Interdiffusion effect on GaAsSbN/GaAs quantum well structure studied by 10-band k•p model

The effect of annealing on the photoluminescence (PL) in GaAsSbN/GaAs quantum well (QW) grown by solid-source molecular-beam epitaxy (SS-MBE) has been investigated. Low-temperature (4 K) PL peaks shift to higher energy sides with the increase of annealing temperature. An As-Sb atomic interdiffusion at the heterointerface is proposed to model this effect. The compositional profile of the QW after interdiffusion is modeled by an error function distribution and calculated with the 10-band k•p method. When the diffusion length equals to 1.4 nm, a corresponding transition energy blueshift of 36 meV is derived. This agrees with the experimental result under the optimum condition (750 °C at 5 min).     

(In)GaSb/AlGaSb quantum wells grown on Si substrates

We have successfully grown GaSb and InGaSb quantum wells (QW) on a Si(001) substrate, and evaluated their optical properties using photoluminescence (PL). The PL emissions from the QWs at room temperature were observed at around 1.55 μm, which is suitable for fiber optic communications systems. The measured ground state energy of each QW matched well with the theoretical value calculated by solving the Schrödinger equation for a finite potential QW. The temperature dependence of the PL intensity showed large activation energy (∼ 77.6 meV) from QW. The results indicated that the fabricated QW structure had a high crystalline quality, and the GaSb QW on Si for optical devices operating at temperatures higher than room temperature will be expected.     

Tuning optical properties of high In content InGaAs/GaAs capped InAs quantum dots by post growth rapid thermal annealing

The effect of rapid thermal annealing on InAs quantum dots (QDs) capped with In_0.4Ga_0.6As/GaAs layer has been investigated by photoluminescence (PL). An unusual red shift of the PL emission peak has been observed for an annealing temperature (T_a) of 650 °C together with a pronounced improvement of the PL from the quantum well like heterocapping layer (QW). This behavior is attributed to the strain induced phase separation of the hetero-capping alloy. However, for T_a = 750 °C, a blue shift of the QDs PL peak has been observed with respect to that of the as-grown sample. For this annealing temperature the PL intensity of the QW exceeds that of the QDs indicating a relatively prominent In/Ga interdiffusion. When annealed at 850 °C, only the PL arising from the QW can be detected in addition to a broadened low energy side band indicating the dissolution of the QDs at that temperature.     

Effect of post-growth rapid thermal annealing on bilayer InAs/GaAs quantum dot heterostructure grown with very thin spacer thickness

We have investigated the effect of post-growth rapid thermal annealing on self-assembled InAs/GaAs bilayer quantum dot samples having very thin barrier thickness (7.5-8.5 nm). In/Ga interdiffusion in the samples due to annealing is presumed to be controlled by the vertical strain coupling from the seed dots in bilayer heterostructure. Strain coupling from embedded seed QD layer maintains a strain relaxed state in active top islands of the bilayer quantum dot sample grown with comparatively thick spacer layer (8.5 nm). This results in minimum In/Ga interdiffusion. However controlled interdiffusion across the interface between dots and GaAs barrier, noticeably enhances the emission efficiency in such bilayer quantum dot heterostructure on annealing up to 700 °C.     

Unusual changes observed in the photoluminescence of annealed InxGa1 − xN/GaN quantum wells explained

In_xGa_1 − xN/GaN heterostructures and quantum wells (QWs) are particularly important in the application of III-V nitride materials for light emitting diodes and laser diodes. The photoluminescence (PL) emissions from In_xGa_1 − xN/GaN QW structures have been reported, where, for successive annealing operations, the PL peak suffers a primary red shift, followed by a blue shift. The observed phenomenon remains unexplained because of its complexity. This paper is intended towards a proper explanation of the observed experimental results through suitable quantum mechanical models and computations, whether the band gap of InN is 1.95 eV or 0.7 eV.     

