Showing papers on "Photoluminescence published in 1982"

Effect of an electric field on the luminescence of GaAs quantum wells

Abstract: Low-temperature photoluminescence (PL) measurements have been performed in narrow GaAs-${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ quantum wells subject to an electric field perpendicular to the well plane. At low fields the PL spectra show two peaks associated, respectively, with exciton and free-electron-to-impurity recombination. With increasing field the PL intensity decreases, with the excitonic structure decreasing at a much faster rate, and becomes completely quenched at a field of a few tens of kV/cm. This is accompanied by a shift in the peak position to lower energies. The results are interpreted as caused by the field-induced separation of carriers and modification of the quantum energies. Variational calculations performed for isolated, finite quantum wells explain qualitatively the experimental observations.

Electrical properties and photoluminescence of Te‐doped GaAs grown by molecular beam epitaxy

Abstract: The application of PbTe as a molecular tellurium source in the growth of n‐type GaAs:Te by molecular beam epitaxy (MBE) has been investigated. We obtained free‐carrier concentrations ranging from 2×1016 to 2×1019 cm−3. In particular in degenerate n‐type material, excellent 77 K Hall mobilities were achieved. Even at high impurity concentrations (≳1018 cm−3), Te was not found to accumulate at the surface if a true Pb‐saturated (n‐type) starting material was used as dopant source. Using low‐temperature photoluminescence measurements, we further studied the influence of the doping concentration on the shift of the Fermi level and on the radiative recombination across the fundamental gap in heavily n‐doped GaAs:Te. Calculations based on the Burstein‐Moss shift and on the band tailing effect, as well as a line shape analysis, were performed for a distinct interpretation of the observed luminescence behavior. At concentrations below 5×1017 electrons cm−3, band‐acceptor transitions involving residual carbon acce...

On the temperature dependence of a.c. conduction in chalcogenide glasses

Abstract: Although it is now fairly well established that defects in amorphous chalcogenide semiconductors are normally charged (D+ and D−), it is demonstrated that neutral defects D0, generated by the reverse reaction of 2D0 → D+ + D−, can be important for a.c. conduction. The contribution to [sgrave](ω, T) from correlated barrier hopping of single polarons exceeds that of bipolarons at high temperatures (T). An expression for [sgrave](ω, T), which includes terms due to electrons hopping between D0 and D+ and holes between D0 and D−, as well as two electrons hopping between D− and D+ (bipolarons), is able to account for all the features observed in chalcogenide glass semiconductors. Effects on the a.c. conductivity of the addition of impurities to chalcogenides are also discussed in terms of the present model. The energy levels and densities of charged defects are estimated for given materials, and these are supported by values deduced from photoluminescence, drift mobility and d.c. conductivity studies.

Compositional dependence of band‐gap energy and conduction‐band effective mass of In1−x−yGaxAlyAs lattice matched to InP

Abstract: The band‐gap energy and the electron effective mass of In1−x−yGaxAlyAs lattice matched to InP have been determined as a function of Al content. From photoluminescence measurements we obtain Eg(eV) = (0.76±0.04)+(1.04±0.10)y+(0.87±0.13)y2. The electron effective mass is determined from the plasma frequencies measured with Raman scattering in n‐type samples. Its compositional dependence is given by m* = (0.0427±0.0015)+(0.0683±0.0007)y.

Optical properties of copper in silicon: Excitons bound to isoelectronic copper pairs

Abstract: Copper doping of silicon crystals results in an intense emission at 1.014 eV. The photoluminescence spectrum exhibits a characteristic structure consisting of a narrow nophonon line and equispaced lower-energy resonant-mode phonon replicas. The typical phonon energy is 7.0 meV. We observe isotope shifts of the lines which conclusively show that copper is incorporated in the luminescent defect. Combination with the observed quadratic dependence of the emission intensity on copper concentration leads us to suggest copper pairs as recombination centers. The symmetry of the pair as determined from uniaxial stress and Zeeman data is that of a $〈111〉$ configuration. The no-phonon line structure and the splitting in external fields indicate an exciton localized at an isoelectronic trap. The exciton is discussed in terms of an isoelectronic donor combining the present data with recent deep-level transient-spectroscopy results.

