Showing papers on "Photoluminescence published in 1983"

1.54‐μm luminescence of erbium‐implanted III‐V semiconductors and silicon

Abstract: Well‐resolved sharply structured luminescence spectra at 1.54 μm were observed in erbium‐implanted GaP, GaAs, InP, and Si. The optical transitions occur between the weakly crystal field split spin‐orbit levels, 4I13/2→4I15/2, of Er3+(4f11). Typical spectral linewidths in GaAs are 2 cm−1(0.25 meV) at 6 K and 11 cm−1(1.36 meV) at room temperature.

Energy band‐gap shift with elastic strain in GaxIn1−xP epitaxial layers on (001) GaAs substrates

Abstract: It is demonstrated that the energy band gap in epitaxial layers is changed by biaxial elastic strains which are produced by lattice mismatches in heterostructures. The epitaxial layers used in this work were Gax In1−xP layers grown on (001) GaAs substrates by liquid phase epitaxy. The energy band‐gap shifts were determined by comparing the photoluminescence peak energies of the as‐grown GaxIn1−xP layers with those from free‐standing layers removed from the GaAs substrates. It was experimentally found that the energy band gap shifts linearly with the elastic strain in the layer. Assuming that the lattice mismatch was accommodated only by the elastic distortion, the energy band‐gap shifts in Ga0.5In0.5P alloys were also calculated. The calculated results are 6.0 eV or 4.9×10−12 eV/dyn cm−2 per unit strain or stress, respectively, for the [100] and [010] biaxial elastic stress. These values are in quite good agreement with the experimental results.

Optical and crystallographic properties and impurity incorporation of GaxIn1−xAs (0.44<x<0.49) grown by liquid phase epitaxy, vapor phase epitaxy, and metal organic chemical vapor deposition

Abstract: Optical, crystallographic, and transport properties of nominally undoped n‐type and Zn doped p‐type Gax In1−xAs /InP (0.44

Recombination Enhancement due to Carrier Localization in Quantum Well Structures

Abstract: Picosecond luminescence experiments on $\mathrm{GaAs}/{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum well structures reveal a significant influence of localization on the transition probabilities of photoexcited carriers. The spontaneous lifetime of electrons and holes within the quantum well decreases with well thickness ${L}_{z}$ from 1 ns for ${L}_{z}=14$ nm to 350 ps for ${L}_{z}=5$ nm because of the enhanced recombination due to localization of the carriers.

Effect of Well Size Fluctuation on Photoluminescence Spectrum of AlAs–GaAs Superlattices

Abstract: Photoluminescence spectra for undoped superlattices exhibited smaller half widths compared with those obtained in GaAs bulk crystals. However, both the spectral width and shape were found to be very sensitive to the well size. When the well size is greater than about 80 A, the spectrum at 77 K showed smaller linewidth, which agrees with theoretical results, whereas when the well size is smaller than this, the spectral width increased with decreasing well size. In some cases, additional emission bands appeared in the lower energy side of the main emission peak. These phenomena were interpreted in terms of well size fluctuations.

Growth by molecular beam epitaxy and characterization of high purity GaAs and AlGaAs

Abstract: We report on the growth by molecular beam epitaxy of high‐quality GaAs and AlxGa1−xAs (x≲0.43), and discuss the effect of system parameters on material quality. The highest Hall mobility in GaAs at 77 °K was 144 000 cm2/V sec, and the photoluminescence spectra of undoped layers exhibited a strong free exciton line and a much reduced carbon peak with no carbon‐related defects. A slow growth process at a substrate temperature of 600 °C produced excellent AlxGa1−xAs whose luminescence spectrum showed a distinct excition peak 4 meV wide. This AlxGa1−xAs is compared to layers grown at a faster rate at substrate temperatures of 700 °C.

X‐ray‐induced luminescence in crystalline SiO2

Abstract: The x‐ray‐induced ‘‘blue’’ emission from commercially available, high‐quality synthetic quartz has been studied between 80 and 300 K. Three overlapping bands, each having a different quenching temperature, have been experimentally resolved in the as‐grown crystals. These bands peak at 440, 425, and 380 nm; their half‐widths are 0.64, 0.75, and 0.92 eV; and they thermally quench in the 120–160, 170–210, and 220–270 K regions, respectively. An intense electron irradiation at room temperature or an electrodiffusion (sweep) in a hydrogen atmosphere eliminates the band at 380 nm. Our results suggest that the 380‐nm band arises from recombination of an electron with a hole trapped adjacent to an alkali‐compensated aluminum ion (i.e., an Al–M+ center). The origins of the bands at 440 and 425 nm remain unknown. As an application of these results, a screening test is described which could assist quality control during selection of quartz bars for use in precision frequency control devices.

