectures.- 1. Phenomenological Physics of Hot Carriers in Semiconductors.- The Carrier Temperature Model.- Drift, Diffusion, and Generation-Recombination of Hot Electrons.- The Influence of Classical Magnetic Fields on Hot Electrons.- Hot Electrons in Semiconductor Devices and Layered Structures.- Appendices,.- 2. Electronic Structure of Semiconductors.- The Single Particle Description: Bonds and Bands.- Many-Body Effects on the Electronic Structure of Semiconductors.- 3 The Electron-Phonon Interaction in Semiconductors.- The Adiabatic Approximation.- The Deformation Potential Interaction.- Non-polar Optical Phonon Scattering.- Polar-Optical Interaction.- Piezoelectric Interaction.- A Microscopic Approach.- Applications.- The Electron-Phonon Interaction in Nonperfect Semiconductors.- 4. Semi-Classical Boltzmann Transport Theory in Semiconductors.- Displaced Maxwellian.- Numerical Techniques.- 5. Quantum Transport Theory.- Concepts.- Structure of High Field Quantum Kinetic Theory.- Many-Body Formulation and the Screening Problem.- 6. Carrier-Carrier Interactions and Screening.- The Intercarrier Interaction.- The Critical Concentrations.- Distribution Functions.- 7. Multiphonon Scattering.- Electron-multiphonon Processes.- Electron-Two phonon Processes.- Results.- Summary.- 8. Experimental Studies of Nonlinear Transport in Semiconductors.- Transport Parameters.- Electron Temperature.- Hot Electron Distribution Functions.- Conclusions.- 8a. Time-of-Flight Techniques..- Description of ToF Techniques.- Types of Information Available from ToF Techniques.- Alternative Techniques.- Summary of ToF Most Significant Applications.- 9. Hot-Electron Transport in Quantizing Magnetic Fields.- The Shubnikov-de Haas Effect.- The Magnetophonon Effect.- Magneto-Impurity Resonance.- 10. Hot Electron Distribution Function in Quantizing Magnetic Fields.- Quantitative Estimates of Electron Temperature.- Study of the Electron Distribution Function in Crossed Fields.- Conclusions.- 11. Hot Electron Effects in Semiconductor Devices.- Transient Hot Electron Effects in Semiconductor Devices.- Conclusions.- 12. Optical Excitation of Hot Carriers.- Optical Excitation of Electron-Hole Pairs.- Carrier Heating by Optical Injection.- Band Filling by Optical Excitation.- Oscillatory Photoconductivity and Photoluminescence.- Conclusions.- 13. Theoretical Concepts of Photoexcited Hot Carriers.- The Barker-Hearn Model.- Solution of the Integral Equation.- Photoexcited Holes in Cu-Doped Germanium.- Effects of Optical Phonons, 360 Further Physical Effects.- 14. The Physics of Nonlinear Absorption and Ultrafast Carrier Relaxation in Semiconductors.- Review of the Germanium Band Structure.- Physical Processes.- Initial Models.- Conclusion.- 15. Nonequilibrium Phonon Processes.- Phonon Instabilities.- Phonon Lifetimes.- Steady-State Effects of Nonthermal Phonons.- Some Further Aspects of PH-Disturbances in Solids.- 16. Noise and Diffusion of Hot Carriers.- Fluctuations and Noise: General Considerations.- Noise Temperatures of Hot Carriers.- Diffusion of Hot Carriers.- Experimental Techniques.- Theoretical Determinations.- Noise Sources.- Noise of Hot Carriers in Devices.- Some Quantum Effects.- Conclusion.- The Seminars.- 1. High-Field Transport of Holes in Elemental Semiconductors.- Theoretical Model.- Results and Discussion.- Conclusions.- 2. Nonlinear Transport in Quasi-One-Dimensional Conductors.- Nonlinear Transport in Organic Charge Transfer Salts: TTF-TCNQ and Related Compounds.- Non-Ohmic Effects in KCP.- Non-Ohmic Conductivity of Quasi-ID Trichalcogenides: NbSe3.- Nonlinear Transport in Highly Conducting Polymers.- Summary.- 3. Optical Absorption of Solids Under Laser Irradiation.- Band Structure Effects.- Optical Properties.- Conclusions.- 4. High Intensity Picosecond Photoexcitation of Semiconductors.- Dynamic Saturation of the Optical Absorption.- High Photogenerated-Carrier Densities.- Hot Phonons,.- The Relaxation-Diffusion-Recombination Model.- Summary.- 5. Hot Electron Contributions in Two and Three Terminal Semiconductor Devices.- Two-Terminal Devices.- Three-Terminal Devices.- 6. Modeling of Carrier Transport in the Finite Collision Duration Regime: Effects in Submicron Semiconductor Devices.- The Intracollisional Field Effect.- The Retarded Equations.- Discussion.- 7. On the Physics of Sub-Micron Semiconductor Devices..- Physical Scales and Phenomena.- On Medium Small Devices.- Very Small Scale Devices.- Synergetic Effects and New Device Concepts.- Formal Theory of Coupled Device Arrays.- List of Participants.

