Two-layer photo-thermal deflection model to study the non-radiative recombination process: Application to Ga0.7In0.3As0.23Sb0.77/GaSb and Al0.3Ga0.7As0.08Sb0.92/GaSb laser structures

International audiencePhoto-thermal deflection technique is used to study the nonradiative recombination process in laser structures Ga0.7In0.3As0.23Sb0.77 and Al0.7Ga0.3As0.08Sb0.92 grown by molecular beam epitaxy on GaSb substrate. A two layer theoretical model has been developed, taking into account both thermal and electronic contributions in the photothermal signal; the coincidence between experimental curves giving the normalized amplitude and phase variations versus square root modulation frequency to the corresponding theoretical ones permits to determine non-radiative lifetime, electronic diffusivity, and surface and interface recombination velocities

New Photothermal Deflection Method to Determine Thermal Properties of Bulk Semiconductors

5th International Conference on Diffusion in Solids and Liquids (DSL-2009)International audienceIn this paper, we present a new Photothermal Deflection Technique (PTD) to determine thermal properties of bulk doped or undoped semiconductor such as GaAs, GaSb, InAs, etc. The method proposed here consists in covering the sample with a thin graphite layer in order to increase the photothermal signal and to ovoid any reflection on the sample surface. This method deals with the analysis of the logarithm of amplitude and phase variation of the photothermal signal versus square root modulation frequency where the sample placed in air is heated by a modulated light beam coming from a halogen lamp. So the best coincidence between experimental curves and corresponding theoretical ones gives simultaneously the best values of thermal conductivity and thermal diffusivity of the sample. These obtained values are in good agreement with those found in literature. The advantage of applying this method in this way lies in its simplicity and its sensibility to both thermal conductivity and thermal diffusivity

Investigation of electrical and optothermal properties of Si-doped GaSb epitaxial layers by the Hall effect, PL measurement and photothermal deflection spectroscopy

International audienceThe aim of this work is to investigate the influence of Si-doping on the optical, thermal and electrical properties of GaSb epitaxial layers. Such an influence was quantified through photoluminescence (PL), mirage effect (photothermal spectroscopy) and Hall effect measurements. Several GaSb samples, grown by Molecular Beam Epitaxy (MBE) on (100)-oriented GaAs semiinsulating substrates, with different Si-doping levels ranging from 4.95E16 at.cm-3 up to 8.11E19 at.cm-3 were tested. As a comparison, the same measurements were also performed on a GaSb non intentionally doped layer. The Hall effect data shows a monotonic decrease in carrier mobility when the hole concentration increase. The effect of band-to-band, band-impurity transitions on the PL gap E0 and the influence of high impurity concentration on the PL and absorption spectra have been also studied. Finally, the optical absorption changes induced by Si-doping on GaSb samples were investigated by photothermal deflection. It was shown that this technique allows a very precise deduction of the real interband gap energy of a semiconductor material as GaSb. Thermal conductivities were also deduced from the photothermal deflection measurements. The found values are very low due to the thermal resistivity of the layer-substrate interface but also due to the lattice-mismatch between GaSb epilayers and the GaAs substrate. However, the contribution of the free carriers to the thermal conductivity, with a high p-doping level (p>10E19 cm-3), could be highlighted

Improvement of carriers diffusion length and mobility in annealed GaAsPN materials for intermediate band solar cells.

International audienceIn this paper, we investigate the effect of thermal annealing on nonradiative recombination parameters ofGaAsPN materials used for intermediate band solar cells. This study is performed thanks to photothermaldeflection technique PTD. Indeed, nonradiative lifetime, electronics diffusivity, surface and interface recombination,are extracted through a good fit between theoretical and experimental amplitude and phase of PTDsignal. Then, the effects of annealing temperature on charge transport were analyzed and discussed. As animportant result for solar cells improvement, we have found that hole diffusion length and mobility increasesrespectively from 13.8 to 19 (+/-2.5%) μm and from 112 (+/-4.9%) to 153 (+/-3.5%) cm2/V⋅s for GaAsPN as grown tothat annealed at 800 °C

Determination of free-carrier and phonon-assisted absorptions for Si-doped GaSb thin layers

International audiencePhotothermal deflection spectroscopy is used in order to investigate near- and sub-band gap absorption of Si-doped GaSb epilayers deposited by MBE on a semi-insulating GaAs substrate. The optical absorption spectra show an extra absorption on the transparency region below the bandgap due to free-carrier absorption. However, for energies above the gap, we notice a linear behavior of the square root of the absorption coefficient versus the heating beam energy, which is attributed to phonon-assisted absorption. From interpolation of the phonon absorption to low energies we have determined the free-carrier absorption that is found to follow the Drude law

Paraffin oil thermal diffusivity determination using a photothermal deflection setup with a 2.3μm pump: a first step towards methane detection

International audienceThe photothermal deflection technique, also known as "mirage effect", is a nondestructive method of evaluating thermal properties of solid, liquid or gaseous species. This technique will be used to detect pollutant absorption. As the deflection is stronger in liquids than gases, we will first consider the deflection in paraffin oil. We consider a medium that is heated by a modulated laser diode beam, and we measure the deflection of the probe beam passing through the heated region as a function of the distance between the axes of the beams. After some theoretical considerations and numerical simulations, we present the application of this method to the experimental determination of the thermal diffusivity of a liquid sample in excellent agreement with previously known values