Polarization-Dependent Ultrafast Carrier Dynamics in GaAs with Anisotropic Response

The transient dynamics of anisotropic properties of GaAs is systematically studied by polarization-dependent ultrafast time-resolved transient absorption. Our findings revealed that the anisotropy of reflectivity was enhanced in both pump-induced and probe-induced processes, suggesting an extraordinary resonance absorption of photon-phonon coupling (PPC) with intrinsic anisotropic characteristic in carrier relaxation, regardless of the concrete crystallinity and orientation of GaAs sample. The results, delivering in-depth cognition about the polarization-dependent ultrafast carrier dynamics, also proved the paramount importance of interaction between polarized laser and semiconductor.

On the Study of Dislocation Density in MBE GaSb-Based Structures

The results of the study on threading dislocation density (TDD) in homo- and heteroepitaxial GaSb-based structures (metamorphic layers, material grown by applying interfacial misfit array (IMF) and complex structures) deposited using molecular beam epitaxy are presented. Three measurement techniques were considered: high-resolution x-ray diffraction (HRXRD), etch pit density (EPD), and counting tapers on images obtained using atomic force microscopy (AFM). Additionally, high-resolution transmission electron microscopy (HRTEM) was used for selected samples. The density of dislocations determined using these methods varied, e.g., for IMF-GaSb/GaAs sample, were 6.5 × 108 cm−2, 2.2 × 106 cm−2, and 4.1 × 107 cm−2 obtained using the HRXRD, EPD, and AFM techniques, respectively. Thus, the value of TDD should be provided together with information about the measurement method. Nevertheless, the absolute value of TDD is not as essential as the credibility of the technique used for optimizing material growth. By testing material groups with known parameters, we established which techniques can be used for examining the dislocation density in GaSb-based structures.

Intersubband Absorption in Gallium Arsenide Implanted with Silicon Negative Ions

Gallium arsenide (GaAs) implanted with silicon forming intersubband of SiGaAs is a promising material for making novel electronic and optoelectronic devices. This paper is focused on finding optimum fluence condition for formation of intersubband of SiGaAs in GaAs sample after implantation with 50[Formula: see text]keV silicon negative ions with fluences varying between [Formula: see text] and [Formula: see text] ions cm[Formula: see text]. The GaAs samples were investigated using X-ray photoelectron spectroscopy (XPS), UV-Vis.-NIR spectroscopy and X-ray diffraction (XRD) techniques. The X-ray photoelectron spectra for unimplanted sample showed peaks at binding energy of 18.74[Formula: see text]eV and 40.74[Formula: see text]eV indicating Ga3d and As3d core level, whereas the corresponding core level peaks for implanted sample were observed at binding energy of 19.25[Formula: see text]eV and 41.32[Formula: see text]eV. The shift in Ga3d and As3d core levels towards higher binding energy side in the implanted sample with respect to unimplanted sample were indicative of change in chemical state environment of Ga–As bond. The relative atomic percentage concentration of elemental composition measured using casa XPS software showed change in As/Ga ratio from 0.89 for unimplanted sample to 1.13 for sample implanted with the fluence of [Formula: see text] ion cm[Formula: see text]. The UV-Vis-NIR spectra showed absorption band between 1.365[Formula: see text]eV and 1.375[Formula: see text]eV due to the formation of intersubband of SiGaAs for fluences greater than [Formula: see text] ion cm[Formula: see text]. The GaAs crystallite size calculated using Brus formula was found to vary between 162[Formula: see text]nm and 540[Formula: see text]nm, respectively. The XRD spectra showed the presence of Bragg’s peak at 53.98∘ indicating (311) silicon reflection. The silicon crystallite size determined from full width at half maxima (FWHM) of (311) XRD peak was found to vary between 110[Formula: see text]nm and 161[Formula: see text]nm, respectively.

Photoreflectance study of the GaAs buffer layer in InAs/GaAs quantum dots

GaAs buffer layer in InAs/GaAs quantum dots (QDs) was investigated by Photoreflectance (PR) technique at 300 K. PR spectra obtained were compared with commercial GaAs sample PR spectra, and they were analyzed by using the derivative Lorentzian functions as proposed by Aspnes in the middle field regimen. PR spectra in InAs/GaAs QDs sample was attributed to the photoreflectance response in the GaAs buffer layer. Band bending energies were calculated for laser intensities from 1 mW to 21 mW. The photoreflectance comparative study in the samples was realized considering the difference in the parameters: electric field on the surface, broadening parameter, energy gained by photoexcited carriers due to the electric field applied, frequency of light and heavy holes and band bending energy values. The results suggest that the presence of InAs quantum dots increases the light and heavy holes frequencies and the band bending energy values; and decreases the electric field on the surface, the broadening parameter and the energy gained by photoexcited carriers. We found that InAs QDs presence modifies the surface electrical field around one order of magnitude in the GaAs buffer layer and this behavior can be attributed to surface passivation.

Simultaneous Quantification of Indium and Nitrogen Concentration in InGaNAs Using HAADF-STEM

To unambiguously evaluate the indium and nitrogen concentrations in InxGa1−xNyAs1−y, two independent sources of information must be obtained experimentally. Based on high-resolution scanning transmission electron microscopy (STEM) images taken with a high-angle annular dark-field (HAADF) detector the strain state of the InGaNAs quantum well is determined as well as its characteristic HAADF-scattering intensity. The strain state is evaluated by applying elasticity theory and the HAADF intensity is used for a comparison with multislice simulations. The combination of both allows for determination of the chemical composition where the results are in accordance with X-ray diffraction measurements, three-dimensional atom probe tomography, and further transmission electron microscopy analysis. The HAADF-STEM evaluation was used to investigate the influence of As-stabilized annealing on the InGaNAs/GaAs sample. Photoluminescence measurements show an annealing-induced blue shift of the emission wavelength. The chemical analysis precludes an elemental diffusion as origin of the energy shift—instead the results are in agreement with a model based on an annealing-induced redistribution of the atomic next-neighbor configuration.

Fabrication and Characterization of GaAs Tunnel Diode and ErAs Nanoparticles Enhanced GaAs Tunnel Diode for Multijunction Solar Cell

ABSTRACTWe report here the fabrication and characterization of GaAs tunnel diode (TD) and ErAs nanoparticles (Nps) enhanced GaAs TD. Four GaAs TDs with different contact area were fabricated by using MOCVD. We found extremely high peak current density of ∼250A/cm2 for the TD with r=0.25mm contact area. Moreover a hysteresis loop was appeared during sweeping up and sweeping down the external voltage. A ‘vector load line model’ was proposed to explain the origin of the shape of the hysteresis loop and the onset of the bistability occurred at the intersect of the loadline and the current-voltage (I-V) curve of TD. Meanwhile, we have grown ErAs Nps on GaAs(100) surface by using MBE and succeeded in overgrowth of GaAs after ErAs deposition. GaAs(p+)/ErAs(Nps)/GaAs(n+) TDs were fabricated and characterized. We found the GaAs sample containing 70s deposition of ErAs showed the best TD behavior. No TD behavior was observed for the sample without addition of ErAs Nps, clearly indicating the strong tunneling enhancement effect from ErAs Nps.