An approach to suppress the blue-shift of photoluminescence peaks in coupled multilayer InAs/GaAs quantum dots by high temperature post-growth annealing

Effect of post-growth annealing on 10 layer stacked InAs/GaAs quantum dots (QDs) with InAlGaAs/GaAs combination capping layer grown by molecular beam epitaxy has been investigated. The QD heterostructure shows a low temperature (8 K) photoluminescence (PL) emission peak at 1267 nm. No frequency shift in the peak emission wavelength is seen even for annealing up to 700 °C which is desirable for laser devices requiring strict tolerances on operating wavelength. This is attributed to the simultaneous effect of the strain field, propagating from the seed layer to the active layer of the multilayer QD (MQD) and the indium atom gradient in the capping layer due to the presence of a quaternary InAlGaAs layer. Higher activation energy (of the order of ∼250 meV) even at 650 °C annealing temperature also signifies the stronger carrier confinement potential of the QDs. All these results demonstrate higher thermal stability of the emission peak of the devices using this QD structure.     

Photoreflectance study of strained GaAsN/GaAs T-junction quantum wires grown by metal-organic vapor phase epitaxy

Strained GaAsN T-junction quantum wires (T-QWRs) with different N contents grown on GaAs by two steps metal-organic vapor phase epitaxy in [001] and [110] directions, namely QW1 and QW2 respectively, have been investigated by photoreflectance (PR) spectroscopy. Two GaAsN T-QWRs with different N contents were formed by T-intersection of (i) a 6.4-nm-thick GaAs0.89N0.011 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2 and (ii) a 5.0-nm-thick GaAs0.985N0.015 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2. An evidence of a one-dimensional structure at T-intersection of the two QWs on the (001) and (110) surfaces was established by PR resonances associated with extended states in all the QW and T-QWR samples. It is found that larger lateral confinement energy than 100 meV in both of [001] and [110] directions were achieved for GaAsN T-QWRs. With increasing temperature, the transition energy of GaAsN T-QWRs decreases with a faster shrinking rate compared to that of bulk GaAs. Optical quality of GaAsN T-QWRs is found to be affected by the N-induced band edge fluctuation, which is the unique characteristic of dilute III-V-nitrides.     

Optical evidence of a quantum well channel in low temperature molecular beam epitaxy grown Ga(AsBi)/GaAs nanostructure

A Ga(AsBi) quantum well (QW) with Bi content reaching 6% and well width of 11 nm embedded in GaAs is grown by molecular beam epitaxy at low temperature and studied by means of high-resolution x-ray diffraction, photoluminescence (PL), and time-resolved PL. It is shown that for this growth regime, the QW is coherently strained to the substrate with a low dislocation density. The low temperature PL demonstrates a comparatively narrow excitonic linewidth of ～ 40 meV. For high excitation density distinct QW excited states evolve in the emission spectra. The origins of peculiar PL dependences on temperature and excitation density are interpreted in terms of intra-well optical transitions.     

Time-resolved photoluminescence of type-II Ga(As)Sb/GaAs quantum dots embedded in an InGaAs quantum well

Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4?K) time-resolved PL measurements show a decay time of [Formula: see text]?ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text]?ns).     

Photoluminescence study and parameter evaluation in InAs quantum dot-in-a-well structures

The photoluminescence (PL), its temperature and power dependences have been studied in InAs quantum dots (QDs) embedded in the symmetric In_0.15Ga_0.85As/GaAs quantum well (QW) with QDs grown at different temperatures (470-535 °C). The ground state (GS) PL peaks shift with increasing QD growth temperatures: the red shift is observed when temperature increased from 480 to 510 °C and the blue shift is typical when the temperature raised from 510 to 535 °C. The fitting procedure (on the base of Varshni relation) has been applied to the analysis of GS PL peak positions versus temperatures. Obtained fitting parameters are compared with corresponding data for the temperature variation of energy band gap in the bulk InAs crystal and in the In_0.21Ga_0.79As alloy. The comparison has revealed that the structures with QDs grown at 490-510 °C have the same fitting parameters as the bulk InAs crystal. However in structures with QDs grown at the temperatures 470, 525 and 535 °C the fitting parameters testify that Ga/In inter-diffusion between QDs and a QW has been realized. It is shown that the Ga/In inter-diffusion process is accompanied by the appearance of nonradiative recombination defects.     

