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We report measurements of hot-carrier photoluminescence from GaAs V-groove quantum wires. CW spectra reveal distinct one-dimensional subbands: at low excitation density recombination from laterally confined nv=1 states is dominant, which shows that carriers relax efficiently to the lowest subband; nv=2 and 3 recombination becomes pronounced at higher temperature and density, which indicates inhibited relaxation, possibly due to band filling. Time-resolved photoluminescence measurements at 10 K show a rise time of approximately 100 ps, which is due to energy relaxation. At later times the intensity of the nv=1 line shows a monotonic decay at low carrier density, but there is a nv pronounced plateau at high density that extends for approximately 200 ps. These results provide clear evidence of carrier relaxation and band filling in quantum wires.

Trapping into the active region is one of the most important design considerations in quantum well lasers. This process becomes crucial for the operation of quantum wire devices since the very small active volume demands strong coupling to the external region, otherwise trapping is greatly inhibited. We report the first measurements of electron trapping from extended three-dimensional (3D) states into one-dimensional (ID) states of a semiconductor quantum wire structure. Our joint theoretical and experimental investigation shows that the trapping time is extremely fast, ~10 ps.

Note: Ecole polytech fed lausanne,dept micro & optoelectr,ch-1015 lausanne,switzerland. Ryan, JF, UNIV OXFORD,CLARENDON LAB,DEPT PHYS,PARKS RD,OXFORD OX1 3PU,ENGLAND. ISI Document Delivery No.: TZ177 Cited References: ANTHONY CJ, 1994, SEMICOND SCI TECH, V9, P36 BLOM PWM, 1992, PHYS REV B, V47, P2027 CHRISTEN J, 1992, APPL PHYS LETT, V61, P67 CHRISTEN J, 1992, SURF SCI, V267, P257 CITRIN DS, 1993, IEEE J QUANTUM ELECT, V29, P97 DEVEAUD B, 1988, APPL PHYS LETT, V52, P1886 KAPON E, 1989, PHYS REV LETT, V63, P430 MACIEL AC, 1995, APPL PHYS LETT, V66, P3039 ROTA L, 1993, P INT WORKSH COMP EL, P236 ROTA L, 1995, PHYS REV B, V52, P5183 TIWARI S, 1994, APPL PHYS LETT, V64, P3536 NR 11 TC 30 PU AMERICAN PHYSICAL SOC PI COLLEGE PK PA ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA SN 0163-1829 Reference LOEQ-ARTICLE-1996-025doi:10.1103/PhysRevB.53.R4225View record in Web of Science Record created on 2007-08-31, modified on 2017-05-12

We report a clear evidence of bistability in the current–voltage characteristics of p‐i‐n heterostructures containing InGaAs V‐shaped quantum wires. The observed phenomenon is explained in the framework of a single carrier transport model in which the quantum wires act like traps for the vertical current. The charge trapping phenomenon is indeed demonstrated by temperature‐dependent photocurrent experiments.

The refractive indices of AlxGa1−xAs epitaxial layers (0.176⩽x⩽1) are accurately determined below the band gap to wavelengths, λ

To identify the defects responsible for anomalous electronic properties at the molecular-beam-epitaxy regrown interface, the interfaces of Si-doped GaAs epitaxial layers (n=7×1016 cm−3) have been investigated. A significant reduction of the carrier concentration in a large region around the regrown interfaces has been observed by capacitance–voltage measurement. Photoluminescence spectra measured at different etching depths below the sample surface show that the intensity of the emissions associated with carbon acceptors and As vacancy–carbon acceptor complexes strongly increases in the interface region. The carbon-related emission line is absent in the photoluminescence spectra of the sample without regrown interface. The carrier concentration profiles obtained by capacitance–voltage measurements fit well that calculated numerically with the assumption that a high concentration of carbon is present at the interface. These results indicate that carbon and As vacancies are main defects responsible for the carrier depletion at the regrown interface. This carrier depletion is believed to be due to the direct compensation of Si donors by carbon acceptors. On the other hand, a high concentration of As vacancies at the interface is favorable for the formation of As vacancy-oxygen complexes that may act as deep-level electron traps.