Low temperature photoluminescence of lightly Si-doped and undoped MBE GaAs

Abstract: A semiquantitative low temperature (~4 K) photoluminescence technique has been used to estimate the residual carbon concentration in MBE GaAs to be ~2 × 1014 cm−3 . This value agrees well with the total compensating acceptor concentration calculated from electrical measurements and thus confirms that carbon is the dominant residual acceptor in MBE GaAs. In high purity MBE GaAs films grown at substrate temperatures between 545°C and 625°C a band of at least nine luminescence peaks is observed in the 1.471 eV to 1.491 eV spectral region. These peaks can be correlated with the most prominent "defect-induced" bound exciton peaks in the 1.504 eV to 1.511 eV spectral region and their transition energies follow the empirical relation $$hv_{C_{As}^o ,X} - hv_{d,X} = 0.38[hv_{e,C_{As}^o } - hv_{e,d} ].$$ This suggests that the luminescence in these two spectral regions have a common origin at a set of “defect-complexes” which involve carbon impurities.

Spectrum and polarization of hot-electron photoluminescence in semiconductors

Abstract: Experimental and theoretical research on the recombination photoluminescence of free hot electrons in semiconductors (primarily GaAs) is reviewed. The polarization characteristics are discussed. These characteristics reflect, in particular, a momentum alignment of the electrons by linearly polarized light and an effect of a ripple in the constant-energy surfaces in the valence band. The dependence of the linear polarization on the spectrum is discussed in connection with various mechanisms for the energy relaxation of the hot electrons. The depolarization of the hot-electron photoluminescence in a magnetic field is discussed. A procedure is discussed for determining the energy relaxation times and the scale times for intervalley transitions through an analysis of depolarization curves. The energy distribution of the hot electrons is found from the hot-electron photoluminescence spectrum. The recombination luminescence of hot holes is discussed. These holes appear when the semiconductor is illuminated in the spin-split-off subband.

Crystal orientation dependence of silicon autocompensation in molecular beam epitaxial gallium arsenide

Abstract: Silicon‐doped GaAs has been grown simultaneously on (100), (110), and (111)B oriented GaAs substrates by molecular beam epitaxy. For constant Si, Ga, and As4 fluxes the surface morphology of the (110) and (111)B faces degraded with increasing substrate temperature above ∼500 °C. (100) films had an n‐type free‐electron concentration of 5×1016 cm−3 independent of substrate temperature. Films on (110) substrates were p type when grown above ∼550 °C and n type below ∼550 °C whereas (111)B films were highly resisitive under most growth conditions. Low‐temperature (4 K) photoluminescence showed good correlation between the Si acceptor peak heights and the compensation ratios derived from electrical measurements.

An investigation of the deep level photoluminescence spectra of InP(Mn), InP(Fe), and of undoped InP

Abstract: Deep level photoluminescence bands related to Mn and Fe in InP are investigated. In InP(Mn) a strong broad band peaking at 1.15 eV and with phonon structure at 1.184, 1.145, and 1.107 eV is observed. A broad band peaking at 1.10 eV with weak phonon structure at 1.135, 1.098, and 1.062 eV is observed in InP(Fe). Several undoped InP crystals also reveal a band identical to that seen in InP(Mn) suggesting that Mn may be an inadvertent impurity. In these undoped samples and also in InP(Cr) the intensity of this band is greatly enhanced after thermal annealing (750 °C), suggesting that Mn may be diffusing to the surface. Mn has been previously reported to behave in this way in GaAs. Other unidentified deep level photoluminescence features in undoped material are also observed at 0.765 and 1.284 eV. Fe is detected as an inadvertent impurity in some undoped samples from studying the Fe2+(5T2−5E) internal transition.

Extrinsic layer at AlxGa1−xAs‐GaAs interfaces

Abstract: Photoluminescence studies of GaAs‐AlxGa1−xAs heterostructures grown by molecular beam epitaxy (MBE) which contain one and two GaAs quantum wells suggest that in some of the samples the first well grown usually exhibits a ’’rough’’ (6 A≲δL≲15 A) first interface and an acceptorlike luminescing impurity in the first few tens of angstroms of GaAs grown. The luminescence may arise from carbon which accumulates on the AlxGa1−xAs ‐vacuum interface during growth and is then deposited in the first few unit cells of GaAs. The phenomenon discussed may be relevant to the problem of growing high electron mobility field‐effect transistor heterostructures by MBE with GaAs on the top.