Shallow-acceptor, donor, free-exciton, and bound-exciton states in high-purity zinc telluride

Abstract: Photoluminescence was measured at 1.6 K on ZnTe crystals, both nonintentionally doped high-purity and lightly P- or As-doped samples. Luminescence was excited mostly with a tunable dye laser close to the band gap. Ground states of the shallow-acceptor bound excitons are identified and attributed to the various acceptors by means of excitation spectra taken on two-hole satellites of these bound-exciton lines. Excited bound-exciton states are also obtained from the excitation spectra. The coupling of the electron and holes in the bound-exciton states appears to be very different for the various acceptors even for almost identical exciton localization energy. The excitation spectra of these two-hole luminescence satellites also exhibit negative spectral features attributed to the free-exciton $1S$, $2S$, and $3S$ levels. We derive the free-exciton binding energy ${E}_{\mathrm{FE}}(1S)=13.2\ifmmode\pm\else\textpm\fi{}0.3$ meV and the band-gap energy ${E}_{g}=2.3941\ifmmode\pm\else\textpm\fi{}0.0004$ eV. Excitation spectra were also taken on the donor-acceptor pair bands involving the Li, P, As, and the Cu acceptor. These excitation spectra yield $s$ and $p$ symmetric excited acceptor states and also excited donor levels. The latter yield 18.3 \ifmmode\pm\else\textpm\fi{} 0.3 meV binding energy of the predominant shallow donor. Higher excited $\mathrm{nS}$ states ($n\ensuremath{\ge}4$) for the Cu, Li, Ag, and the still unidentified $k$ acceptor are derived from two-hole series measured on unintentionally doped samples. Our results thus represent the most complete information available to date on excited shallow-acceptor states in ZnTe. The donor-acceptor pair excitation spectra contain features due to the creation of $\mathrm{TO}(\ensuremath{\Gamma})$ and $\mathrm{LO}(\ensuremath{\Gamma})$ phonons and also impurity-dependent lattice vibrations. Two-electron satellite lines are observed for resonant excitation at the shallow-donor bound exciton. The results agree with those from the excitation spectra taken on the various donor-acceptor pair bands.

Photoluminescence of shallow acceptors in epitaxial AlxGa1−xAs

Abstract: The low‐temperature (2 K) photoluminescence (PL) of AlxGa1−xAs (0

Near‐band‐edge photoluminescence in ZnSe grown from indium solution

Abstract: The near‐band‐edge photoluminescence of ZnSe crystals grown from an In solution has been studied in order to elucidate a transition mechanism of the room‐temperature blue emission band which is typically observed in the photoluminescence of the low‐resistivity ZnSe crystals and the electroluminescence of the ZnSe diodes of metal‐insulator‐semiconductor (MIS) structure. On the basis of the temperature‐dependent behavior of the various near‐band‐edge emission bands, i.e., changes in the peak energies and the intensities over the wide temperature range, the room‐temperature blue emission is attributed to the recombination between free holes and donor electrons. Special attention is paid to a relation between this emission and the low‐temperature exciton emission due to the recombination of excitons bound to the ionized donor.

The influence of spin defects on recombination and electronic transport in amorphous silicon

Abstract: Photoluminescence, photoconductivity, and dark hopping conductivity of a-Si : H have been measured as a function of defect concentration. The network defects were created by electron bombardment and by hydrogen effusion. Both methods were successively applied to samples prepared in the same run. The defect concentration was monitored by spin resonance measurements. Our results can be explained with the assumption of essentially two kinds of defect : dangling-bond and vacancy-type defects. It is necessary to assume a positive effective correlation energy for both kinds of defect.