Near infrared Brillouin scattering and high resolution x-ray diffraction is used for a precise determination of the elastic constants and the relaxed lattice parameters of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ epitaxial layers $(0.1l~xl~1.0).$ The composition of the layers is specified by inductively coupled plasma atomic emission spectroscopy, photoluminescence, and Raman spectroscopy. For the elastic constants we get a composition independent value of $118.9\ifmmode\pm\else\textpm\fi{}0.7 \mathrm{GPa}$ for ${\mathrm{C}}_{11},$ a nonlinear increase in ${\mathrm{C}}_{12}$ and a linear decrease in ${\mathrm{C}}_{44}$ with increasing Al composition. The Poisson ratio shows a linear increase for $xl0.8$ and a downward bowing for higher Al concentrations to the AlAs value of $\ensuremath{\nu}=0.325\ifmmode\pm\else\textpm\fi{}0.004.$ The effect of lattice mismatch induced strain on the elastic properties is investigated on free standing epitaxial layers. The trend in ionicity from the GaAs to the AlAs bonds are deduced from phenomenological expressions for the bond-bending and bond-stretching forces which are calculated from the elastic constants. The lattice parameters of the unstrained crystals are obtained from the measured full metric of the tetragonally strained layers and the Poisson ratios. The combined results of Brillouin scattering, x-ray diffraction, and compositional analysis confirm the deviation of the ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ lattice parameter from Vegard's law, and provides the first direct and accurate determination of the quadratic bowing parameter.

The effects of background n- and p-type doping on Zn diffusion in GaAs/AlGaAs multilayered structures are investigated by secondary-ion-mass spectrometry and photoluminescence measurements. Zn diffusions are performed at 575 degrees C into Si-doped, Be-doped, and Si/Be-codoped identical GaAs/Al0.2Ga0.8As multiple-quantum-well structures. The results obtained by secondary-ion-mass spectrometry show that the Zn diffusion induces an enhancement of Be out-diffusion and the disordering of all structures. The effective Zn diffusivity and the disordering rate are increased by Be doping and reduced by Si doping. Photoluminescence measurements give information about the reactions of different point defects during the diffusion process. Before Zn diffusion, the Si-doped structures contain a high concentration of column-III vacancies, whereas As vacancies are the dominant defects in the Be-doped structures. After Zn diffusion, we observe a reduction of column-III vacancy concentration in Si-doped structures and an increase of column-III interstitial concentration in Be-doped structures. A model based on the "kick-out" mechanism of Zn diffusion is proposed to explain our observations. The supersaturation of column-III interstitials behind the Zn diffusion front is responsible for the enhancements of Al-Ga interdiffusion and Be out-diffusion. The effective Zn diffusivity is controlled by the background donor or acceptor concentration ahead of the Zn diffusion front and by the concentration of column-III interstitials behind the Zn diffusion front. For Be-doped structures, the increase in the background acceptor concentration and the supersaturation of column-III interstitials in the Zn-diffused region results in an enhancement of the Zn diffusivity. For Si-doped structures, the effective Zn diffusivity decreases with increasing background donor concentration. Moreover, the concentrations of column-III interstitials and column-III vacancies in the Zn-diffused region are reduced due to their mutual annihilation, leading to a retardation of Zn diffusion. (C) 1999 American Institute of Physics. [S0021-8979(99)05913-7].

Strong evidence for amphoteric native defect reactions is obtained by photoluminescence analysis of Si-doped GaAs samples (n≈1.5×1018 cm−3) annealed under different conditions. Annealing in excess As4 vapor creates a large concentration of Ga vacancies, making possible the transformation of this defect into an As vacancy and an As antisite defect. Similarly, As vacancies generated at high concentration during annealing under Ga-rich conditions are transformed into Ga vacancies and Ga antisite defects. Photoluminescence intensities associated with the corresponding defects are in qualitative agreement with the predictions of the mass action law applied to the amphoteric native defect reactions.

