Peak Energy Shift Research Articles

QUANTUM WELLS IN OPTOELECTRONICS: GaAs/GaAlAs graded index separate confinement single quantum well single-mode waveguide electroabsorption light modulator

A GaAs/GaAlAs graded-index separate confinement single quantum well heterostructure single-mode ridge waveguide electroabsorption modulator was fabricated and investigated. For the modulator with a quantum well width of 100 Å and device length of 700 μm, an on/off ratio of 29.7 dB and estimated absorption insertion loss of 3 dB were obtained for TE polarised light with wavelength 8650 Å, and for TM polarisation the on/off ratio was 28.5 dB. With a switching voltage of 1 V, an on/off ratio of 15 dB was achieved. Photocurrent spectra exhibited a red shift of 600 Å of the absorption edge when the voltage applied to the PIN diode was varied from 0.5 to −7 V. The corresponding shift of the room temperature exciton peak energy was 96 meV.

Photoluminescence of quantum well structures with modulated layers grown by an alternating source supply

The photoluminescence (PL) spectra from modulated quantum well structures were observed. The modulated quantum well structure comprised a 4 monolayer (ML) modulated layer and an 18 ML GaAs layer between AlAs barrier layers. The modulated layer was grown by incorporating As into a Ga and Al mixture on an AlAs surface. The main peak energy of the PL spectra at 77 K showed a growth temperature dependence; a remarkable red shfit of the main peak energy was observed for samples grown at low temperature. The red shift of the PL peak energy indicates an increase in the effective width of the GaAs well. A rearrangement model of Ga and Al atoms on the AlAs surface during growth with As incorporation into the Ga and Al mixture is proposed to explain the growth temperature dependence of the PL peak energy.

Phonon Raman scattering of NbBa2Cu3Oy and Nd1.6Ba1.4Cu3Oy.

Polarized Raman scattering from ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ and ${\mathrm{Nd}}_{1.6}$${\mathrm{Ba}}_{1.4}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ single crystals is reported. Single-phonon peaks have been observed in ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ at 136, 168, 316, 448, 508, and 580 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at room temperature where the 316- and 580-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peaks are strong in the (x,x) while the 448- and 508-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peaks are strong in the (z,z) configurations. The 316-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peak is found to separate into two peaks at 290 and 323 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at 4 K, which are assigned as in-phase and out-of-phase vibration of oxygen atoms in the Cu-O plane, respectively. The polarization dependence of the scattering peaks has been explained on the basis of the characteristics of the electronic transitions. The energy shift of peaks when Ba is substituted by Nd has also been discussed.

Mode of growth in LP-MOVPE deposition of GalnAs/lnP quantum wells

GalnAs/lnP multiple quantum wells of 10 periods grown by low pressure metal organic vapor phase epitaxy were studied using a careful analysis of their photoluminescence (PL) spectra and of supporting x-ray data. The results demonstrate extremely precise control of the well width. The width of well and barrier can be reproducibly adjusted by a fraction of a monolayer. This allows one to distinguish between 3-dimensional (3-D) and 2-dimensional (2-D) growth, which determines the lateral extent of the atomically smooth interfacial areas. By varying the growth time per well a discontinuous energy shift of the PL peaks is obtained for wells with widths from 1 to 8 monolayers. We show that this discontinuous energy shift corresponds to a change in well width by one monolayer. It is also observed when growth at the upper interface is carried on without interruption and a thin quaternary film is deposited at the interface. From these results the presence of atomically flat surfaces during the growth is deduced; these give a strong indication of a 2-D mode of growth for an optimized set of parameters.

Photoluminescence and heavy doping effects in InP

Photoluminescence (PL) studies on LPE-grown InP layers doped with selenium and having carrier concentrations from 1 × 1018 to 1 × 1020 cm−3 have been reported in this paper. Measurements at 300 and 77 K showed that the band to band recombination peak energy shifts to values as high as 1·7 eV with increasing doping, the increase being sharp beyond 4 × 1019 cm−3. These results have been explained as being the result of the Burstein shift and the band-gap shrinkage.

Mass and dose dependence of ion-implantation-induced intermixing of GaAs/GaAlAs quantum-well structures

The influence of ion mass and dose on the intermixing of GaAs/GaAlAs quantum-well structures using photoluminescence (PL) and secondary-ion-mass spectroscopy (SIMS) techniques has been studied. Ga, Zn, Ar, Mg, Ne, and He ions are implanted in a single-quantum-well (SQW) structure at different doses. After annealing, the amount of intermixing between Al and Ga is extracted from the PL peak energy shift of the near-band-gap emission of the SQW. The measured Al diffusion length values ΔAl for different ion species agree with a simple model which assumes that the implantation damage in conjunction with low T (T<600 °C) defect diffusion is responsible for the mixing. We observe a similar dose dependence for ΔAl for all the above ions. For high implantation doses we have studied the mixing by Ar ions after implantation and annealing with SIMS. The SIMS data indicate that at high doses collisional mixing is the dominant mechanism for the disordering. Drastic mixing effects are obtained in the above quantum-well structures after high-temperature annealing of samples implanted with electrically active impurities (S,Si).

