Publications
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- K. Ben Saddik, M. J. Hernández, M. A. Pampillón, M. Cervera, B. J. García
- 01 January 2025
The absorption coefficient and the energy gap of GaP1-xNx layers has been obtained by spectroscopic ellipsometry for samples grown on Si(001) substrates by chemical beam epitaxy with N mole fractions in the range 0 ≤ x ≤ 0.081. The resulting absorption spectra exhibit a direct band-like behavior near the absorption edge. The absorption coefficient values increase with the N content, reaching values in the range α ∼ 1-2×104 cm−1 in the vicinity of the absorption edge below the original GaP direct bandgap, which are comparable to those obtained for high efficiency solar cell materials. Furthermore, dependence of the absorption coefficient with increasing N content points to a strong GaP Γ-like character of the conduction-band wave function of GaP1-xNx alloys near the Brillouin zone center at k = 0, as predicted by the band anticrossing model. Bandgap energy values obtained by spectroscopic ellipsometry are compared with previous values obtained by photoluminescence measurements on the same samples, observing a shift of about 50–100 meV. Finally, the value of the band anticrossing parameter coupling the N level and the host GaP conduction band has been obtained from the dependence of both, the bandgap and the absorption coefficient, with the N content (2.1 and 3.3 eV respectively).
- K. Ben Saddik, S. Fernández-Garrido, R. Volkov, J. Grandal, N. Borgardt, B. J. García
- 20 September 2023
We investigated the chemical beam epitaxy of GaP1-xNx grown on nominally (001)-oriented Si substrates, as desired for the lattice-matched integration of optoelectronic devices with the standard Si technology. The growth mode and the chemical, morphological, and structural properties of samples prepared using different growth temperatures and N precursor fluxes were analyzed by several techniques. Our results show that, up to x ≈ 0.04, it is possible to synthesize smooth and chemically homogeneous GaP1-xNx layers with a high structural quality. As the flux of the N precursor is increased at a given temperature to enhance N incorporation, the quality of the layers degrades upon exceeding a temperature-dependent threshold; above this threshold, the growing layer experiences a growth mode transition from 2D to 3D after reaching a critical thickness of a few nm. Following that transition, the morphology and the chemical composition become modulated along the [110] direction with a period of several tens of nm. The surface morphology is then characterized by the formation of {113}-faceted wires, while the N concentration is enhanced at the troughs formed in between adjacent (113) and (113). On the basis of this study, we conclude on the feasibility of fabricating homogeneous thick GaP1-xNx layers lattice matched to Si (x = 0.021) or even with N content up to x = 0.04. The possibility of exceeding a N mole fraction of 0.04 without inducing coupled morphological–compositional modulations has also been demonstrated when the layer thickness is kept below the critical value for the 2D–3D growth mode transition.
- P. Tejedor, E. García-Tabarés, B. Galiana, L. Vázquez, B. J. García
- 15 April 2023
Linear arrays of high-quality quantum dots (QD) integrated in Si are an ideal platform in exploring the manipulation and transmission of quantum information. Understanding QD self-organization mechanisms on substrates compatible with Si technology is therefore of great practical importance. Here we demonstrate the epitaxial growth of linear arrays of InAs and InGaAs QDs from As2 and In molecular beams on bare and GaAs-coated Si(0 0 1) substrates, patterned by high-resolution laser interference nanolithography. Atomic force microscopy, in combination with high-resolution scanning and transmission electron microscopies, show that these arrays exhibit an improvement in growth selectivity, lateral order and size uniformity of the QDs when a pseudomorphic 1 nm-thick GaAs buffer layer is grown prior to InAs deposition. In addition, preferential nucleation of InxGa1-xAs QDs along the 〈1 1 0〉 -oriented edges of the nanostructured GaAs-on-Si(0 0 1) substrate results from In adatom migration from (1 1 1) to (0 0 1) nanofacets and the erosion of the wetting and buffer layers caused by the Ga-In intermixing at the step edge during the Stranski-Krastanov transition. These are key elements in the formation of linear arrays of coherent QDs, which differ in morphology and structure from those obtained on both GaAs(0 0 1) and Si(0 0 1) planar surfaces.
- K. Ben Saddik, B. J. García, S. Fernández-Garrido
- 06 December 2021
The compound GaP1-xNx is highly attractive to pseudomorphically integrate red-light emitting devices and photovoltaic cells with the standard Si technology because it is lattice matched to Si with a direct bandgap energy of ≈ 1.96 eV for x = 0.021. Here, we report on the chemical beam epitaxy of GaP1-xNx alloys on nominally (001)-oriented GaP-on-Si substrates. The incorporation of N into GaP1-xNx was systematically investigated as a function of growth temperature and the fluxes of the N and P precursors, 1,1-dimethylhydrazine (DMHy) and tertiarybutylphosphine (TBP), respectively. We found that the N mole fraction exhibits an Arrhenius behavior characterized by an activation energy of (0.79 ± 0.05) eV. With respect to the fluxes, we determined that the N mole fraction is linearly proportional to the flux of DMHy and inversely proportional to the one of TBP. All results are summarized in a universal equation that describes the dependence of x on the growth temperature and the fluxes of the group-V precursors. The results are further illustrated in a growth diagram that visualizes the variation of x as the growth temperature and the flux of DMHy are varied. This diagram also shows how to obtain single-phase and flat GaP1-xNx layers, as certain growth conditions result in chemically phase-separated layers with rough surface morphologies. Finally, our results demonstrate the feasibility of chemical beam epitaxy to obtain single-phase and flat GaP1-xNx layers with x up to about 0.04, a value well above the one required for the lattice-matched integration of GaP1-xNx-based devices on Si.
- K. Ben Saddik, A.F. Braña, N. Lopez, B. J. García, S. Fernández-Garrido
- 01 October 2021
A wide range of n- and p-type doping levels in GaAs layers grown by chemical beam epitaxy is achieved by using H2-diluted DTBSi and CBr4 as gas precursors for Si and C, respectively. We show that the doping level can be varied by modifying either the concentration or the flux of the diluted precursor. Specifically, we demonstrate carrier concentrations of 7.8 x 1017–1.4 x 1019 cm−3 for Si, and 1 x 1017–3.8 x 1020 cm−3 for C, as determined by Hall effect measurements. The dependence of Si incorporation on the diluted-precursor flux is found to be linear. In contrast, we observe a superlinear behavior for C doping. The dependence of the electron and hole mobility values on the carrier concentration as well as the analysis of the layers by low-temperature (12 K) photoluminescence spectroscopy indicate that the use of H2 for diluting DTBSi or CBr4 has no effect on the electrical and optical properties of GaAs.
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