Magnetic polarons in exciton luminescence of Cd1-xMnxTe

Abstract: Systematic investigations of the photoluminescence spectra of Cd1-xMnxTe mixed crystals were performed for 0

Efficient visible photoluminescence in the binary a‐Si:Hx alloy system

Abstract: We report the photoluminescence (PL) and structural properties of a new class of efficient visible‐light‐emitting semiconductors: low defect density a‐Si:Hx alloys. For films prepared by the (thermal) homogeneous chemical vapor deposition (HOMOCVD) method, new broadband PL develops for x>0.3, reaching a peak emission energy of 2.05 eV for a hydrogen content x=0.66 (40 at. % H). We attribute the wide gaps to the influence of Si–H bonding on the density of states near the valence band edge. We ascribe the new PL process to band‐to‐band recombination from within the alloy band tails. This emission persists at room temperature with an integrated intensity comparable to conventional light‐emitting diode (LED) materials. Qualitatively similar results are obtained for low‐temperature‐deposited rf plasma films prepared from Si2H6, but not from SiH4. We show that a low Si dangling bond concentration is the key factor, for all the different film types, to achieving efficient luminescence.

Growth of Ga0.47In0.53As‐InP quantum wells by low pressure metalorganic chemical vapor deposition

Abstract: We describe the growth of multiquantum well and single quantum well Ga0.47In0.53As‐InP structures by low pressure metalorganic chemical vapor deposition. The multiwell structure consists of 25‐, 50‐, 100‐, and 200‐A quantum wells (Ga0.47In0.53As layers) separated by 500‐A barriers (InP layers). Auger measurements indicate the presence of four distinct wells with abrupt boundaries. Photoluminescence measurements are consistent with the existence of four wells; however, deviations are noted between experimentally determined and theoretically predicted recombination energies. An analogous situation exists for the single (50 and 100 A) quantum well structures. Possible explanations, including variation of well composition, variation of well thickness, and participation of impurities in the recombination process are suggested.

Light transport in planar luminescent solar concentrators: the role of DCM self-absorption.

Abstract: The influence of self-absorption in a 4-dicyano-methylene-2-methyl-6-p-dimethyl amino-styrl-4H-pyran (DCM) doped polymethylmethacrylate (PMMA) optical waveguide on the light transport efficiency has been evaluated. A Monte Carlo technique was used to simulate intermolecular energy transfer and calculate the energy emission profile of an active waveguide. The calculated and measured edge emission profiles were found to be in excellent agreement. The edge emission spectra for various distances of excitation from the edge were used to estimate the DCM self-absorption cross section.

THE GROWTH OF MAGNESIUM-DOPED GaAs BY THE OM-VPE PROCESS

Abstract: Magnesium-doped GaAs has been grown by organometallic vapor phase epitaxy (OM-VPE). Bis (cyclopentadienyl) mag-nesium (Cp2Mg) is used as the organometallic precursor to Mg. The epitaxial layers have been characterized by resis-tivity and Hall measurements, photoluminescence spectro-scopy and optical microscopy. The material is of high electrical and optical quality; controllable doping over the range 1015 to 1019cm-3 is reproducibly attained. The ionization energy of the Mg acceptor is determined to be 30 ± 2.5 meV at 77K. Negligible compensation is observed, consistent with clean thermolysis of the Cp2Mg under growth conditions. GaAs diodes have been fabricated using Mg as the p-dopant and either Se, Si, or Sn as the n-dopant. The diodes show very low leakage currents under reverse bias, even at relatively high doping levels. Degenerately-doped junctions for interconnecting monolithic cascade concentrator solar cells have also been successfully grown, displaying forward conductivities as high as 19 amps V−1 cm-2 at 0.05V forward bias.