Investigating the ternary InxGa1−xAs alloy (x ∼ 12%) by cross-sectional scanning tunneling microscopy, we find that on the UHV-cleaved (110) surface the In distribution in both the surface and the first subsurface layer can be atomically resolved in the empty- and filled-state images, respectively. This is found to be mostly a geometric effect due to the larger size of the In. We apply this method to study the incorporation of In during the growth of In0.12Ga0.88As quantum wires on nonplanar substrates. Strong In segregation in the growth direction is seen in the structure, and we compare the incorporation profiles across the quantum wire and a planar quantum well. No In clustering beyond the statistical expectation is observed.

Capacitance‐voltage (C‐V) analysis of high quality MBE grown quantum well samples shows that carrier distributions are averaged over the scale of the Debye length. This averaging process results in strongly temperature dependent C‐V‐deduced doping distributions that can be very different from the actual ones. The doping distribution of the structure is obtained by fitting numerically simulated curves to the measured C‐V curves and doping profiles, respectively. Although the calculations do not take quantum size effects into account they show good agreement with the measured data.

Photoluminescence (PL) and electroluminescence (EL) measurement of GaAs/AlGaAs quantum wires (QWR) located in the active region of a p-i-n junction are reported. The samples are fabricated by molecular-beam epitaxial growth on V-grooved substrates. Good control of the interface, defect density and doping profile have been achieved. Homogeneous current injection into the quantum wires is achieved with efficiencies comparable to current injection into a quantum well control sample. PL with and without an applied voltage across the junction was measured at 86 K and 300 K for different excitation densities. Peaks appearing with an applied voltage correspond to the active-region QWR transitions and are also observed on the EL spectra measured at 120 K and at 300 K. Clear evidence of 1D confinement is observed in both PL and EL spectra. They show a one-dimensional splitting of about 24 meV and a saturation of the ground state at high excitation density. The polarisation of the PL and EL is in good agreement with the expected anisotropy of the 1D matrix elements.

In cathodoluminescence spectra of high-quality GaAs/AlxGa1-xAs multi quantum wells (well thicknesses and barrier composition in the range 2.7 nm

We have determined the main parameters of the quasi-one-dimensional excitons confined in GaAs V-shaped quantum wires, namely exciton Bohr radius and binding energy, by two-photon absorption and magnetoluminescence experiments. The experimental results are in excellent agreement with our calculations, based on realistic wave functions for the actual wire geometry.

We have investigated the optical properties of excitons in GaAs quantum wires grown on nonplanar patterned substrates (V-shaped quantum wires) by photoluminescence and magnetophotoluminescence. The experimentally observed transitions are in agreement with the theoretical evaluation of the quantized energy levels based on TEM measurements. The clear evidence of the ${\mathit{n}}_{\mathit{y}}$=1 and 2 excitonic recombination in the photoluminescence spectra is exploited to directly measure the anisotropy of the optical matrix elements.

In a recent paper we measured the lateral hole diffusion in a GaAs/AlGaAs single quantum well (SQW) by a novel method. At helium temperature, we estimate a lateral hole diffusion length in the QW of 1.5 mum. However, the assumption that diffusion takes place mainly in the, SQW needs to be checked, as the measured diffusion length is the result of two competing processes: (i) hole diffusion in the SQW plane itself and (ii) hole diffusion in the barrier followed by recombination in the SQW. We present here a comparison between the lateral hole distribution in the SQW and in the AlGaAs barrier. First, we estimate the hole diffusion length in the barrier fitting experimental cathodoluminescence linescans on simulated ones. Second, using the measured diffusion lengths in the QW plane and in the bulk barrier and modeling the carrier transport, we deduce the lateral hole distribution in both layers. It is found that even for very large barriers (1.2 mum), the hole diffusion in the barrier contributes less than 0.1% of the total lateral hole diffusion. The lateral transport is mainly carried by holes in the QW (2D diffusion) due to their confinement in the well.

The cathodoluminescence mode of the scanning electron microscope is used for the first time to investigate the lateral dependence of the electron-hole pair generation by the electron beam of the scanning electron microscope m semiconducting material. A multiple-quantum-well structure acts as a detector to measure the relative number of generated carriers by their radiative recombination. The method, which avoids the effect of carrier diffusion, enhances the resolution of the measurement to 50 nm and should prove a help for the quantitative interpretation of cathodoluminescence evaluations.