Evidence for Exciton Localization by Alloy Fluctuations in Indirect-Gap Ga As 1 − x P x

Abstract: This paper reports a new photoluminescence (PL) band in indirect $\mathrm{Ga}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ that lies between donor-bound and free exciton PL peaks. It has relatively strong $X$-point phonon sidebands and an asymmetric shape with an abrupt high-energy cutoff. The lifetime varies rapidly over the PL linewidth. Properties of excitons in fluctuating random-alloy potentials are discussed. It is suggested that this line is due to excitons trapped by such potentials.

White photoluminescence of amorphous silicon‐carbon alloy prepared by glow‐discharge decomposition of tetramethylsilane

Abstract: An amorphous film of silicon‐carbon alloy with approximate composition Si0.1C0.9 was prepared on a fused‐quartz, a glass, or a silicon wafer by the glow‐discharge decomposition of tetramethylsilane. The film has an optical gap energy as large as 2.8 eV and shows white photoluminescence even at room temperature due to its broad emission band over the whole range of the visible spectrum. The photoluminescence is observable for the films deposited at substrate temperatures below 300 °C.

Radiative transitions induced in gallium arsenide by modest heat treatment

Abstract: Photoluminescence spectra from three species of n‐GaAs, lightly Si doped, heavily Si doped, and lightly Te doped, show the onset of additional radiative transitions upon modest annealing in the 550–700 °C range. Etch‐back procedures reveal that the new structure is all surface related. It is attributed to the creation of arsenic vacancies at the surface which allow electrical activation of silicon donors, enhance the probability of silicon site exchange, and lead to complex formation involving both donor and acceptor levels.

Modifications in Optoelectronic Behavior of Plasma-Deposited Amorphous Semiconductor Alloys Via Impurity Incorporation

Abstract: We discuss electronic properties of plasma-deposited a-Si:H alloys as functions of oxygen and nitrogen impurities. Over a wide range of processing conditions, features displayed by the data include: i) “anomalous” behavior in photoconductivity versus temperature for films deficient in either, or both, impurities (peaks appear that are associated with thermal-quenching processes and supralinearity); and ii) modification to “classic” behavior in photoconductivity owing to synergistic effects of oxygen and nitrogen . Correlations with photoluminescence are presented. Optical emission spectroscopy is discussed within the context of an emerging spectroscopy for the detection of emitting reactive species in the plasma. The presence of impurities, particularly N 2 , can be diagnosed.

Room‐temperature photoluminescence in spray‐pyrolyzed CdS

Abstract: Very intense room‐temperature photoluminescence has been observed near 1000 nm in CdS films prepared by spray pyrolysis. Since this material can be easily fabricated into p‐n devices, this suggests the possibility of inexpensive electro‐optical devices. Also, the photoluminescence spectra of CdS and amorphous Si:H are very similar.

Deep electron traps in organometallic vapor phase grown AlxGa1−xAs

Abstract: Deep electron traps have been studied by means of deep level transient spectroscopy in n‐type nominally undoped and intentionally Te‐doped AlxGa1−xAs epitaxial layers which were grown by vapor phase epitaxy from organometallic compounds (OMVPE). Three main deep electron levels are present in undoped material: a trap with an activation energy of 0.8 eV, which is also found in GaAs grown by conventional VPE, and two levels specific to OMVPE with activation energies of 0.32 and 0.38 eV, respectively. The concentration of the 0.8 eV level is found to be independent of the aluminum content x, supporting the assumption that it is not related to substitutional oxygen. The other levels, however, exhibit a very strong dependence of concentration on the composition, varying by four orders of magnitude in the range of 0⩽x⩽0.35. In Te‐doped samples, a level with an activation energy of 0.23 eV has been identified, which is thought to be related to an IR emission found in photoluminescence in OMVPE as well as in liqui...

Bandgap Energy of InGaAsP Quaternary Alloy

Abstract: The bandgap energy of InGaAsP quaternary alloy lattice-matched to InP has been precisely determined by electroreflectance (ER) measurements. The ER spectra show the typical low-field ER lineshape over the whole alloy composition range, and this has enabled us to determine the precise bandgap energy of the InGaAsP alloy easily. It was found that the bandgap energy Eg of the In1-xGaxAsyP1-y alloy lattice-matched to InP is written as Eg=1.35-0.738y+0.138y2 at room temperature as a function of the As composition y. We have also measured the photoluminescence spectra of the InGaAsP samples, and found that the peak energy of the photoluminescence spectrum, which is frequently used as a measure of the bandgap energy, is slightly different from the precise bandgap energy determined by ER measurements.

