In-Ga Interdiffusion Research Articles

The coupling between two heterogeneous InAs quantum dot families and its effect into optical properties

Abstract:In this study, we present the coupling between InAs submonolayer (SML) and stranski krastanov (SK) quantum dots (QDs). Interaction between these two different dot families has been manipulated by changing the capping layer thickness. Significant shift in photoluminescence (PL) peak is observed due to the coupling effect. The dynamics of the carriers in this mixed dot matrix has also been modified, which is evident from the increasing activation energy with increasing thickness of the capping layer. Moreover, an ex situ annealing study at different temperatures has been done to check the thermal stability of the as-grown samples. Annealing at lower temperatures, improves the crystal quality a bit, but higher annealing temperatures accelerate the In-Ga interdiffusion and form smaller dots, which is visible from a blue shift in the PL peak of annealed samples. Also, this thermal process improves the dot size distribution.

Photoluminescence probing of interface evolution with annealing in InGa(N)As/GaAs single quantum wells

The effects of thermal annealing on the interfaces of InGa(N)As/GaAs single quantum wells (SQWs) are investigated by excitation-, temperature-, and magnetic field-dependent photoluminescence (PL). The annealing at 750 °C results in more significant blueshift and narrowing to the PL peak than that at 600 °C. Each of the PL spectra can be reproduced with two PL components: (i) the low-energy component (LE) keeps energetically unchanged, while the high-energy component (HE) moves up with excitation and shows at higher energy for the In0.375Ga0.625As/GaAs but crosses over with the LE at a medium excitation power for the In0.375Ga0.625N0.012As0.988/GaAs SQWs. The HE is broader than the corresponding LE, the annealing at 750 °C narrows the LE and HE and shrinks their energetic separation; (ii) the PL components are excitonic, and the InGaNAs shows slightly enhanced excitonic effects relative to the InGaAs SQW; (iii) no typical S-shape evolution of PL energy with temperature is detectable, and similar blueshift and narrowing are identified for the same annealing. The phenomena are mainly from the interfacial processes. Annealing improves the intralayer quality, enhances the interfacial In-Ga interdiffusion, and reduces the interfacial fluctuation. The interfacial interdiffusion does not change obviously by the small N content and hence similar PL-component narrowing and blueshift are observed for the SQWs after a nominally identical annealing. Comparison with previous studies is made and the PL measurements under different conditions are shown to be effective for probing the interfacial evolution in QWs.

Annealing effects on InGaAsN∕GaAs quantum wells analyzed using thermally detected optical absorption and ten band k−p calculations

The effects of thermal annealing for In0.25Ga0.75As1−yNy∕GaAs multiquantum wells (MQWs) have been investigated through thermally detected optical absorption. The QW transition energies have been calculated by using a ten-band k−p model including the band anticrossing model for the description of the InGaAsN band gap variation. The modification of the In concentration profile due to In-Ga interdiffusion during thermal annealing is taken into account through the Fick law. A good agreement is obtained between calculated and experimental energies of optical transitions. Our results show that the In-Ga interdiffusion phenomenon observed in a nitrogen free sample is moderately enhanced by the introduction of nitrogen. The blueshift of optical transitions induced by the annealing process is the result of both In-Ga interdiffusion and rearrangement of local nitrogen environment.

Diffusion mechanisms of indium and nitrogen during the annealing of InGaAs quantum wells with GaNAs barriers and GaAs spacer layers

In this article, we discuss two indium diffusion mechanisms that are present during the rapid thermal annealing of InxGa1−xAs quantum wells (x=0.18, 0.22, and 0.26) with GaNyAs1−y barriers (y=0.6 or 1.2%). Samples were grown with and without a GaAs spacer layer in between the quantum well and barrier. The dominant mechanism is dependent on the amount of thermal energy applied during the annealing process. At low annealing times and temperatures, we have observed that In-Ga intra-diffusion entirely within the quantum well is dominant. For the higher times and temperatures, In-Ga inter-diffusion between the quantum well and barrier becomes dominant. These observations were confirmed by high-resolution x-ray diffraction and the peak emission wavelengths were measured by room-temperature photoluminescence. We have also observed that nitrogen had diffused from the GaNAs barriers into the InGaAs quantum wells in all of our annealed samples. In addition, the commonly observed indium-content dependent diffusion in GaInNAs-based systems was not observed with InGaAs∕GaNAs-based structures.

Diffusion of Ga and In in Sequentially Prepared Cu(In, Ga)S2 Thin Films for Photovoltaic Applications

AbstractThis contribution investigates the diffusion of In and Ga in Cu(In1-xGax)S2 thin film absorbers for photovoltaic applications. Sequentially prepared Cu-rich CuGaS2/CuInS2thin film diffusion couples have been annealed at temperatures in the range of 500°C to 600°C. Annealed samples have been examined by XRD and SNMS depth profiling. It was found that despite significant interdiffusion of Ga and In the bilayer retains its two phase structure of two layers of almost homogeneous composition, where the composition of these layers depends on the annealing temperature. Furthermore the interdiffusion process is less effective if the binary copper-sulfide phase is removed before annealing. On the basis of a tentative two dimensional diffusion model, which includes rapid diffusion along path ways of high diffusivity, the Ga-depth distribution could be modeled by numerical fits of calculated XRD-spectra to the experimental data. CuS is proposed as a possible pathway for rapide In-Ga interdiffusion.

