Photoluminescence and photoluminescence excitation of AlGaAs/GaAs quantum wells with growth-interrupted heterointerfaces grown by molecular beam epitaxy

We have measured the photoluminescence (PL) and PL excitation (PLE) of AlGaAs/GaAs single quantum wells with growth-interrupted heterointerfaces. PLE shows the small Stokes shifts of less than 1 meV indicating the extremely flat heterointerfaces without microroughness. Photoluminescence spectra show four peaks originating from different monolayer terraces. These peaks exhibit a doublet splitting. We assigned this doublet to free excitons and excitons bound to neutral donors from the strong well width dependence of doublet splitting.     

Microprobe photoluminescence measurement on heteroepitaxial GaAs on Si grown by metalorganic chemical vapor deposition

Microprobe photoluminescence (PL) measurements at 77 K were used to study the effect of the GaAs layer thickness on optical quality and variations in strain in GaAs/Si containing microcracks. PL peak intensities increase with the increase in thickness of GaAs layers and the peak intensity for the 5.5 m GaAs layer was a factor of 20 higher than those for the 1–2 m GaAs layers. Spatial nonuniformities in strain in the vicinity of two microcracks reveal that stress was almost released at the intersection of two microcracks and is maximum half way between two microcracks.On leave from Semiconductor Materials Lab., Korea Institute of Science and Technology (KIST)     

Spectral image cathodoluminescence,photoluminescence and Raman study of GaAs layers grown on Si substrates

GaAs layers grown on Si substrates by the conformal method were investigated by means of Raman, photoluminescence and cathodoluminescence spectroscopies. The combination of these optical techniques allows a better knowledge of the properties of these layers, with special emphasis on the stress distribution and the incorporation of dopants. In particular, samples intentionally doped, with alternate doped and undoped fringes, have been analyzed. The effective incorporation of Si atoms in the GaAs structure to produce n-type layers and the formation of Si complexes are determined by Raman and cathodoluminescence data. The lateral quasi-periodic stress distribution, typically observed in these layers, is shown to affect the Si incorporation.     

Temperature-dependent photoluminescence spectra of GaN epitaxial layer grown on Si(111) substrate

In this paper, the temperature-dependent photoluminescence(PL) properties of Ga N grown on Si(111) substrate are studied. The main emission peaks of Ga N films grown on Si(111) are investigated and compared with those grown on sapphire substrates. The positions of free and bound exciton luminescence peaks, i.e., FX A and D0 X peaks, of Ga N films grown on Si(111) substrates undergo red shifts compared with those grown on sapphire. This is attributed to the fact that the Ga N films grown on sapphire are under the action of compressive stress, while those grown on Si(111) substrate are subjected to tensile stress. Furthermore, the positions of these peaks may be additionally shifted due to different stress conditions in the real sample growth. The emission peaks due to stacking faults are found in Ga N films grown on Si(111) and an S-shaped temperature dependence of PL spectra can be observed, owing to the influence of the quantum well(QW) emission by the localized states near the conduction band gap edge and the temperature-dependent distribution of the photo-generated carriers.     

Photoluminescence spectra of doped GaAs films

We have studied the dependence of the photoluminescence (PL) spectrum on the doping level and the film thickness of n-GaAs thin films, both experimentally and theoretically. It has been shown theoretically that modification of the PL spectrum of p-type material by p-type doping is very small due to the large valence-band hole effective mass. The PL spectrum of n-type material is affected by two factors: (1) the electron concentration which determines the Fermi level in the material; (2) the thickness of the film due to re-absorption of the PL signal. For the n-type GaAs thin films under current investigation, the doping level as well as the film thickness can be very well calibrated by the PL spectrum when the doping level is less than 2×10¹⁸ cm^-3 and the film thickness is in the range of the penetration length of the PL excitation laser. PACS 78.20.-e; 78.55.Cr; 78.66.Fd     

HVPE外延GaN膜中黄带的光致发光激发谱研究

测量了氢化物气相外延方法生长的非特意掺杂和掺碳GaN外延膜的光致发光谱，并在光致发光谱峰位2．25eV(550nm)附近分别测量了光致发光激发谱，对两者进行了比较．从光致发光谱中发现掺碳使黄带明显增强，从光致发光激发谱中看到了掺碳引起的约3．38～2．67eV(367～465nn)范围内的特征激发带．利用CC曲线模型说明了特征激发带和黄带之间的关系，分析了黄带的可能起因．     

Photoluminescence of Si nanocrystals under selective excitation

Photoluminescence of Si nanocrystals passivated by different alkanes (hexane, octane, and tridecane) was studied at room temperature. It is shown that the emission band shape is not affected by the length of the carbon chain in the alkanes used for passivation. A pronounced fine structure of the photoluminescence band consisting of peaks separated by 150-160 meV was observed under resonant excitation. The structure is interpreted by predominant contribution from Si nanocrystal groups with particular stable size/shape existing in addition to the previously reported nanocrystals with “magic” numbers of Si atoms. The contribution of these stable nanocrystals is revealed using selective resonant photoexcitation to the higher energy states in the discrete energy spectrum of such nanocrystals.     

