Search

We present results of calculations and experiments on photo-current spectroscopy of modulation doped InAs self-assembled quantum dots. We derive an expression for the transition probability describing the dependence of the photo-current on the parameters of the dot, the number of carriers, and the polarization and energy of incident photons. The results of preliminary calculations are compared with experiments, which clearly show the dependence on photon energy and polarization. [Copyright &y& Elsevier]

Abstract In this work we present a new epitaxial lift-off (ELO) approach based on the use of a strained AlAs/InAlAs superlattice (SL) as sacrificial layer for InP related materials. Such an ELO process enables the fabrication and transfer of a thin active III-V heterostructure via its separation from its III-V parent substrate using selective chemical etching. The strategy is of particular interest for large area devices such as solar cells. The process studied here also allows the substrate reuse for a low-cost approach based on III-V-based device fabrication. In order to realize the ELO process on InP substrates, the main difficulty is the lack of lattice-matched materials offering the high chemical etching selectivity needed over both the substrate and the lattice-matched alloys of the active heterostructure. The present study therefore contributes effective strategy for overcoming the latter constraints. The AlAs/InAlAs SL was thus explored as a potential candidate as sacrificial layer for the InP lattice matched materials. The growth conditions of such SLs were investigated to produce low defect SLs compatible with the properties of an optimal sacrificial layer. The under-etching behavior of such SLs in a hydrofluoric acid-based solution was also studied in detail. The results show that advantageous under-etching rates, high enough for a full wafer detachment, combined with a low defect density, can be obtained with novel sacrificial layers based on such thin AlAs/InAlAs SL. Finally, the fabrication of solar cells via an active heterostructure grown over an optimized SL on a monolithic substrate and via a thin reported active heterostructure was performed. The solar cells perform well and demonstrate the suitability of such SLs as a sacrificial layer for InP related materials. Highlights • AlAs/InAlAs superlattices allow growth of thicker sacrificial layers than AlAs layers. • High under-etching rates can be obtained on low defect AlAs/InAlAs superlattices. • State of the art InGaAs solar cell performances obtained over optimized superlattice. • Fabrication of InGaAs solar cells via epitaxial lift-off is demonstrated. [ABSTRACT FROM AUTHOR]

We summarize here results of calculations and experiments on electron and valence hole states in a single pair of vertically stacked and electronically coupled InAs self-assembled quantum dots. In perfectly aligned quantum dots one can relate an electron–hole complex to a pair of entangled qubits. The information carried by individual qubit is related to the quantum dot index (isospin) of individual carrier. The quality of fabricated quantum dot molecules is identified from the exciton fine structure in a magnetic field. [Copyright &y& Elsevier]

We have performed magneto-photoluminescence spectroscopy of self-assembled In(Ga)As/GaAs single quantum dots. Both strength and orientation of the magnetic field have been varied. Symmetry of the dot structures as well as its breaking cause characteristic features in the optical spectra, which are determined by the electron–hole exchange and the Zeeman interaction of the carriers. The symmetry breaking can be either dot inherent due to geometry asymmetries or it can be obtained by applying a magnetic field with an orientation different from the dot symmetry axis. [Copyright &y& Elsevier]

The exciton states in self-assembled InAs/GaAs quantum dot molecules have been studied by optical spectroscopy and the results have been compared to detailed theoretical calculations. We demonstrate that excitons in symmetric molecule structures form entangled quantum states with the degree of entanglement controlled by tunneling and Coulomb interaction. [Copyright &y& Elsevier]

Due to Silicon (Si) material abundance and lower cost, integration of high efficiency III-V solar cells on Si substrates is of major importance for future solar energy harvesting devices. In this paper, we report on the growth optimization with a detailed characterization of epitaxial growth of crystalline GaAs on porous silicon layers (PSL), and demonstration of single-junction GaAs solar cell on PSL performances. GaAs deposition is performed on engineered porous Si surfaces with different growth temperatures. One and two-steps growth (TSG) were also investigated. X-ray diffraction demonstrated almost one order of magnitude lower threading dislocation density (TDD) of 2× 108 cm-2 for TSG process of GaAs on PSL compared to the one-step growth. Atomic Force Microscopy and Scanning Electron Microscopy showed that a reduction of growth temperature leads to surface morphology improvement. A single junction GaAs solar cell heterostructure grown by TSG and fabricated atop the porous layer, demonstrated higher open-circuit voltage (V oc) and fill factor (FF) when compared to an identical structure grown on crystalline Si (c-Si). • First GaAs solar cell demonstration on Porous Silicon Layer. • Evaluation of nanoheteroepitaxtial (NHE) growth on engineered porous Si surface. • Two-step growth for good crystalline quality GaAs layers.. • Defect density in the layers attributed principally to threading dislocations (TDs) and antiphase domains/boundaries. • Porous Silicon Layers help reduces GaAs layers strain. [ABSTRACT FROM AUTHOR]

Five stacked layers of InAs quantum dots (QDs) embedded in quaternary InGaAsP were grown on (100) InP substrate to form a laser diode. Two methods were used to achieve tuning: changing the laser cavity length or varying the temperature. Stimulated emission between ∼1.51 and ∼1.64 μm was observed depending on the cavity length and the QD barrier height. The threshold current density was decreased for longer cavities to a value as low as 49 A/cm2 at 77 K. The relation between temperature and lasing peak wavelength was measured to be ∼0.21 nm/K leading to room temperature lasing at ∼1.61 μm. [Copyright &y& Elsevier]

We discuss key issues related to quantum dot infrared photodetectors. These are the normal incidence response, the dark current, and the responsivity and detectivity. It is argued that the present devices have not fully demonstrated the potential advantages. The dominant infrared response in devices so far is polarized in the growth direction. The observed dark currents are several orders of magnitude higher than those for quantum well photodetectors; while ideally they should be lower. The areas that need improvements are pointed out. [Copyright &y& Elsevier]