Anomalous photoelectronic processes in SrTi O 3

Abstract: The photoelectronic properties of nominally pure SrTi${\mathrm{O}}_{3}$ single crystals were studied in detail. A sharp narrow peak near the fundamental absorption edge was observed in both photoconductivity and photoluminescence excitation spectra, although it was not detected in the absorption spectrum. The temperature dependence of the half-width of this anomalous peak was found to have a behavior similar to that of the absorption bands of $F$ centers in alkali halides. The photocurrent associated with this peak was found to depend strongly on temperature. The photoconductive gain at 10 K was estimated to be at least 8\ifmmode\times\else\texttimes\fi{}${10}^{5}$. Marked thermal and optical quenching of the photocurrent were measured. In addition, a supralinearity phenomenon, by which the photocurrent varies as the 5th power of the light intensity, was observed. On the basis of the results of the varied experiments designed to elucidate the nature of the transition responsible for the anomalous peak, we have reasonably established that it is due to the descrete transition by which an electron is raised from the ground state of a highly localized sensitizing center to an excited state located in the conduction band; subsequently a free electron is produced by the process of autoionization. It has been shown that there is a strong correlation between photoconductivity and photoluminescence. The infrared emission, attributed to the electronic transition within a ${\mathrm{Cr}}^{3+}$ ion, can be excited by either the anomalous-peak radiation or band-to-band radiation; however, the visible emission, ascribed to the recombination of a free hole with a level below the conduction band, can be excited only by band-to-band radiation. These and other photoluminescence results are discussed in terms of charge-transfer processes and an association model involving the ${\mathrm{Cr}}^{3+}$ ion and the highly localized center responsible for the anomalous peak.

Photoluminescence identification of ∼77‐meV deep acceptor in GaAs

Abstract: A study of the photoluminescence emission band at ∼1.44 eV present in GaAs has been made at temperatures between 2–300 K. Changes in photoluminescence excitation intensity, emission energy, and emission intensity as a function of temperature lead to the identification of a 77±2‐meV deep acceptor. The temperature dependence of the emission‐peak energy follows Eagles’ model for the free electron‐neutral acceptor transition. The origin of the acceptor is discussed on the basis of the presence of a high concentration of arsenic vacancies.

Evidence of intrinsic double acceptor in GaAs

Abstract: Acceptors present in undoped p‐type conducting GaAs have been studied with photoluminescence, temperature‐dependent Hall measurements, deep level transient spectroscopy, and spark source mass spectrometry. It is shown that p‐type conduction is due to presence of the shallow acceptor CAs and the cation antisite double acceptor GaAs. The first and second ionization energies determined for GaAs are 77 and 230 meV from the valence‐band edge.

Photoluminescence of Hydrogenated Amorphous Carbon Films

Abstract: Hydrogenated amorphous carbon films have been prepared by the glow-discharge decomposition of ethylene gas. The film shows wide properties depending on gas temperature during discharge. With increasing gas temperature from 200 to 350°C, hydrogen content in the film decreases, and thereby the optical gap decreases from 2.6 to 1.2 eV and the ESR spin density increases from ~1017 to ~1019 cm-3. The photoluminescence spectrum consists of two emission bands. The peak energy of the main band shifts from 1.93 to 1.64 eV as the gas temperature increases. Emission intensity is very insensitive to measurement temperature.

Deep radiative levels in InP

Abstract: Results of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by the bulk and epitaxial techniques are reported. In order to understand the origin of the photoluminescence (PL) spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the liquid phase epitaxy (LPE) wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cd diffused bulk samples. Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donorlike level related to the P vacancy. Bands at 1.21 and 1.14 eV appear to be due to emission to native acceptor levels associated with the In vacancy. The 1.08‐eV band is attributed to emission to a complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these bands and residual impurities is discussed.

Photoluminescence dead layer in p‐type InP

Abstract: Photoluminescence intensity of p‐type InP Schottky diodes was measured as a function of excitation wavelength for several values of applied bias. The intensity increases with penetration depth of the excitation radiation and is quantitatively consistent with a nonradiating surface dead layer. The dead‐layer thickness is somewhat less than the diode depletion width, but has the same functional dependence on applied bias.

Characterization of Nonuniformity in Semi-Insulating LEC GaAs by Photoluminescence Spectroscopy

Abstract: Nonuniform distributions of deep levels in semi-insulating (S.I.) LEC GaAs are investigated by photoluminescence measurements at 4.2 K. Two emission bands at 0.65 and 0.80 eV always appear in S.I. crystals. The intensity profile for the 0.65–eV band is U- or W-shaped along a wafer diameter, corresponding to the etch-pit-density (EPD) profile, while that for the 0.80–eV band shows an inverse profile with respect to the EPD profile. This profile is strong evidence for the idea that the 0.65–eV band is associated with the main electron trap (EL2) present in S.I. crystals. The origin of the 0.80–eV band is considered to be the microdefects generated dominantly in the low-dislocation-density region.