InGaAs/AWAsSb Heterostructures Lattice-Matched to InP GRown by Molecular Beam Epitaxy

ABSTRACTWe have successfully grown InGaAs/AIAsSb quantum-well (QW) structures lattice-matched to InP by molecular beam epitaxy for the first time. We studied the band-edge discontinuity and the interface abruptness of these heterostructures. A cross-sectional lattice image of InGaAs/AlAsSb QWs taken along the [100] axis showed atomically smooth heterointerfaces. The photoluminescence (PL) peak energy of the 20-nm-thick InGaAs well (0.758 eV) was lower than that of InGaAs bulk (0.799 eV), indicating that the InGaAs/AlAsSb system has a staggered lineup. The conduction band-edge discontinuity, ΔEc, was evaluated to be 1.74 ± 0.04 eV, which was derived from parameter fitting to the 4.2 K PL peak energy shifts of QWs as a function of InGaAs well width between 2.1 nm and 20 nm. The corresponding valence band-edge discontinuity, ΔEv, was 0.07 ± 0.02 eV. We also fabricated a resonant tunneling barrier structure of InGaAs (4.4 nm)/AlAsSb (2.9 nm), and obtained a very high peak-to-valley current ratio of 15 at 300 K.

Electroreflectance of ordered Ga 0.5In 0.5P Alloys

Electroreflectance (ER) spectra of ordered Ga 0.5In 0.5P alloys grown on GaAs by organometallic vapor phase epitaxy (OMVPE), have been investigated in the region of the E 0 and E 1 band edges, together with their photoluminescence (PL) measurements and transmission electron diffraction (TED) observation. The ordered OMVPE-grown Ga 0.5In 0.5P alloys have shown an anomalous shift of the PL peak energy at the E 0 band edge, and exhibit CuPt-type ordering. Growth temperature, V/III ratio and substrate orientation effects on ER spectra have been studied. The results reveal anomalous ER structures which appear in ordered OMVPE-grown Ga 0.5In 0.5P alloys on (001) GaAs and are not observed in bulk and LPE-grown Ga 0.5In 0.5P alloys. In particular, the ER structures observed at 2.2 and 2.4 eV have been explained by ordering-induced pseudodirect interband transitions. Substrate orientation effects have shown that the anomalous ER spectra are observed only on (001) GaAs substrates and not on (111)B GaAs substrates. This result suggests that the origin of the ordering in OMVPE-grown Ga 0.5In 0.5P alloys is closely related to the surface atomic structure of the GaAs substrate.

X‐Ray Emission Spectroscopy of the Electronic States in Pb1−xHgxS Thin Films

AbstractX‐ray emission specta in metals and alloys have been studied extensively. However, work on semiconductor alloy thin films is rather scarce. Here the sulphur Kα emission in Pb1−xHgxS thin films prepared by electroless deposition method is investigated. Films in the thickness range 0.2 to 0.3 μm are grown by this method. X‐ray emission spectra of SKα band in Pb1−xHgxS reveal the presence of three‐band structure at about 2, 5 to 7, and 17 to 18 eV from the Fermi level EF. The asymmetric index (x) is found to be higher than that of the pure SKα band. Alloying the film with Hg increases the α in the beginning and then decreases and finally increases it for HgS. It is observed that the density of states (DOS) at EF decreases for alloy thin films. From the shift in the Kα peak energy the charge associated with the S ion in these films is calculated. Besides, the bonding parameter (λ) is calculated from the charge and it is observed that for PbS, the bonding is homopolar and decreases with the increase in Hg concentration reaching a minimum nearer to neutral bonding value and thereafter it increases showing the bonding in HgS to be homopolar again. The satellite peaks are explained on the basis of hybridization of s– and p–d orbitals.