GaSb/AlSb multiquantum well structures: molecular beam epitaxial growth and narrow-well photoluminescence

Abstract: Multiquantum well structures of GaSb wells down to 12‐A width, separated by 120‐A AlSb barriers, were grown by molecular beam epitaxy, and their low‐temperature photoluminescence was studied. Even though GaSb should become an indirect‐gap semiconductor for well widths below about 90 A, the direct‐gap luminescence persists to the narrowest wells. The shift of photon energy with well width indicates strong nonparabolicity effects; it is in good agreement with Bastard’s simple model of quantum wells in nonparabolic semiconductors. For wells less than 45 A wide, the direct‐gap luminescence is accompanied by a strong and very broad lower‐energy luminescence peak, which appears to be related to electron accumulation in the X valleys, but the exact mechanism for which is not clear. A two‐electron transition model is proposed.

Silicon doping of MBE-grown GaAs films

Abstract: Two concentration ranges of silicon doping in MBE-grown GaAs films have been investigated in some detail. In lightly doped films, with a free-electron concentration of ≈1016cm−3, low-temperature photoluminescence spectra have been analysed to develop a model to account for spectral features previously attributed to Ge and Si acceptor levels. In heavily doped films, a maximum free-electron concentration of ≈7×1018 cm−3 has been obtained, which is only rather weakly dependent on growth conditions and the nature of the arsenic species (As2 or As4). Transmission electron microscopy has shown that no significant precipitation effects occur when higher Si fluxes are used but there is evidence for autocompensation. The maximum PL intensity (300 K) is found at a lower free electron concentration then with Sn-doped films, and is more sharply peaked, but there is no evidence for an anomalous Moss-Burstein shift.

Kinetics of Radiative Recombinations in GaSe and Influence of Cu doping on the Luminescence Spectra

Abstract: Spontaneous photoluminescence (PL) spectra of Cu-doped and undoped $\ensuremath{\epsilon}$-GaSe have been investigated in the temperature range from 80 to 300 K and at low laser-excitation intensity ($P$) from ${10}^{\ensuremath{-}3}$ to 10 W ${\mathrm{cm}}^{\ensuremath{-}2}$. The main modification of the spectra in doped crystals with respect to those of undoped samples is the appearance of two bands in the extrinsic part of the PL spectrum and centered at 655 and 678 nm, respectively. The luminescence at energies below the excitonic recombinations (extrinsic bands) is enhanced by doping. Also indirect free- and bound-excitonic lines are also strongly influenced by the impurity concentration; in fact, their emission intensity, which depends linearly on $P$ in undoped crystals, shows a quadratic dependence in doped samples. The temperature dependence of the PL spectra gives the thermal activation energy of some extrinsic bands, which results equal the ionization energy of the acceptor levels involved in the extrinsic transitions. A simple kinetic model of the radiative recombination is proposed; it accounts for the experimental data of the excitation intensity dependence of the free- and bound-excitonic lines. This model can also explain the different temperature dependence of the PL intensity of these lines: linear for the free-excitonic emissions, exponential for the bound-excitonic recombinations. Some radiative transitions from donor levels located in the energy gap of GaSe are analyzed and a scheme of donor and acceptor states involved in the PL spectra is proposed.

Influence of radiative recombination on the minority‐carrier transport in direct band‐gap semiconductors

Abstract: When radiative (band to band) lifetimes and nonradiative (multiphonon via flaws) lifetimes become comparable, as is the case for GaAs, the customary diffusion equation for minority carriers under low level injection conditions must be augmented by terms originating from photon transport. Using the generalized van Roosbroeck–Shockley relation between absorption and emission as well as radiative transfer theory, the relevant equations for free carrier transport are derived. Subsequently, it is shown that the influence of the reabsorbed recombination radiation on carrier transport while unimportant at low doping levels becomes important for n‐type GaAs at high doping levels. We also determine the external luminescence flux taking due account of multiple emission and absorption events inside the sample.