Properties of Zn‐doped VPE‐grown GaN. II. Optical cross sections

Abstract: Experimental data are presented for optical cross sections σ0n(hν) related to the four deep acceptorlike Zn‐related radiative levels A–D in GaN. Very accurate spectral data were obtained by the photoluminescence excitation (PLE) technique, at temperatures varying from 4.2 up to 293 K. From a detailed comparison of the spectral behavior of the emission and absorption spectra, the size of electronic broadening effects could be determined in the overlap region. The binding energies for Zn‐related acceptor levels were obtained as EA=0.34±0.04, EB=0.65±0.08, EC=1.02±0.05, and ED=1.42±0.08 eV at low temperature. Optical transmission data give estimates of absolute values for optical cross sections at saturation, varying from σ0nA(sat) ?1×10−16 to σnD(sat) ?5×10−18 cm2. Temperature broadening effects in optical cross sections are well explained by a linear model for phonon coupling in the optical transitions, employing the same phonon energies and coupling strengths as were evaluated from emission spectra.

Photoassociation, photoluminescence, and collisional dissociation of the Sr2 dimer

Abstract: We report observations and analysis of the laser‐excited photoluminescence of Sr2. The spectra contains some discrete molecular line spectra, but is dominated by extensive, deeply modulated continua characteristic of bound–free transitions of excimer systems. Dye laser and argon laser excitation of the Sr2 dimer is used. Some of the spectra is attributed to fluorescence from dimers created by laser induced photoassociation of free Sr atoms. Techniques are developed to obtain Morse potential parameters by computer modeling of the observed spectra. We find for the X 1Σ+g state, De=1100±100 cm−1, ωe=39.6±1 cm−1; for the A 1Σ+u state, De=5460±100 cm−1, ωe=83±3 cm−1; and Re″−Re′=0.49±0.02 A. Strong collision‐induced predissociation is observed and attributed to a potential curve crossing. Cross sections for dissociation by argon are reported as a function of laser excitation wavelength.

Hot‐carrier relaxation in photoexcited In0.53Ga0.47As

Abstract: Photoluminescence spectra of In0.53Ga0.47As reveal the presence of hot carriers with effective temperatures as high as Tc ∼600 K. Variation of carrier temperature with excitation intensity identifies the LO phonon emission process as the dominant carrier cooling mechanism with h/ωLO=34 meV. Comparison with GaAs yields a hot‐carrier energy loss rate a factor of 3 smaller for the less polar In0.53Ga0.47As.

Luminescence in slipped and dislocation‐free laser‐annealed silicon

Abstract: Photoluminescence of cw laser‐annealed silicon shows a dramatic difference in electronic behavior of the reconstructed material depending upon either creation or suppression of dislocations. Beyond a critical exposure time slip appears, and the luminescence of these samples is dominated by dislocation‐related defect levels.

New Complex Fluorides EuMgF4, SmMgF4, SrMgF4, and Their Solid Solutions: Photoluminescence and Energy Transfer

Abstract: Three previously unknown compounds, , , and , and solid solutions, have been prepared by a method involving the use of Mg metal as a reducing agent for the Eu and Sm. Both and appear to be excited via a 4f → 5d transition (broad band). emits a bright blue under 356 nm peak excitation, the emission peak being at 437 nm. has sharp line emission assigned to transitions. In solid solutions , maximum efficiency is found at and the efficiency of is only about 5% less, adding to the small group of known "stoichiometric phosphors." This is correlated with magnetic measurements which show little or no exchange interaction between neighboring rare earth ions. The magnetic behavior of the Sm2+ ion in suggests the possibility of mixing of the and states of the ground state manifold, owing to strong acentric crystal fields. In solid solutions, there is remarkable energy transfer from Eu2+ to Sm2+, the Eu2+ emission being barely detected at and completely absent at higher Sm concentrations. Evidence for both radiative and nonradiative transfer was found, but the nonradiative mechanism appears to predominate.