The requirements on optical links for transferring analog and digital signals from the detector front-ends to the readout electronics at future high-luminosity colliders are reviewed. The advantages of external modulation techniques are discussed. An outline is given of the the R&D programme recently started at CERN by a collaboration involving high-energy physics institutes, optoelectronics research laboratories and industry, in order to develop electro-optic intensity modulator arrays, particularly for analogue applications, and to investigate the feasibility of volume production. The design of multichannel demonstrators in lithium niobate and III-V semiconductor technology is described. Preliminary results of the performance measurements are presented.

After Zn diffusion into Si-doped GaAs (n almost-equal-to 1.5 X 10(18) cm-3), the Zn-diffused samples are annealed under different conditions: (i) in vacuum, (ii) in arsenic vapor, and (iii) with a Si3N4 mask capping the sample surface. The Zn concentration profiles obtained by secondary-ion-mass spectroscopy and the photoluminescence (PL) spectra taken at different depths below the sample surface are studied in detail. After annealing in vacuum, the steep (p+-n) Zn diffusion front advances into the bulk. We observe that the intensity ratio between the Si donor-gallium vacancy complex (Si(Ga)-V(Ga)) related emission band and the band-to-band (e-h) transition is enhanced in the region ahead of the Zn diffusion front. In contrast, Zn atoms diffuse deeper into the bulk of the samples annealed in arsenic vapor with or without capping layer. These samples show the kink-and-tail (p+-p-n) Zn concentration profiles with a decrease in the intensity ratio around the tail region. The analysis of the PL data suggest a supersaturation of gallium vacancies ahead of the diffusion front of the sample annealed in vacuum and an undersaturation of this defect around the tail region of the samples annealed in As vapor. Our results underline the important role of the nonequilibrium of the defect concentration during the postdiffusion annealing, which permits explanation of the anomalous double profile of Zn by the interstitial-substitutional mechanism.

The elastic constant C11 of AlxGa1−xAs is determined by near infrared Brillouin scattering. It shows a clear linear decrease with increasing Al concentration. This is in qualitative agreement with trends observed in elastic constants from many different binary semiconductor compounds. The observed linear dependence of C11 extrapolates perfectly to the value for GaAs taken from ultrasonic sound velocity measurements. The linear decrease found is proposed to be dominated by the change in ionicity of the valence bonds in AlxGa1−xAs.

The photoluminescence (PL) peak positions of the ground state heavy and light‐hole excitons on high‐quality Molecular Beam Epitaxy grown GaAs/AlxGa1−xAs (x=0.3 and 1) multiquantum‐well structures have been experimentally determined in the temperature range 4.2≤T≤340 K. Using these values and the well‐known low‐temperature energy of the GaAs Γ8V‐Γ6C gap [EgΓ(GaAs,T=0 K)=1.5192 eV], we propose the temperature dependence to be EgΓ(GaAs,T)= 1.5192+5.16×10−5×T−1.99×10−6×T2 +2.60×10−9×T3 (EgΓ in eV). The nearly linear variation of EgΓ(GaAs,T) versus the temperature in the range 170 K≤T≤340 K can be approximated by a coefficient (dEgΓ/dT)=−4.4×10−4 eV/K, in excellent agreement with theoretical predictions.

The optical properties of low pressure metal organic vapor deposition grown GaAs/AlxGa1-xAs (x = 0.5) single quantum well structures (SQW) with grown-in dislocations (GD) were studied by low temperature cathodoluminescence (CL) and photoluminescence (PL). High luminescence efficiency around the GD was observed and attributed to impurity decoration. CL spectra show a region surrounding the GD that consists of Si impurities and native defects in the SQW and barrier layers. The diameter of this region was found to be in the order of 1 mum using spectrally resolved CL micrographs.