Donor discrimination and bound exciton spectra in InP

Abstract: We report detailed studies of the near‐gap photoluminescence (NGPL) of refined vapor phase epitaxial (VPE) InP layers, selected to afford the best chance of resolving structure arising from the small chemical shifts between different donor species. Good general correlation was found between electrical data and the quality of the NGPL spectra in a survey of 50 crystals. In particular, the quality of the D+,X bound exciton (BE) and the ‘‘two‐electron’’ donor satellites (TEDS) of the D0,Xn BE luminescence components correlated with the 77 °K mobility, known to be dominated by ionized impurity scattering. Use of selective excitation with a narrowed line from a dye laser and magnetic fields to obtain spectral components less subject to inhomogeneous broadening is discussed. The magnetic field is most effective in narrowing the TEDS components. The crystal quality, expressed mainly through the total concentration of shallow donors and acceptors, is apparently just inadequate to obtain line narrowing by selective excitation even in the best available crystals of VPE InP. However, selective excitation is still helpful in removing background luminescence and in enhancing luminescence satellites of particular D0, Xn BE components. Inhomogeneous broadenings of the various electronic states are contrasted. Measurements on both the D0, Xn′ TEDS and D+, X show evidence of only a single donor in the few samples with optimum linewidths. The general difference between these NGPL findings and far infra‐red photoconductivity (FIRPC) measurements results from differential incorporation rates for the two most likely inadvertent shallow donor species, Si and S, during the growth of the VPE layers. The energy of the single NGPL donor suggests that it may be Si according to available FIRPC data. Resonantly enhanced Raman scattering (RERS) is observed both amongst the TEDS and through pure electron spin flip transitions. The D+, X and D0,h spectral features are well resolved, and Zeeman spectroscopy is consistent with the D+, X attribution. Approximate electron and hole g values are derived, together with more accurate values of ge from the RERS and of m*e from the TEDS magnetic splittings.

High‐quality ZnSe thin films grown by molecular beam epitaxy

Abstract: High‐quality, nominally undoped, low‐resistivity ZnSe thin films are grown by molecular beam epitaxy (MBE). The MBE ZnSe shows the largest peak intensity ratio of the near‐band‐edge emission to the deep center luminescence even at room temperature compared with other epitaxial techniques, which indicates the smallest concentration of complex defects in the MBE ZnSe. From the temperature dependence of electron mobility for MBE ZnSe, we obtained the mobility value as high as 6.9×103 cm2/Vs. This is the highest value ever obtained in epitaxial ZnSe films and indicates the concentration of isolated charged defects as low as 1×1016 cm−3.

Residual double acceptors in bulk GaAs

Abstract: By using infrared absorption, photoluminescence, and Hall measurements we have observed an additional level associated with a residual acceptor in liquid encapsulated Czochralski GaAs. These results indicate that the defect is a double acceptor with levels 78 and 200 meV above the valence band.

Free excitons in room-temperature photoluminescence of GaAs- Al x Ga 1 − x As multiple quantum wells

Abstract: We report a room-temperature study of the photoluminescence observed from a high-quality, molecular-beam-epitaxy grown GaAs-(AlGa)As multiple-quantum-well structure. The spectrum is dominated by free-exciton emission. This assignment is inferred by the use of photoluminescence excitation spectroscopy.

Optical properties of GaInAs/AlInAs single quantum wells

Abstract: Ga0.47In0.53As/Al0.48In0.52As single quantum wells grown by molecular beam epitaxy have exhibited photoluminescence emission from 9668 A to the 1.55‐μm bulk emission at 4 K. The emission at 9668 A is 0.474 eV above the band gap of GaInAs. The single quantum well (SQW) is 15 A wide which is the narrowest SQW reported in any III‐V compound. The effect of varying the buffer layer of the SQW on the photoluminescence intensity of a 65‐A single quantum well is studied.

Phonon interactions in the tail states of a -Si:H

Abstract: Many experimental data on the 1.4-eV photoluminescence of $a$-Si:H have been interpreted by the assumption of a Stokes shift of up to 0.5 eV. We show that the evidence for a Stokes shift may be satisfactorily explained by a distribution of zero-phonon energies only. This suggests that the radiative states may be rigid and so that there is no evidence for a significant disorder-induced electron-phonon interaction in the tail states of amorphous silicon.

Improved photoluminescence of organometallic vapor phase epitaxial AlGaAs using a new gettering technique on the arsine source

Abstract: Using an aluminum‐gallium‐indium ternary melt for the removal of oxygen and moisture from the arsine source, substantial improvement in the quality of organometallic vapor phase epitaxial AlGaAs can be achieved. The arsine is bubbled through the ternary melt at room temperature prior to its introduction into a low‐pressure reactor. Low‐temperature photoluminescence spectra indicate an improvement in the sharpness of the bound exciton transition after the use of this gettering technique.