Enhanced control over selective-area intermixing of In0.15Ga0.85As/GaAs quantum dots through post-growth exposure to radio-frequency plasma

Post-growth treatment with a low pressure, CF₄-plasma is demonstrated to reliably inhibit the interdiffusion of In and Ga atoms in In_0.15Ga_0.85As/GaAs self-assembled quantum dot wafer structures subjected to rapid thermal annealing temperatures between 700 °C and 800 °C for a duration of 20 s. Comparative studies of the effects of rapid thermal annealing were made on plasma treated samples and samples that were capped with either 200 nm of plasma enhanced chemical vapor deposited SiO₂ or 220 nm of thermally deposited TiO₂ prior to plasma exposure, as well as to uncapped, untreated control samples. Room-temperature photoluminescence spectra were acquired using a Ti-Sapphire laser operating at 742 nm as the excitation source. A bandgap differential of 84 meV (94 nm) was measured across a wafer sample annealed at 775 °C, when contrasting sections that were uncapped and treated with the CF₄-plasma versus sections that were annealed without any treatment to the surface. This was comparable to a sample that was capped with the TiO₂ film, which produced a 73.5 meV (82 nm) variance from the raw, annealed-only sample.     

Optical and Magnetic Properties of Ten-Period InGaMnAs/GaAs Quantum Wells

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T _C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T _C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.     

Growth of GaInAs/AlInAs heterostructure nanowires for long-wavelength photon emission

We investigated the growth of GaInAs/AlInAs heterostructure nanowires on InP(111)B and Si(111) substrates in a metalorganic vapor phase epitaxy reactor. Au colloids were used to deposit Au catalysts 20 and 40 nm in diameter on the substrate surfaces. We obtained vertical GaInAs and AlInAs nanowires on InP(111)B surfaces. The GaInAs nanowires capped with GaAs/AlInAs layers show room-temperature photoluminescence. The peak exhibits a blue-shift when the Ga content in the core GaInAs nanowire is increased. For the GaInAs/AlInAs heterostructure growth, it is possible to change the Ga content sharply but Al also exists in the GaInAs layer regions. We also found that the ratios of Ga and Al contents to In content tend to increase and the axial growth rate to decrease along the nanowire toward the top. We were also able to make vertical GaInAs nanowires on Si(111) surfaces after a short growth of GaP and InP.     

Fabrication of surface metal nanoparticles and their induced surface plasmon coupling with subsurface InGaN/GaN quantum wells

Based on the fabrication of Ag nanoparticles (NPs) with controlled geometry and surface density on an InGaN/GaN quantum well (QW) epitaxial structure, which contains indium-rich nano-clusters for producing localized states and free-carrier (delocalized) states in the QWs, and the characterization of their localized surface plasmon (LSP) coupling behavior with the carriers in the QWs, the interplay behavior of LSP coupling with carrier delocalization in the QWs is demonstrated. By using the polystyrene nanosphere lithography technique with an appropriate nanosphere size and adjusting the post-fabrication thermal annealing condition, the induced LSP resonance wavelength of the fabricated Ag NPs on the QW sample can match the QW emission wavelength for generating the coherent coupling between the carriers in the QWs and the induced LSP. The coupling leads to the enhancement of radiative recombination rate in the QWs and results in increased photoluminescence (PL) intensity, red-shifted PL spectrum, reduced PL decay time, and enhanced internal quantum efficiency. It is found that the observed effects are mainly due to the LSP coupling with the delocalized carriers in the QWs.     

Selective modification of the band gaps of GaInNas/GaAs structures by quantum well intermixing techniques

We report the unambiguous demonstration of controlled quantum well intermixing (QWI) in the technologically important GaInNAs/GaAs 1.3 μm material system. QWI is a key technique to selectively modify the band gap of quantum wells, which has found broad application in semiconductor lasers and photonic integrated circuits (PICs). Extending such technology to GaInNAs/GaAs structures is highly desirable due to the technologically advantageous properties of this material system. Here, we investigate well-characterized GaInNAs quantum well material which has been annealed “to saturation” before QWI processing to allow unambiguous interpretation of results. After RTA at 700 °C for ∼180 s, controlled shifts in band-gap at room temperature of up to 200 nm have been observed in sputtered SiO₂-capped samples, whilst uncapped and PECVD SiO₂-capped samples demonstrated negligible shift. This selective modification of the band gap has been confirmed by detailed photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy. Analysis of composition profile by SIMS revealed that the QWI is due to the interdiffusion of In–Ga between the quantum wells and the barriers enhanced by the point defects generated during the sputtering process. Investigation of a series of samples of differing N concentrations will be presented, which provides extra information about the intrinsic properties of GaInNAs.     