The photoluminescence excitation spectra of multicomponent media

With no restrictions on the value of optical density, we derive an equation that describes the photoluminescence excitation spectra of separate components with overlapping absorption bands in a multicomponent medium. Based on the equation obtained, we propose methods for measuring the ratios of absorption optical densities of the components and quantum yields of their luminescence. The applicability of the proposed methods is demonstrated by measuring the characteristics of coumarin and porphyrin dissolved in different proportions in ethanol. We have also measured the quantum yield and luminescence decay time of the radiationinduced color centers F ₃ ⁺ in the lithium fluoride crystal and calculated probabilities of radiative and nonradiative transitions from the first excited singlet state of these centers.     

The occurrence of sharp exciton-like features in low temperature photoluminescence spectra from MBE grown GaAs

Evidence is presented that a series of sharp exciton-like features 5 to 10 meV below the free exciton feature in the low temperature photoluminescence spectra for MBE grown GaAs can be obtained even for substrate temperatures up to 620°C and for fluxes of As₂, contrary to a recent study. N-type doping reduces or eliminates the exciton-like features. We discuss their origin.     

Photoluminescence and luminescence excitation spectra in ZnSiP2

Summary Measurements of photoluminescence and luminescence excitation spectra of ZnSiP₂ have been performed at 4.2K and two results were obtained. One is the observation of a new sharp emission line at 1.980 eV, due to the bound exciton associated with the pseudodirect gap. The other is the observation of another new series of absorption lines in the luminescence excitation spectrum of an emission line, at 1.984 eV, in addition to those reported previously. These results indicate that in ZnSiP₂ radiative transitions occur at both the indirect and the pseudodirect gaps. Paper presented at the ?V International Conference on Ternary and Multinary Compound?, held in Cagliari, September 14–16, 1982.     

Anomalous temperature dependence of photoluminescence spectra from InAs/GaAs quantum dots grown by formation–dissolution–regrowth method

Two kinds of InAs/GaAs quantum dot(QD) structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the Ga As barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.     

Photoluminescence of HgCdTe nanostructures grown by molecular beam epitaxy on GaAs

Photoluminescence (PL) of HgCdTe-based hetero-epitaxial nanostructures with 50 to 1100 nm-wide potential wells was studied. The nanostructures were grown by molecular beam epitaxy on GaAs substrates. A strong degree of alloy disorder was found in the material, which led to the broadening of the PL spectra and a considerable Stokes shift that could be traced up to temperature T～230 K. Annealing of the structures improved the ordering and led to the increase in the PL intensity. A remarkable feature of the PL was an unexpectedly small decrease of its intensity with temperature increasing from 84 to 300 K. This effect can be related to localization of carriers at potential fluctuations and to the specific character of Auger-type processes in HgCdTe-based nanostructures.     

Structure and photoluminescence properties of ZnS films grown on porous Si substrates

ZnS films were deposited on porous silicon (PS) substrates with different porosities. With the increase of PS substrate porosity, the XRD diffraction peak intensity decreases and the surface morphology of the ZnS films becomes rougher. Voids appear in the films, due to the increased roughness of PS structure. The photoluminescence (PL) spectra of the samples before and after deposition of ZnS were measured to study the effect of substrate porosity on the luminescence properties of ZnS/PS composites. As-prepared PS substrates emit strong red light. The red PL peak of PS after deposition of ZnS shows an obvious blueshift. As PS substrate porosity increases, the trend of blueshift increases. A green emission at about 550 nm was also observed when the porosity of PS increased, which is ascribed to the defect-center luminescence of ZnS. The effect of annealing time on the structural and luminescence properties of ZnS/PS composites were also studied. With the increase of annealing time, the XRD diffraction peak intensity and the self-activated luminescence intensity of ZnS increase, and, the surface morphology of the ZnS films becomes smooth and compact. However, the red emission intensity of PS decreases, which was associated with a redshift. White light emission was obtained by combining the luminescence of ZnS with the luminescence of PS.     

Exciton transitions in photoluminescence spectra of AIAs/GaAs superlattices

Conclusions The studies performed here have shown that the superlattice samples studied exhibit photoluminescence spectra which agree with the Kronig-Penney model, although in calculating the energies of the radiative transitions it is necessary to take into account the binding energy of the excitons,E _B. Due to the exciton—phonon interaction, the 1HH peak breaks up on the long wavelength side into a Poisson distribution. The energy of the LO phonon so determined is 34 meV. Bands due toD ⁰-A ⁰ andD ⁰X transitions, caused by remaining low-level impurities in the GaAs crystals are also observed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 61, Nos. 3–4, pp. 241–245, September–October, 1994.     

Photoluminescence of epitaxial GaAs grown by close space vapor transport method

We report here the first observation of photoluminescence spectra of GaAs epitaxial layers prepared by close space vapor transport method. At 77 K two PL signals were found, the near-band gap transition at 1,51 eV and the other at 1,4 eV. The nature of PL emission lines is discussed in relation with the features of growth method. No simple relation between the growth conditions and concentration of radiative centers was found.     

Erbium photoluminescence excitation spectroscopy in Si: Er epitaxial structures

Excitation spectra of erbium photoluminescence in Si: Er epitaxial structures are studied within a broad pump wavelength range (λ_ex = 780–1500 nm). All the structures studied reveal a fairly strong erbium photoluminescence signal at photon energies substantially smaller than the silicon band-gap width (λ = 1060 nm) with no exciton generation. A possible mechanism of erbium ion excitation in silicon without exciton involvement is discussed.