GaAs/AlxGa1−xAs multiple‐quantum‐well (MQW) structures with identical well thicknesses but with different Al contents x in the barrier (x≊0.1, 0.2, 0.45, and 1) were grown by molecular‐beam epitaxy to study the impurity‐induced disordering mechanism. The disordering of the structures is observed directly by transmission electron microscopy on cleaved wedges of the sample, by the secondary electron imaging mode of scanning electron microscopy, and by secondary‐ion‐mass spectroscopy after Zn diffusions at 575 °C during different times (1, 4, 9, and 16 h). The results show that the totally and partially disordered regions are always behind the Zn diffusion front. The partially disordered extent depends on x. As x increases, the disordering rate increases due to the increase in Zn diffusivity. The effect of high Zn concentration is investigated by photoluminescence and by Raman scattering measurements. The systematical analysis of the photoluminescence spectra of the MQW structures diffused for different time...

A strong anisotropy of the photoluminescence emission of high quality quantum wells parallel and orthogonal to the growth axis is demonstrated. This shows up as a series of impressively sharp photoluminescence lines (≈ 0.1 meV) which are only seen on the cleaved facet of growth interrupted single quantum wells, i.e. orthogonal to the growth axis. It is explained in terms of coupled exciton-photon modes called polaritons, which enhance the coupling to excitons in large QW areas with smooth interfaces. The different emission lines are attributed to distinct areas in the quantum well. Polariton effects for excitons in such finite areas are discussed by a semiclassical theory.

The authors have studied AlGaAs grown by molecular beam epitaxy (MBE) before and after post-growth hydrogen plasma treatment by means of temperature-dependent photoluminescence (PL), capacitance-voltage (C/V), and electron-beam-induced current (EBIC) analysis. The excitonic and extrinsic luminescence features of n-type AlGaAs samples subjected to a hydrogen plasma reveal the neutralization effect of vacancies and shallow acceptors. The hydrogen incorporation provides an increase of the non-radiative lifetime of the minority carriers. This behavior was checked by investigations of the minority carrier diffusion and of the quantum yield, which increase due to the hydrogen incorporation. The increase of the non-radiative lifetime is probably caused by the passivation of non-radiative recombination channels involving vacancies.

We characterize an AlGaAs rib waveguide using a structure based on a third-order Bragg reflector fabricated by electron-beam lithography. The grating forms a resonant cavity with the sample's uncoated output facet, and we observe a Fabry-Perot etalon behavior superimposed on the Bragg reflector characteristics. We present transmitted intensity measurements as a function of wavelength and temperature. We derive results for waveguide refractive-index profile, loss coefficient, group effective index, effective-index wavelength dispersion, and effective-index temperature dispersion. An auxiliary prism on top of the grating allows us to couple light out of the waveguide into the air. Angular measurements of the outcoupled orders at different wavelengths confirm the wavelength dispersion measurements made on the Fabry-Perot etalon formed by the grating and the cleaved mirror.

Low-loss (1.4-cm(-1)) single-mode rib waveguides in Al(x)Ga(1-x)As heterostructures are fabricated by liquid phase epitaxy, double anodization, and photolithographic techniques. Switching of optical channels between adjacent waveguides is accomplished with directional coupler switches controlled with electrodes laid over an isolating dielectric, making a metal-oxide-semiconductor (MOS) configuration. Complete switching is achieved with20 V applied to a stepped Deltabetareversal electrode configuration. A 2 x 4 switching matrix with low-loss lateral offsets of the waveguides is demonstrated. By laying out several optical switching and guiding experiments within a 128-mum stripe, we show that independent optical circuits can be packed with adequate optical isolation using centerline separations approximately 10 microm.

GaAs/AlxGa1-xAs multiple-quantum-well structures with identical well thicknesses (almost-equal-to 119 angstrom) but with different Al contents x in the barrier (x almost-equal-to 0. 1, 0.2, 0.45, and 1) were grown by molecular-beam epitaxy. We report the characterization of the structures by a combination of different techniques. The x-ray-diffraction technique allows us to estimate the Al content x and to measure the period of the structure with good accuracy. Using the photographs given by high-resolution transmission electron microscopy on cleaved wedges, we investigate directly the key parameters of the structures, such as the regularity, the layer thickness, and the Al content x. The photoluminescence measurements carried out in detail from 4 K to room temperature show the excitonic character of the radiative recombination in these structures up to room temperature. The influence of x on the photoluminescence is investigated systematically. The data confirm the theoretical results calculated using finite barrier heights. The increase of transition energies with increasing x is due to the increase of confinement energies and exciton binding energies. A good agreement of the structure parameter values obtained by the above techniques is given.