Effect of Thermal Annealing on the Photoluminescence Properties of a GaInNAs/GaAs Single Quantum Well

ABSTRACTWe report on the effect of thermal annealing on the photoluminescence properties of a Ga0.65In0.35N0.02As0.98/GaAs single quantum well. Thermal annealing is shown to decrease the strong nitrogen-induced localization effects observed at low temperatures and to reduce the full width at half maximum of the emission peak. It also induces a strong blue shift of the emission peak energy, which is thought not to arise from an In-Ga interdiffusion alone, as it is much larger than in a nitrogen-free reference single quantum well.

Process parameter dependence of impurity-free interdiffusion in GaAs/AlxGa1−xAs and InxGa1−yAs/GaAs multiple quantum wells

The dependence of the impurity-free interdiffusion process on the properties of the dielectric cap layer has been studied, for both unstrained GaAs/AlxGa1−xAs and pseudomorphic Iny Ga1−yAs/GaAs MQW structures grown by molecular beam epitaxy. The influence of the cap layer thickness, composition, and deposition technique on the degree of interdiffusion were all systematically investigated. Electron-beam evaporated SiO2 films of varying thickness, chemical-vapor-deposited SiOxNy films of varying composition, and spin-on SiO2 films were used as cap layers during rapid thermal annealing (850-950°C). Photoluminescence at 10K has been employed to determine the interdiffusioninduced bandgap shifts and to calculate the corresponding Al-Ga and In-Ga interdiffusion coefficients. The latter were found to increase with the cap layer thickness (e-beam SiO2) up to a limit determined by saturation of the outdiffused Ga concentration in the SiO2 caps. A maximum concentration of [Ga] = 4–7 ×1019 cm−3 in the SiO2 caps was determined using secondary ion mass spectroscopy profiling. Larger band-edge shifts are also obtained when the oxygen content of SiOxNy cap layers is increased, although the differences are not sufficiently large for a laterally selective interdiffusion process based on variations in cap layer composition alone. Much larger differences are obtained by using different deposition techniques for the cap layers, indicating that the porosity of the cap layer is a much more important parameter than the film composition for the realization of a laterally selective interdiffusion process. For the calculated In0.2Ga0.8As/GaAs interdiffusion coefficients, activation energies EA and prefactors Do were estimated to ranging from 3.04 to 4.74 eV and 5 × Kh−3 to 2 × 105 cm2/s, respectively, dependent on the cap layer deposition technique and the depth of the MQW from the sample surface.

An Optical Study of Interdiffusion in Strained InP-Based Heterostructures

The interdiffusion behavior of In1-x Gax As1-y Py /In1-x ′ Gax ′ As1-y ′ Py ′ multiple quantum well heterostructures with varied built-in strain and layer thicknesses, has been investigated by monitoring their photoluminescence (PL) properties. All samples annealed at 850° C, have consistently exhibited a blueshift of the heavy hole exciton line as a result of atoms interdiffusion across the heterointerfaces. A quantitative analysis of their PL spectra permitted to deduce the following important characteristics of the interdiffusion process: (i) From the data on a nearly strain-compensated structure with constant P/As ratio and In-rich wells, studied here for the first time, we show that the blueshift of the excitonic line is consequent of group III atoms interdiffusion alone, like in GaAs/GaAlAs system, and the In-Ga interdiffusion can be described with a diffusion coefficient D In-Ga≈4.72×10-16 cm2/s; (ii) In the case of lattice matched and compressively-strained structures, a simultaneous interdiffusion on group III and V sublattices has been assumed to yield an effective interdiffusion coefficient ranging from 3.83 to 5.51×10-16 cm2/s.

Impurity-induced disorder in strained InGaAs/GaAs quantum wells by Zn diffusion and thermal annealing

The authors report the investigation of impurity-induced disordering (IID) in strained InxGa1-xAs/GaAs (x=0.21-0.24) single quantum well (QW) heterostructures using a two-stage Zn diffusion and thermal annealing process. The samples were grown by MOVPE, and different shallow Zn diffusion depths were allowed in the GaAs cap layer in order to vary the Zn concentration in the QW. Thermal annealing of the samples at 785 degrees C for 10 min under an AsH3/H2 atmosphere then created IID. Both partially disordered and completely disordered QW heterostructures were studied. The In-Ga interdiffusion was monitored by the photoluminescence PL spectroscopy of the ground state emission from the QW. The interdiffusion coefficients were determined by adjusting the data calculated by using the envelope function approximation with the shifts of the PL peak position after the annealing. The interdiffusion coefficient is found to be very strongly dependent on the Zn diffusion depth, and consequently on the Zn concentration in the QW layer. Finally, they propose a model that involves an interstitial migration process in order to explain the enhancement of In-Ga interdiffusion by Zn diffusion.

Disorder of a GaxIn1-xAsyP1-y-InP quantum well by Zn diffusion

Data are presented showing for the first time that Zn diffusion into a GaxIn1-xAsyP1-y-InP quantum well and superlattice (of 100 Å thickness) completely disorders the quantum well and superlattice layers. The photoluminescence wavelength of the quantum well and the superlattice increased after Zn diffusion, which can be attributed to the In-Ga interdiffusion at the heterointerfaces as a result of the interchange mechanism between the interstitials and substitutional zinc atoms.