Ga-Doped ZnSe Grown by Molecular Beam Epitaxy for Blue Light Emitting Diodes

Abstract: The MBE-grown ZnSe layer on GaAs (100) with an optimum doping of Ga is found to exhibit an extremely low resistivity and a strong blue near-band-gap photoluminescence (PL) emission (~4610 A) without any deep broad emissions at room temperature. At lower Ga-cell temperatures, the carrier concentration and blue PL emission intensity increases significantly owing to an increase in substitutional Ga atoms acting as donors. At higher Ga-cell temperatures, an excess incorporation of Ga results in a reduction of carrier concentration, a decrease in blue PL emission, and a marked increase in deep broad emission (~5900 A).

Chemical vapor deposition and characterization of phosphorus nitride (P3N5) gate insulators for InP metal‐insulator‐semiconductor devices

Abstract: A new gate insulating film consisting of P3N5 was formed on an InP surface by a new chemical vapor deposition (CVD) technique. A suitable combination of reagents (PH3 and NH3) made P3N5 CVD feasible in an ambient free from oxygen and having excess phosphorus pressure. The new insulator revealed ohmic conduction with a resistivity as high as 104Ω cm. The breakdown field intensity increased up to 107V/cm at room temperature. The low frequency dielectric constant was 3.7 e0. A very minor hysteresis was seen in the capacitance‐voltage curves measured on P3N5‐ InP metal‐insulator‐semiconductor diode. The interface state density was reduced to 1012/cm2eV at an energy near the conduction band edge. Photoluminescence spectra were measured before and after CVD to determine the surface passivation effect.

Conduction mechanism in low-resistivity n-type ZnSe prepared by organometallic chemical vapor deposition

Abstract: n‐type ZnSe layers with a room‐temperature resistivity of less than 0.05 Ω cm and mobilities of ∼400 cm2/(V sec) have been grown on (100) GaAs by organometallic chemical vapor deposition (OM‐CVD), using triethylaluminum as a dopant. No further treatment after the layer growth is necessary in order to achieve the high electrical conductivity. An analysis of the low‐temperature electrical transport data and of the photoluminescence data, however, suggests that the physical properties of the layers differ from those of ZnSe prepared by other methods. Charge transport occurs via impurity‐band conduction in the more heavily doped layers and via thermally activated hopping in the more lightly doped layers rather than via thermally activated extrinsic conductivity. The degree of compensation of donors is larger than 0.5. The exact nature of the compensating centers in the material prepared by OM‐CVD is uncertain at this point, although the photoluminescence data suggest the presence of Al‐VZn complexes.

High quality InP grown by molecular beam epitaxy

Abstract: We report the first high quality InP grown by molecular beam epitaxy (MBE). The undoped InP layers are n type with residual impurity concentrations ∼5×1014–∼5×1015 cm−3. Fine structure attributed to polariton, neutral donor‐exciton (D0–X), neutral donor–hole (D0−h), neutral acceptor–exciton (A0–X) transitions at the exciton edge and neutral donor‐neutral accepton (D0–A0) transitions are clearly resolved in the low‐temperature (5 K) photoluminescence spectra with a linewidth of <1 meV for D0–X as has been observed with high‐purity InP layers grown by other methods. Elemental In and P (red phosphorus) were used as the primary molecular beam sources. The growth temperature has a very significant effect on the quality of the InP layers. The advanced design of the present MBE system employed for growing III‐V compound semiconductors containing P from elemental red phosphorus is also described.

Interference effects in luminescence studies of thin films

Abstract: Interference effects, including multiple-beam and wide-angle, associated with luminescence from within a thin film are described. A simple geometrical model is used to calculate the s- and p-polarized luminescent light assuming electric-dipole radiation. The luminescence exhibits fringes when measured both as a function of the film thickness and as a function of the wavelength of the light. In the latter case the fringes can also show a beating effect. The model is applied to several experimental examples of cathodoluminescence in SiO(2) and an example of photoluminescence in a-Si.

Nitrogen as shallow acceptor in ZnSe grown by organometallic chemical vapor deposition

Abstract: Thin layers of ZnSe were grown on (100) GaAs substrates by organometallic chemical vapor deposition in the presence of ammonia with the intent to incorporate nitrogen as a group V acceptor. Low‐temperature photoluminescence studies confirm that nitrogen is indeed incorporated as a shallow impurity with an activation energy of between ∼110 meV. ZnSe grown in the presence of phosphine gas, on the other hand, exhibits a photoluminescence spectrum characteristic of deep impurity level. A comparison of these results with other published data suggests that both N and P are incorporated as substitutional acceptors replacing Se.