Determination of X‐ray fluorescence sample geometry from compton backscatter energy

AbstractA method was developed to determine automatically sample positions and correct peak intensities for sample positional variations in x‐ray fluorescence (XRF) analysis. Small shifts in Compton backscatter peak energy are accurately measured in the spectrum and used to compute the mean scatter angle, from which the effective scatter position is determined. New equations were derived to express fluorescent and scatter positions within samples, and to correct peak intensities for geometry variations in a sample of arbitrary thickness, position and composition. The method was validated with an energy‐dispersive XRF system with secondary excitation. With thin samples, the method corrected intensity errors of up to 69% to within 2%, and with samples of intermediate thickness it corrected errors of up to 83% to within 1.7%. The method is important in quantitative fundamental parameter calculations, such as the CEMAS method, which otherwise define the sample to lie in a pre‐determined plane.

Intermixing of InGaAs/InP multiple quantum well structures by Ga implantation

The effect of Ga implantation and thermal annealing on InGaAs/InP multiple quantum well structures is investigated by photoluminescence (PL) and sputtering Auger electron spectroscopy. It is found that the interdiffusion of both column III and column V atoms occurs at the interfaces between InP barrier and InGaAs well layers, but the degree of intermixing near the sample surface is small. The variations of PL peak energy shift with annealing and dose suggest that the PL peak shift is attributed to a combination of intermixing and stress.

A Study of Heteroepitaxy of InP on GaAs by Metalorganic Vapor‐Phase Epitaxy

The epitaxial layers of were grown on a substrate by atmospheric pressure metalorganic vapor‐phase epitaxy. By employing a two‐step growth procedure, an epitaxial layer with a specular surface and good crystalline quality could be obtained when a thin buffer layer (∼ 200Å) was deposited at low temperature (400°C) prior to the epitaxial growth. On the other hand, in the case of direct growth, a growth layer had a rough surface and poor crystalline quality, presumably due to island‐like growth and/or reaction of gas with in the early stage of epitaxy. Compressive stress and strain in the epitaxial layer was measured from the shift of the photoluminescence peak energy between the hetero‐ and homoepitaxial layers. The strain and stress was , respectively, which was explained by the difference of the thermal expansion coefficient between and .

Characterization of InP/GaAs epilayers grown on Si substrates by low-pressure organometallic vapor phase epitaxy

Heteroepitaxial growth of InP on Si with an intermediate GaAs buffer layer by low-pressure organometallic vapor phase epitaxy is reported. Excellent crystallinity of InP epilayers with specular surfaces can be reproducibly obtained. The carrier concentration profile shows that the carrier distribution in the InP layer is very uniform, while an apparent reduction in concentration occurs at the InP/GaAs interface. The 77 K photoluminescence (PL) of the InP layer exhibits a strong near-band-edge emission. No evident shift in PL peak energy for the InP/GaAs/Si sample compared with that for the InP homoepitaxial sample was first observed in this study. These results are superior to those reported previously for the InP/Si heteroepitaxy.

Growth and characterization of InP/GaAs epilayers on Si substrates by low-pressure metalorganic vapor phase epitaxy

Heteroepitaxial growth of InP on Si with an intermediate GaAs buffer layer by low-pressure metalorganic vapor phase epitaxy is reported. Single-crystal InP epilayers with specular surfaces can be reproducibly obtained. The uniform composition of this heterostructure was identified by the Auger depth profile. The best room-temperature electron mobility of the undoped InP epilayer can reach 3250 cm2/V·s with a carrier concentration of 1×1015 cm−3. It was found that the InP electron mobility is critically dependent on the growth temperature. The 77 K photoluminescence (PL) of the InP layer exhibits a strong near-band-edge emission. No evident shift in PL peak energy for the InP/GaAs/Si sample compared with that for the InP homoepitaxial sample was first observed in this study. An evident effect of the GaAs buffer-layer thickness on the InP optical quality is also demonstrated.

Improvements in resonance frequency and T0 value by 1.5 μm InGaAs MQW lasers grown by MOVPE

High quality InGaAs/InP quantum well structures and 1.5 μm MQW lasers, grown by low pressure MOVPE are reported. PL linewidth, PL peak energy shift, X-ray satellite peaks and transmission spectroscopy have demonstrated that the InGaAs/InP quantum wells were of high quality. The first improvements in T0 and resonance frequency in 1.5 μm MQW lasers are reported. Superior performances due to a quantum effect are: (1) high T0 value, 105 K (15–45°C), (2) large TE/TM mode gain difference, 45 cm−1 and (3) high resonance frequency, 4 GHz/mW12.

Crystallinity and interdiffusion in InP/InGaAs quantum wells grown by Hydride VPE

This paper reports the results of a study on interfacial quality and thermal interdiffusion for InP/InGaAs Quantum Wells (QW) grown by hydride VPE. By controlling well layer as thin as 25 Å, it was estimated that island and valley, whose height was one monolayer and whose lateral size was one third of exciton radius, existed at the interface. For the first time, interdiffusion coefficients for InP/InGaAs QW were obtained from 77K PL peak energy shift. Typical values were 2.5×10 −19 cm 2/sec and 1.5×10 −18 cm 2/sec for the annealing temperature of 700°C and 750°C, respectively. These values are over 10 2 times larger than that in AlGaAs/GaAs QW, and less 10 −2 times smaller than that in InAlAs/InGaAs QW.