The linear (r41) and quadratic (R11 and R12) electro‐optic coefficients of GaAs have been measured at the wavelengths 1.32 and 1.52 μm using single‐mode AlGaAs/GaAs strip‐loaded waveguides. The results are r41=−(1.54±0.08)×10−10 cm/V, R11=−(9.3±2.8)×10−17 cm2/V2 and R12=−(5.1±l.9)×10−17 cm2/V2 at 1.32 μm and r41=−(1.50±0.08)×10−10 cm/V, R11=−(3.2±2.3)×10−17 cm2/V2 and R12=−(5.1±2.6)×10−17 cm2/V2 at 1.52 μm. These results, together with those previously measured at different wavelengths, are compared with published theoretical models. The linear electro‐optic coefficient r41 is slightly dispersive near the band gap and roughly constant for longer wavelengths, in good agreement with the models. The quadratic electro‐optic coefficients drop rapidly with increasing wavelength, in good agreement with a model based on electroabsorption.

The mechanism of silicon diffusion in GaAs, Al0.3Ga0.7As, and the silicon diffusion-induced layer disordering of multiquantum wells have been studied by photoluminescence, secondary-ion-mass spectroscopy, and transmission electron microscopy across a corner of a wedge-shaped sample. The diffusion source was a grown in highly Si-doped layer. The main photoluminescence properties of point defects in GaAs and Al0.3Ga0.7As are reviewed to interpret the experimental data. The depth profile of the photoluminescence allows the spatial correlation between the luminescence spectra and the Si concentration profile obtained from secondary-ion-mass-spectroscopy measurements. On the basis of the photoluminescence results, the physical processes occurring during the Si diffusion are discussed. Frenkel defects (pairs of element-III vacancies and interstitials) are generated in the highly Si-doped region. The element-III interstitials rapidly diffuse towards the surface where they react with the element-III vacancies generated at the surface when annealing is performed in an external As pressure. This induces a supersaturation of element-III vacancies in the Si-doped region which drives the Si diffusion. Annealing in vacuum reduces the oversaturation of element-III vacancies and, hence, reduces the Si diffusion. A domination of the Si donor-element-III vacancy complex emission band was found in the spectra taken in the Si-diffused region. This gives evidence for the vacancy-assisted mechanism in the Si diffusion and in the impurity-induced disordering.

The authors have studied a binary (AlAs/GaAs) multilayer structure and a short-period ternary (AlGaAs/GaAs) superlattice with a central enlarged GaAs single quantum well grown by molecular beam epitaxy (MBE) and by means of X-ray diffraction (XRD) (involving synchrotron radiation) and photoluminescence (PL). Using careful simulations of the X-ray diffraction pattern, they have evaluated the width of the enlarged quantum well from the thickness oscillation features near the satellites. The well thicknesses obtained by XRD and PL are correlated and show agreement of the values concluded from these independent experimental methods. Based on numerical simulations, the features of the thickness oscillations are discussed in more detail with the intention of presenting possibilities appropriate for the analysis of artificially layered structures by means of XRD.

To study the effect of damage induced during the Zn diffusion on the properties of the material, p-n junctions, obtained by zinc diffusion, are investigated by electron beam induced current (EBIC) at different temperatures. At helium temperature, the EBIC decay on the p-side is flattened and non exponential. This effect is attributed to the defects induced by the Zn-diffusion that act as non-radiative centers. The room temperature EBIC signal has a symmetric exponential decay on both sides of the junction. The EBIC measurements for different temperatures and electron beam voltages indicate that the surface recombinations affect the carrier transport at room temperature hindering the non-exponential EBIC decay observed at helium temperature. The recombination dynamic is affected stronger by the as grown (001) surface than by the cleaved (110) surface.

