F. Saidi

Optical anisotropy in self-assembled InAs nanostructures grown on GaAs high index substrate

We present a study of the optical properties of InAs self-assembled nanostructures grown by molecular beam epitaxy on GaAs(11N)A substrates (N = 3-5). Photoluminescence (PL) measurements revealed good optical properties of InAs quantum dots (QDs) grown on GaAs(115)A compared to those grown on GaAs(113)A and (114)A orientations substrate. An additional peak localized at 1.39 eV has been shown on PL spectra of both GaAs(114)A and (113)A samples. This peak persists even at lower power density. Supporting on the polarized photoluminescence characterization, we have attributed this additional peak to the quantum strings (QSTs) emission. A theoretical study based on the resolution of the three dimensional Schrödinger equation, using the finite element method, including strain and piezoelectric-field effect was adopted to distinguish the observed photoluminescence emission peaks. The mechanism of QDs and QSTs formation on such a high index GaAs substrates was explained in terms of piezoelectric driven atoms and the equilibrium surfaces at edges.

Optical investigation of InAs quantum dots inserted in AlGaAs/GaAs modulation doped heterostructure

Optical properties of InAs quantum dots (QDs) inserted in AlGaAs/GaAs modulation doped heterostructure are investigated. To study the effect of carrier transfer behavior on the luminescence of self-assembled quantum dots, a series of sample has been prepared using molecular beam epitaxy (Riber 32 system) in which we have varied the thickness separating the delta dopage and the InAs quantum dots layer. Photoluminescence spectra show the existence of two peaks that can be attributed to transition energies from the ground state (E1-HH1) and the first excited state (E2-HH2). Two antagonist effects have been observed, a blue shift of the emission energies result from electron transferred from the AlGaAs/GaAs heterojunction to the InAs quantum dots and a red shift caused by the quantum confined Stark effect due to the internal electric field existing In the AlGaAs/GaAs heterojunction.

Effect of carriers transfer behavior on the optical properties of InAs quantum dots embedded in AlGaAs/GaAs heterojunction

In this paper, we have investigated the optical properties of InAs quantum dots (Qds) embedded near the channel of a delta-doped AlGaAs/GaAs high electron mobility transistor. In order to study the influence of the two-dimensional electron gas (2DEG) on the luminescence of QDs, we have prepared different structures in which we varied the thickness (d) separating the interface of AlGaAs/GaAs heterojunction from the InAs quantum dot layer. Various photoluminescence (PL) behaviors are observed when d decreases. PL spectra show the existence of two peaks which can be attributed to transition energies from the ground state (E1-HH1) and the first excited state (E2-HH2). A blueshift, a decrease in the PL intensity and an increase in the full width at half maximum of the PL peaks are observed, when the InAs QDs layer is closer to the 2DEG.

Photoluminescence properties and high resolution x-ray diffraction investigation of BInGaAs/GaAs grown by the metalorganic vapour phase epitaxy method

In this paper, we report the obtention of quaternary (B)InGaAs/GaAs alloys grown by metal organic vapour phase epitaxy has been studied using high resolution x ray diffraction (HRXRD) and photoluminescence (PL) measurements. HRXRD has been achieved to determine the indium fraction (35%) incorporated into BGaAs, which shows that the strain effects have been reduced compared to the InGaAs one. Through further careful inspection, boron-indium gallium arsenic (BInGaAs) epilayer exhibits several PL peak emissions. They are associated to the exciton bond induced by the boron isoelectronic and cluster defect states. In contrast, for the BInGaAs single quantum well (SQW), we have a band to band transition mainly influenced by the confinement of electron-hole pairs in the BInGaAs well. However, the PL of BInGaAs SQW temperature-dependence has shown a localization effect due to the conduction-band modulation induced by the boron clustering in the structure. At high PL temperature, we have a band to band transition ...

Thermal transfer and interaction mechanisms of localized excitons in families of InAs quantum dashes grown on InP(001) vicinal substrate emitting near 1.55 μm wavelength

With the help of photoluminescence Spectroscopy (PLS), we have investigated the optoelectronic properties of two different families of InAs quantum dashes (QDashes) grown on misoriented InP(001) substrate with 2∘off miscut angle toward the [110] direction (2∘F type). The lowest full width at half maximum (FWHM) of the PL spectrum measured at 12 K indicates the good self organization of InAs QDashes. The weak ratio of the integrated PL measured in 12–300 K temperature range denotes the good spatial confinement of the photogenerated carriers in InAs QDashes. The fast redshift of the PL peaks energy and the anomalous decrease of the FWHM with the increase of the temperature are attributed to an efficient thermal relaxation process of photogenerated carriers in the vicinal sample. This result is highlighted with the help of theoretical modeling of the PL peak energy as a function of the temperature, using three models (Varshni, “Vina, Logothetidis and Cardona” and Passler). From experimental and theoretical results, we have evidenced the contribution of longitudinal acoustic-phonons (LA-phonons) in the PL of InAs/InP QDashes, via the deformation potential, especially in high temperatures range. We have attributed this behavior to the strained InAs/InP QDashes and/or to the topography of the vicinal InP(001) substrate which favors the presence of stepped phonons polarized along the steps. These vibrational modes can further interact with the excitons at high temperatures. The measured thermal activation energies of each family of InAs QDashes demonstrate that the InAs wetting layer act as a barrier for the thermoionic emission of photogenerated carriers. This result confirms the good spatial confinement of excitons in this sample.

Strain Effects on Optical Properties of (In,Ga)As-Capped InAs Quantum Dots Grown by Molecular Beam Epitaxy on GaAs (113)A Substrate

We have investigated the optical properties of InAs/GaAs (113)A quantum dots grown by molecular beam epitaxy (MBE) capped by (In,Ga)As. Reflection high-energy electron diffraction (RHEED) is used to investigate the formation process of InAs quantum dots (QDs). A broadening of the PL emission due to size distribution of the dots, when InAs dots are capped by GaAs, was observed. A separation between large and small quantum dots, when they are encapsulated by InGaAs, was shown due to hydrostatic and biaxial strain action on large and small dots grown under specifically growth conditions. The PL polarization measurements have shown that the small dots require an elongated form, but the large dots present a quasi-isotropic behavior.

Optical properties of B x In y Ga 1-x-y As/GaAs grown by Metal Organic Chemical Vapor deposition for solar cell

The present invention further includes a method for substantially lattice matching single-crystal III–V semiconductor layers by including boron in the chemical structure of active cells layers in multi-junction solar. Solar photovoltaic devices, i.e., solar cells, are devices capable of converting solar radiation into usable electrical energy. The energy conversion occurs as the photovoltaic-effect which occurs in a cell composed of a p-type semiconductor layer adjacent to an n-type semiconductor layer, here after referred to as p-n junction cell. Solar radiation impinging on a solar cell and absorbed by active region of semiconductor material generates electricity. Therefore, a quaternary material III–V semiconductor BInGaAs has been tested for the application in solar cells [1]. Single layer has been grown lattice matched on GaAs using Metal Organic Chemical Vapor deposition (MOCVD). Optical study has been achieved of B0.0108In0.36Ga0.062As quantum well. At room temperature (300 K) PL study has shown an asymmetric PL band is around 1.19 eV of the emission energies. Based in these experimental results, we have suggested that the band gap energies of BInGaAs QW could be adequate for active cells layers in multijunction solar.