InAs0.45P0.55/InP strained multiple quantum wells intermixed by inductively coupled plasma etching

The intermixing effect on InAs_0.45P_0.55/InP strained multiple quantum wells (SMQWs) by inductively coupled plasma (ICP) etching and rapid thermal annealing (RTA) is investigated. Experiments show that the process of ICP etching followed RTA induces the blue shift of low temperature photoluminescence (PL) peaks of QWs. With increasing etching depth, the PL intensities are firstly enhanced and then diminished. This phenomenon is attributed to the variation of surface roughness and microstructure transformation inside the QW structure during ICP processing.     

Influence of buffer surface preparation on the quality of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs quantum wells studied by optical orientation experiments

Quantum well (QW) structures of Al _x Ga_1-x As/GaAs with x = 0.3 were characterized by photoluminescence spectroscopy (PL) with circularly polarized excitation at a temperature of 1.6 K. The samples contained three QWs with thickness of 7, 5, and 3 nm grown by molecular beam epitaxy (MBE) on a 500 nm thick buffer layer. Four samples with identical geometry but different surface treatments (in-situ etching the GaAs buffer with Cl₂ at different temperatures, and air-exposed buffer, respectively) were compared. The degree of circular polarization of the PL and its decrease in a magnetic field applied perpendicularly to the direction of propagation of light (Hanle effect) allows the determination of the interband lifetime τ and the spin lifetime τ _s of the electrons. These lifetimes were different in the different QWs and strongly depend on the growth procedure.     

Mechanism of low energy S+ ion bombarded p-GaAs (100)

X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) have been used to characterize the chemical structure and site location of sulfur atom on p-GaAs (100) treated by bombardment of low energy S⁺ ions over the range from 10 to 100 eV. S⁺ ion bombardment resulted in the formation of Ga–S and As–S species on GaAs surface. It was found that the S⁺ ions with energy above 50 eV were more effective in formation of Ga–S species, which assisted the GaAs (100) surface in reconstruction into an ordered (1 × 1) structure upon annealing. After taking into account physical damage due to the process of ion bombardment, we found that 50 eV was the optimal ion energy to form Ga–S species in the sulfur passivation of GaAs (100). The subsequent annealing process removed both donor and acceptor states that were introduced during the ion bombardment of GaAs, and resulted in a sharp (1 × 1) LEED pattern.     

Giant Zeeman Splitting of Excitons in a III–V Nonmagnetic Quantum Well Electronically Coupled With a II–VI Semimagnetic Quantum Well

We report on design, fabrication by molecular beam epitaxy, and photoluminescence (PL) studies of GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum wells (QWs), where resonant electronic coupling occurs through a heterovalent interface. The resonant conditions achieved in the properly designed sample facilitate penetration of the electron wave function from the nonmagnetic GaAs QW into the diluted magnetic semiconductor ZnCdMnSe QW. It results in the sign reversal and drastic increase of a GaAs QW excitonic g factor. The exciton spin splitting observed in the magneto-PL spectra is in general agreement with the calculation performed within the envelope function approximation, taking into account both the inter-well electron coupling and Brillouin-like paramagnetic behavior of the Mn²⁺ ions.     

NEXAFS and XPS study of GaN formation on ion-bombarded GaAs surfaces

Interaction of low-energy nitrogen ions (0.3-2 keV N₂⁺) with GaAs (100) surfaces has been studied by X-ray photoemission spectroscopy (XPS) around N 1s and Ga 3d core-levels and near-edge X-ray absorption fine structure (NEXAFS) around the N K-edge, using synchrotron radiation. At the lowest bombardment energy, nitrogen forms bonds with both Ga and As, while Ga-N bonds form preferentially at higher energies. Thermal annealing at temperatures above 350 °C promotes formation of GaN on the surface, but it is insufficient to remove disorder introduced by ion implantation. We have identified nitrogen interstitials and anti-sites in NEXAFS spectra, while interstitial molecular nitrogen provides a clear signature in both XPS and NEXAFS. The close similarity between NEXAFS spectra from thin GaN films and ion-bombarded GaAs samples supports our proposition about formation of thin GaN films on ion-bombarded GaAs.