Two types of InGaAs-GaAs-AlGaAs complex-coupled distributed feedback laser structures grown by molecular beam epitaxy are compared. The first structure uses interrupted quantum wells (QW's) grown over a grating. Its properties strongly depend on the interface cleaning resulting in nonreproducible threshold current densities. The second structure includes three uniform QW's, the gain coupling being induced by the vertical radiation of the second order grating. This last structure has reproducible, low continuous wave threshold current densities (jth=300 A/cm/sup 2/). The coupling strength and its origin are described for the two structures. Both structures have high mono-mode yield (>75%) and side-mode suppression ratios larger than 40 dB.

Using Hall effect and photoluminescence investigations the impurity incorporation was characterized on n-type MBE-grown AlxGa1-xAs:Si. Although the compensation ratio was small, silicon was also observed as both a donor and an acceptor in low doped material. Starting from the value in GaAs (EaSi(GaAs)=34.8 meV) the activation depth of the isolated silicon acceptor with respect to the valence band increases in the range 0

Annealing in excess arsenic vapor at 650-degrees-C introduces thermal conversion of n-type Si-doped GaAs samples (n = 1.3 X 10(18) cm-3) into p type. The observations are made by current-voltage and electron-beam induced current measurements. The donor concentration on the n side near the junction decreases after annealing. We present a comparison between the photoluminescence spectra of samples annealed under different conditions and an analysis of depth profile of the photoluminescence spectra. Our results underline the important role of gallium vacancies and gallium vacancy-silicon donor complex in the thermal conversion.

This paper describes a fabrication procedure for buried GaAlAs structures with lateral feature sizes in the nm range and with a high package density (periodicity Λ=135nm). GaAs substrates are finely structured by means of deep UV (λ=257nm) holographic lithography. We greatly improved this method by the application of a negative image reversal Novolak resist and an antireflective coating. Buried GaAs filaments are fabricated by growing GaAlAs/GaAs/GaAlAs quantum well (QW) structures on nonplanar substrates by molecular beam epitaxy (MBE). A crescent profile of the GaAs wires is obtained for [011] orientation of the grating lines. This is very attractive for the growth of quantum filaments (QF). Low temperature photoluminescence measurements reveal a high quality of QF grown by MBE over finely grooved substrates. The photoluminescence yielded by QF is comparable to that of QW grown on planar substrates.

We present the results of pseudopotential density-functional supercell calculations of the properties of neutral hydrogen in bulk GaAs. The equilibrium sites are determined, and the electronic properties for the equilibrium positions are studied. We find that the equilibrium site for unrelaxed GaAs:H is in the low-valence-charge-density region, whereas if the relaxation of the whole lattice is allowed, a shallow equilibrium minimum occurs at an antibonding site near an As ion. The diffusion path is in the high-valence-charge-density region around the As ions with a barrier as low as 0.1 eV. From our results, we suggest that H behaves as a deep acceptor in n-type GaAs and as a deep donor in p-type GaAs, and occupies different positions. Hence passivation of dopants occurs by neutralization.

This work aims at a systematic study of phase modulation in GaAs/AlGaAs double‐heterostructure waveguides with different doping profiles. Both theoretical (part I) and experimental (part II) aspects are investigated, leading to interesting new results. Phase modulation is the sum of a linear electro‐optic term, a quadratic electro‐optic term, and a free‐carrier term. The carrier term is shown to be the sum of a plasma term, an intervalence‐band term (for holes only), a band‐filling term, and a band‐shrinkage term, the latter being due to many‐body effects. A new analytic expression for the band‐filling term is derived which shows that the band‐filling effect does not depend on the carrier effective mass. We prove that the band‐shrinkage term is approximately half of the band‐filling term, but has opposite sign. The phase modulation is computed using an overlap integral between the optical intensity and the local refractive‐index difference. We also report an analytic expression for the modulation efficiency of a p‐i‐n junction double‐heterostructure modulator. This expression is very accurate and only requires knowledge of the depletion width and the guiding parameters.

