C. Bru-Chevallier

Current deep level transient spectroscopy analysis of AlInN/GaN high electron mobility transistors: Mechanism of gate leakage

In order to assess possible mechanisms of gate reverse-bias leakage current in AlInN/GaN high electron mobility transistors (HEMTs) grown by metalorganic chemical-vapor deposition on SiC substrates, temperature-dependent current-voltage measurements combined with Fourier transform current deep level transient spectroscopy (FT-CDLTS) are performed in the temperature range of 200–400 K. In this range of temperature reverse-bias leakage current flow is found to be dominated by Poole–Frenkel emission. Based on CDLTS measurements, a model of leakage current transport via a trap state located at the AlInN/metal interface with an activation energy of 0.37 eV is suggested. The trap nature is shown to be an extended trap, most probably associated with dislocations in the AlInN barrier layer.

Excitonic properties of wurtzite InP nanowires grown on silicon substrate

In order to investigate the optical properties of wurtzite (Wz) InP nanowires grown on Si(001) by solid source molecular beam epitaxy with the vapour-liquid-solid method, the growth temperature and V/III pressure ratio have been optimized to remove any zinc-blende insertion. These pure Wz InP nanowires have been investigated by photoluminescence (PL), time-resolved PL and PL excitation. Direct observation of the second and third valence band in Wz InP nanowires using PL spectroscopy at high excitation power have been reported and, from these measurements, a crystal field splitting of 74 meV and a spin-orbit interaction energy of 145 meV were extracted. Based on the study of temperature-dependent optical properties, we have performed an investigation of the thermal escape processes of carriers and the electron-phonon coupling strength.

Growth temperature dependence of exciton lifetime in wurtzite InP nanowires grown on silicon substrates

InP nanowires grown on silicon substrate are investigated using time-resolved spectroscopy. A strong modification of the exciton lifetime is observed (from 0.11 to 1.2u2009ns) when the growth temperature is increased from 340u2009°C to 460u2009°C. This strong dependence is not related to the density of zinc-blende insertions in the wurtzite nanowires or to the wurtzite exciton linewidth. The excitation power dependence of the lifetime and linewidth is investigated, and these results allow us to interpret the growth temperature dependence on the lifetime as a consequence of the reduction of the surface recombination velocity with the growth temperature.

Wurtzite InP/InAs/InP core–shell nanowires emitting at telecommunication wavelengths on Si substrate

Optical properties of wurtzite InP/InAs/InP core-shell nanowires grown on silicon substrates by solid source molecular beam epitaxy are studied by means of photoluminescence and microphotoluminescence. The growth conditions were optimized to obtain purely wurtzite radial quantum wells emitting in the telecom bands with a radiative lifetime in the 5-7 ns range at 14 K. Optical studies on single nanowires reveal that the polarization is mainly parallel to the growth direction. A 20-fold reduction of the photoluminescence intensity is observed between 14 and 300 K confirming the very good quality of the nanowires.

Optically active defects in an InAsP/InP quantum well monolithically grown on SrTiO3(001)

The optical properties of an InAsP/InP quantum well grown on a SrTiO3(001) substrate are analyzed. At 13 K, the photoluminescence yield of the well is comparable to that of a reference well grown on an InP substrate. Increasing the temperature leads to the activation of nonradiative mechanisms for the sample grown on SrTiO3. The main nonradiative channel is related to the thermal excitation of the holes to the first heavy hole excited state, followed by the nonradiative recombination of the carriers on twins and/or domain boundaries, in the immediate vicinity of the well.

Extraction of ultraviolet emitting silicon species from strongly hydrogenated nanoporous silicon

Ultraviolet emitting silicon species were extracted from strongly hydrogenated porous silicon nanostructures. Their photoluminescence spectra depend on size distribution of the species and can be tuned by centrifugation. Molecular structure of the extracted Si species is assumed to be very similar to some kinds of polysilanes which were theoretically described earlier by Allan et al. [Phys. Rev. B 48, 7951 (1993)]. Absence of photoluminescence signal coming from the polysilanes in the initial porous nanostructures is supposed to be due to the competitive absorption and to the energy transfer between the polysilanes and Si red emitting porous nanoparticles.

Polarization properties of single and ensembles of InAs/InP quantum rod nanowires emitting in the telecom wavelengths

The absorption and emission polarization properties of InAs quantum rods embedded in InP nanowires (NWs) are investigated by mean of (micro-)photoluminescence spectroscopy. It is shown that the degree of linear polarization of emission (0.94) and absorption (0.5) of a single NW can be explained by the photonic nature of the NW structure. Knowing these parameters, optical properties of single NWs and ordered ensembles of these NWs can be correlated one to another via proposed model, so that polarization properties of NWs can be studied using ordered ensembles on as-grown samples. As an example, the polarization anisotropy is investigated as a function of the excitation wavelength on a NW ensemble and found to be in agreement with theoretical prediction.

Temperature dependence of optical properties of InAs/GaAs self-organized quantum dots

Self-organized InAs/GaAs quantum dots (QDs) were grown by molecular beam epitaxy. The photoluminescence, its power, and temperature dependences have been studied for the ensembles of InAs QDs embedded in GaAs matrix to investigate the interband transition energies. Theoretical calculations of confined electron (heavy-hole) energy in the InAs/GaAs QDs have been performed by means of effective mass approximation, taking into account strain effects. The shape of the InAs QDs was modeled to be a convex-plane lens. The calculated interband transition energies were compared with the results of the photoluminescence spectra. The calculated interband transition energy from the ground electronic subband to the ground heavy-hole state was in reasonable agreement with the transition energy obtained by the photoluminescence measurement.

Surface Fermi level in GaAsSb structures grown by molecular beam epitaxy on InP substrates

Photoreflectance (PR) spectroscopy is performed to investigate the Fermi level pinning at the surface of GaAsSb, in a series of epitaxial structures with different Sb concentration. PR spectra exhibit Franz–Keldysh oscillations, originating from the built-in electric field in the GaAsSb layer. Experimental results indicate that the surface Fermi level is pinned in the lower half bandgap. The surface Fermi level is determined versus the Sb concentration between 38% and 52%.

Strain dependence of the direct energy bandgap in thin silicon on insulator layers

Photoreflectance spectroscopy is applied on tensilely strained silicon on insulator (sSOI) thin layers in order to evaluate the biaxial strain effect on the Si direct bandgap. The measured redshift of the E0 transition (i.e. direct bandgap) with strain (~ − 100u2009meV/%) corresponds to theoretical predictions. The hydrostatic and valence band deformation potential constants for E1 (i.e. transition close to the L point along the Λ-direction) are also measured: and .