Photoluminescence in sputtered amorphous silicon-hydrogen alloys

Abstract: Results of photoluminescence (PL) experiments performed on amorphous silicon-hydrogen alloys prepared by sputtering in a plasma containing hydrogen are presented. A single, featureless peak centred near 1.3 eV and of 0.3 eV f.w.h.m. is observed upon excitation with 2.4 eV light in alloys of hydrogen concentration cH≥5 at.% held at temperatures below 200 K. The PL quantum efficiency and peak energy are increasing functions of ch. A high-temperature decrease in PL is observed, and electric fields of 105 V/cm are found to be sufficient to quench the PL. It is contended that the original argument in the literature concerning the necessity for Stokes shifts of the order of 0.5 eV is wrongly based. From the present data we conclude that radiative recombination in our films may best be viewed in the framework of a rigid-band model with only small perturbations caused by distortional effects of the host matrix. The high-temperature thermal quenching of the PL is analysed in terms of two quenching mechani...

Photoluminescent thermometer probes: temperature measurements in microwave fields

Abstract: Based on luminescence, the photoluminescent thermometer can in principle function in electromagnetic field coupling and perturbation. Several prototypal probes that have been constructed and tested demonstrate the feasibility of the concept. Temperature resolution of approximately 0.3 degrees C has thus far been achieved. The probes are needle-shaped, sturdy and less than 1 millimeter in size. This thermometer system has excellent potential application in monitoring and controlling tissue temperatures when microwaves are used to induce hyperthermia for cancer treatment.

Photoluminescence from E band centers in amorphous and crystalline SiO2

Abstract: Photoluminescence (PL) originating from intrinsic defects in neutron-irradiated crystalline (x-) SiO 2 is observed and compared with that from amorphous (a-) SiO 2 . The PL and photoluminescence excitation (PLE) spectra of x-SiO 2 are qualitatively similar to those of a-SiO 2 . This suggests that PL centers, similar to those found in amorphous systems, are present in ordered systems. In addition, the PL and PLE spectra a-SiO 2 and a-As 2 S 3 scale with energy band gap, suggesting that the radiative processes in a-SiO 2 and semiconducting chalcogenide glasses are alike. The similarity of the PL from x-SiO 2 to that from a-SiO 2 and the scaling of the PL from a-SiO 2 and a-As 2 S 3 with energy band gap strongly suggest that PL centers are unique bonding configurations which primarily depend on the chemistry of the system rather than on the degree of long range order.

Photoluminescence excitation spectroscopy of 3d transition-metal ions in GaP and ZnSe

Abstract: Photoluminescence and photoluminescence excitation spectra are presented for ZnSe:Ni, GaP:Co and GaP:Ni. Comparison of the excitation spectra with published absorption spectra leads to the identification of Ni2+(d8) as the luminescent charge state in ZnSe:Ni, and Co2+(d7) as the radiative ion in GaP:Co. In GaP-Ni this procedure demonstrates that while Ni2+(d8) may dominate the near-infrared absorption spectrum, the photoluminescence band with zero-phonon line (ZPL) at 5354 cm-1 is attributable to Ni+(d9) as concluded previously by Kaufmann et al. The photoluminescence excitation spectrum of GaP:Ni is shown to contain peaks corresponding to absorption by the inverse of the 2E-2T2 emitting transition of Ni+(d9) and dips corresponding to competing absorption by the 3T1(F)-3T1(P) transition of the Ni2+(d8) charge state which is also present.

Influence of the surface on photoluminescence from indium phosphide crystals

Abstract: The photoluminescence of indium phosphide has been measured on crystals in ultrahigh vacuum and subsequently oxidized in a controlled manner The luminescence intensity can vary by more than an order of magnitude and shows a close correspondence to the known shift of the Fermi level at the surface under oxidation We conclude that the oxidation‐induced surface space charge layer is nonradiative due to the presence of the electric field The band bending and surface charge variation can be estimated quantitatively from the data The influence of surface contamination on Schottky barrier formation is also reported

Laser annealing of glow discharge amorphous silicon

Abstract: Glow discharge amorphous silicon layers have been annealed using a Q-switched ruby laser. The properties of the annealed films were studied as a function of laser energy by means of electron microscopy, photoluminescence and infra-red absorption. The changes in structure, hydrogen content, band-gap and density of states in the annealed layers are discussed. It is found that there are considerable similarities between the amorphous and the annealed material.