Phase modulation in GaAs/AlxGa1−xAs double heterostructures with different doping profiles is systematically investigated. Very good agreement between the experimental measurements and the theory developed in Part I of this paper is reported. By measuring the phase modulation for both transverse electric and transverse magnetic modes along the [110] and [110] crystallographic directions, we are able to deduce accurate values for the linear electro‐optic coefficient. Values of r41=−1.68×10−10 cm/V at λ=1.15 μm and r41=−1.72×10−10 at λ=1.09 μm are obtained with an estimated accuracy of ±5%. An accurate estimation of the carrier effect permits us to deduce the quadratic electro‐optic coefficient for GaAs. The values are R11=−2.0×10−16 cm2/V2, R12=−1.7×10−16 cm2/V2 at λ=1.15 μm, and R11=−2.9×10−16 cm2/V2, R12=−2.4×10−16 cm2/V2 at λ=1.09 μm with an estimated uncertainty of ±25% for all values. Contrast measurement of Fabry–Perot fringes enables us to evaluate the modulator losses. A value of 4.8 cm−1 is repor...

Using the transfer matrix method the Kronig-Penney model is generalized to superlattices formed by whatever successions of layers. Imposing the boundary conditions, the miniband structure as well as the envelope wave functions are obtained. As examples, the “enlarged well in a superlattice” problem and the Fibonacci superlattices are discussed. The Lyapunov coefficients as a function of energy are calculated to determine the localization properties of the eigenstates in the entire superlattice spectrum. The single channel Landauer formula is used to get the conductance spectrum. Results are presented for random disordered superlattices. Mit der Methode der Transfermatrix werden das Kronig-Penney-Modell auf Supergitter mit beliebiger Schichtfolge verallgemeinert. Durch Einfuhrung der Grenzbedingungen werden sowohl die Minibandstruktur als auch die Einhullende der Wellenfunktionen erhalten. Als Beispiel werden das Problem des „ausgedehnten Grabens in einem Supergitter” sowie die Fibonacci-Supergitter diskutiert. Die Lyapunov-Koeffizienten werden als Funktionen der Energie berechnet, um die Lokalisierungseigenschaften der Eigenzustande im gesamten Supergitterspektrum zu bestimmen. Die Landauer-Einkanalformel wird benutzt, um das Leitwertspektrum zu erhalten. Es werden Ergebnisse fur statistisch fehlgeordnete Supergitter angegeben.

We have investigated the electro-optic properties of strained InGaAs/GaAs quantum wires of lateral width below 20 nm by means of electroluminescence and luminescence under electric bias. A novel room temperature electroluminescence is observed in MBE grown samples. The optical spectra reveal a strong red-shift and the suppression of the luminescence with increasing polarization either under reverse or direct bias. This anomalous Stark shift is due to the combination of the internal piezoelectric field and the external field.

We report a clear evidence of bistability in the current-voltage (I-V) characteristics of p - i - n heterostructures containing InGaAs V-shaped quantum wires. The observed phenomenon is explained in the framework of a single carrier transport model in which the quantum wires act like traps for the vertical current. The charge trapping phenomenon is indeed demonstrated by capacitance-voltage (C-V) and photocurrent experiments.

We present a comprehensive discussion of the excitonic properties of V-shaped GaAs and InGaAs quantum wires grown on patterned substrates. Systematic linear and non-linear spectroscopic studies have been performed in order to clarify the impact of lateral confinement on the exciton wave function, namely: enhanced exciton binding energy, localization in magnetic field, recombination from excited states and multiphoton absorption. The careful evaluation of the electron confinement energies, based on the actual quantum wire profile obtained by TEM micrographs, including the internal piezoelectric field induced by off-diagnoal terms of strain tensor, reproduces quite well the measured one-dimensional states. Finally, application of quantum wires in a p-i-n wave guide for bistable operation is demonstrated.

Fabrication and characterization of a current-injected InGaAs-GaAs quantum-wire gain-coupled distributed feedback (DFB) laser operating at 77 K at a wavelength of 923 nm are presented. Threshold current densities in broad area lasers were measured to be as low as 160 A/cm/sup 2/. The side-mode suppression ratio at twice threshold is 35 dB. A 4-/spl mu/m rib waveguide device has a threshold of 14 mA. The patterning process for the second-order DFB grating fabricated with deep UV holography and wet-chemical etching is described.