Enhancement of quantum confined Stark effect in a graded gap quantum well

A graded gap quantum well structure, where the band gap is linearly changing along the growth direction, is proposed for the enhancement of quantum confined Stark effect. Theoretical calculations show that the ground-state exciton peak energy shifts by a larger amount than in a usual square-shaped quantum well under an applied electric field. The wave function modifications in this quantum well result in a smaller decrease of the exciton oscillator strength, according to the electric field applied. These effects reveal the possibility of achieving high-performance optical modulators or other devices which utilize the quantum confined Stark effect.

Energy calibration and peak shifts of Ni3Fe Auger spectra

A method of energy calibration of Auger spectra taken with a cylindrical-mirror-type energy analyser (c.m.a.) is proposed and applied to the spectra of Ni and Ni3Fe single-crystal surfaces. Energy shifts of Auger peaks caused by a change in the distance between the c.m.a. and the specimen have been calibrated by performing a regression calculation on the observed energy values of the Auger peaks. Auger spectra of the Ni3Fe single crystal recorded in the derivative mode [d N(E)/d E] exhibit peak shifts of the Fe LMM Auger lines to the high-energy side. This is due to the changes in distribution of the Fe 2p electron population which are produced by a lattice situation, such as a host–guest lattice of host Ni with 25% guest Fe.

ZnSe-ZnS strained-layer superlattice grown by low pressure metalorganic vapor phase epitaxy using methylalkyls

Good quality ZnSe-ZnS strained-layer superlattice (SLS) has been successfully fabricated for the first time by low pressure metalorganic vapor phase epitaxy (MOVPE) using methylalkyls (dimethylzinc, dimethylselenide, and dimethylsulfide). The satellite peak observed by x-ray diffraction measurements and the periodic behavior of the atomic profiles by secondary ion mass spectrometry measurements confirm the formation of the SLS structure. From the photoluminescence measurements, the quantum size effect has been evidenced by the relationship between the ZnSe well-layer thickness and the peak energy shift of the light emission. Our results show that low pressure MOVPE using VI group alkyls can be quite useful for the growth of ZnSe-ZnS SLS.

Field-induced exchange effects in (Cd,Mn)Te and (Cd,Mn)Se from photoluminescence measurements.

Photoluminescence measurements are made on the semimagnetic semiconductors ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te and ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se for 0<x\ensuremath{\le}0.15. Large energy shifts (\ensuremath{\sim}50 meV) of the exciton recombination peaks and large optical polarizations (\ensuremath{\sim}100%) are produced by applying a magnetic field. This study examines changes in luminescence using magnetic fields up to B=15 T and at temperatures between T=1.5 and 60 K. When viewed along the direction of the field (Faraday geometry), the luminescence due to both exciton recombination and impurity-related transitions becomes circularly polarized. At T=2 K the polarization shows saturation at only 0.5 T.This low saturation field results from the large internal exchange field which produces large spin Zeeman splitting of the bands. We found that the polarization gives a quantitative measure of the exchange effects even when the luminescence features are broader than the splittings. In the Voigt geometry (luminescence observed perpendicular to the magnetic field), the linear polarization gives information on the orbital part of the wave functions of the recombining carriers. Differences in the polarization of the two exciton-related peaks in the (Cd,Mn)Te spectra indicate that one peak arises from an acceptor-bound exciton complex and the second to a simple electron-hole exciton. The latter is attributed to a trapped exciton. With increasing magnetic field, both the (Cd,Mn)Te and (Cd,Mn)Se spectra show splittings of the bound exciton related peaks.At low fields the low-energy feature dominates while at high fields the higher-energy feature is dominant. This is attributed to a field-induced instability of the binding of the exciton to the impurity, resulting from the exchange interaction and Pauli exclusion. At high magnetic fields and low temperature the energy of the exciton peak shows a step in the field-tuning curve. This step reflects a transition of the antiferromagnetically coupled nearest-neighbor manganese ion pair. A value of J/k=-8.4 K is determined for the exchange constant. Finally, the luminescence spectra indicate that samples grown by liquid-phase epitaxy and the traveling-solvent method have much higher purity than Bridgman-grown materials. The manganese concentrations in (Cd,Mn)Te are determined from the energies of the exciton luminescence peaks.