Heavy doping of GaAs and AlGaAs with silicon by molecular beam epitaxy

Abstract: Heavy Si doping of GaAs and AlGaAs grown by molecular beam epitaxy has been studied. By using a slow growth rate of 1000 A/h, the electron concentration obtained for GaAs was 1.1×1019 cm−3, which is higher than the previously reported limit of 5×1018 cm−3. The accumulation of excess Si near the surfaces of GaAs and AlGaAs has been identified by secondary ion mass spectroscopy. A Si‐induced 3×2 surface structure has been observed, and the influence of arsenic to gallium flux ratio on the surface morphology is discussed. Photoluminescence spectra of the doped layers are presented.

The nature of photoluminescence from plastically deformed silicon

Abstract: The nature of photoluminescence from plastically deformed silicon crystals is investigated from the dependences of the spectrum and intensity of the luminescence on various parameters. Besides the well established characteristic lines D1 through D4, a broad background component is found to exist in the photon energy range of 0.75 to 1.1 eV. Neither impurities nor clusters of point defects are shown to be responsible for the deformation-induced photoluminescence. Thus, dislocations are concluded to be active as radiative recombination centres. It is shown, however, that dangling bonds are not responsible for the recombination processes. Thus, the reconstructed bonds or severe distortion of the lattice at the dislocation core is thought to contribute to the radiative recombination processes occurring in a plastically deformed silicon crystal. The D1 and D2 lines seem to be related to geometrical kinks on dislocations. Die Ursache der Photolumineszenz von plastisch verformten Siliziumkristallen wird aus der Abhangigkeit des Spektrums und der Intensitat der Lumineszenz von verschiedenen Parametern untersucht. Neben gut bekannten charakteristischen Linien D1 bis D4, wird eine breite Untergrundkomponente im Photonenenergiebereich von 0,75 bis 1,1 eV gefunden. Es wird gezeigt, das weder Storstellen noch Cluster von Punktdefekten fur die deformationsinduzierte Photolumineszenz verantwortlich sind. Deshalb wird angenommen, das Versetzungen als strahlende Rekombinationszentren aktiv sind. Es wird jedoch auch gezeigt, das hangende Bindungen fur den Rekombinationsprozes nicht verantwortlich sind. Deshalb wird angenommen, das die rekonstruierten Bindungen oder schwere Storungen des Gitters am Versetzungskern zum strahlenden Rekombinationsprozes beitragen, der in einem plastisch deformierten Siliziumkristall auftritt. Die D1- und D2-Linien scheinen mit geometrischen Kinks auf den Versetzungen verknupft zu sein.

Photoluminescence and impurity concentration in GaxIn1−xAsyP1−y alloys lattice‐matched to InP

Abstract: The photoluminescence spectra of GaInAsP alloys are examined as a function of impurity concentration at several different temperatures and alloy compositions The photoluminescence linewidth depends on both the impurity concentration and temperature, and our experimental results at 295 °K are described by the empirical relation: ND(ΔE) =91×1011 exp(ΔE/43 ×10−3) cm−3 It is proposed that photoluminescence linewidth can be used for a simple and rapid determination of the impurity concentration for n‐ and p‐type samples whose total impurity concentration lies in the range 1016 cm−3

Photoluminescent and electrical properties of InGaPAs mixed crystals liquid phase epitaxially grown on (100) GaAs

Abstract: The liquid phase epitaxial growth of InGaPAs layers on (100) GaAs is described for growth temperatures of 785 and 815 °C. Photoluminescence (PL) spectra and electron Hall mobility of the layers are investigated as a function of crystal composition. The width of PL spectra measured at 300 K is 40 meV, approximately the same value as that of GaAs, when the energy gap Eg of the layers is 1.9 eV or lower than 1.6 eV. The spectral width is around 80 meV when the energy gap of the layers is around 1.75 eV. The increase in the spectral width is attributed to variation of the local energy gap from analysis of dependence of the PL spectra on temperature and on excitation intensity. The indication that local energy gap varies in layers with Eg around 1.75 eV is consistent with the composition dependence of electron mobility. The mobility shows a sharp dip down to 1000 cm2/Vs around this composition, while it depends on composition only slightly for layers with Eg lower than 1.6 eV. The dip in composition dependence...