V
P
Last name: VALVIN
First name: Pierre
International audience
We have investigated a series of samples embedding ZnO/(Zn,Mg)O quantum wells of different sizes, in wurtzite phase, by using time-resolved photoluminescence. The samples were grown by molecular beam epitaxy on ZnO templates, themselves deposited on sapphire substrates. The presence of large internal electric fields in these quantum wells...
Properties of self-assembled quantum dots (QDs), often referred to as artificial atoms in solid state, are very interesting in order to study physical effects specific to single quantum systems such as the single-photon emission. Thanks to their huge vertical quantum confinement, GaN QDs are emitting even at room temperature and on a large UV...
Properties of self-assembled quantum dots (QDs), often referred to as artificial atoms in solid state, are very interesting in order to study physical effects specific to single quantum systems such as the single-photon emission. Thanks to their huge vertical quantum confinement, GaN QDs are emitting even at room temperature and on a large UV...
We use the intense, 5-ns-long, excitation pulses provided by the fourth harmonic of a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser to induce a strong high-energy shift of the photoluminescence of a 7.8-nm-wide GaN/Al0.15Ga0.85N single quantum well. We follow the complex relaxation dynamics of the energy and of the intensity of this...
We study by time resolved photoluminescence (TRPL) low N and In content GaInNAs (GINA) alloy layers grown by molecular beam epitaxy on GaAs substrate. The TRPL experiments show the coexistence and the carrier exchanges between bound- and free-exciton states, in this kind of alloy. Temperature dependent experiments demonstrate the thermal...
In this work, we investigate the impact of the quantum confined Stark effect and of the carrier localization on the internal quantum efficiency of polarized single or multiple InxGa1-xN/GaN quantum well(s), and semi-polar (11e22) multiple InxGa1-xN/InyGa1-yN quantum well. We find that increasing the influence of the quantum confined Stark...
The time dependence of the photoluminescence of GaN/AlN quantum dots (QD's) after high photoexcitation is examined on a large time scale. A continuous change in energy peak is reported, resulting in a giant energy shift of more than 1 eV after delays of several hundreds of microseconds. Simultaneously, the intensity decreases over more than...
The variation of the internal quantum efficiency (IQE) of single InGaN quantum well structures emitting from blue to red is studied as a function of the excitation power density and the temperature. By changing the well width, the indium content, and adding a strain compensation AlGaN layer, we could tune the intrinsic radiative recombination...
InGaN/GaN single quantum wells were grown by molecular beam epitaxy on the silicon substrate onto thin AlN and GaN buffer layers. The InGaN/GaN structure is porosified using a combination of Si x N y nanomasking and sublimation and compared with a non-porous reference. The photoluminescence efficiency at room temperature of the porosified...
The Auger effect and its impact on the internal quantum efficiency (IQE) of yellow light emitters based on silicon-doped InGaN–AlGaN–GaN quantum wells are investigated by power dependence measurement and using an ABC model. Photoluminescence intensity recorded as a function of excitation power density follows a linear dependence up to a...
We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Yoshiya Iwata, Ryan G. Banal, Shuhei Ichikawa, Mitsuru Funato, and Yoichi Kawakami, Journal of Applied Physics 117,...
In group-III nitride quantum wells, indirect excitons (IXs) are naturally formed because the electron-hole pair is separated along the growth (0001) axis by strong internal electric fields. These IXs therefore exhibit strong permanent dipole moments and extremely long radiative lifetimes (> 10µs). Previous extensive studies of IXs in...
International audience
We investigate the optical properties of porous GaN films of different porosities, focusing on the behaviors of the excitonic features in time-integrated and time-resolved photoluminescence. A substantial enhancement of both excitonic emission intensity and recombination rate, along with insignificant intensity weakening under temperature rise,...
Excitons in nitride quantum wells (QWs) are naturally indirect due to the strong internal electric field: electron and hole within such excitons are spatially separated, leading to strong dipole moments and long radiative lifetimes. The physics of indirect excitons (IXs) has been extensively studied in GaAs-based heterostructures: they can...
Excitons in wide nitride Quantum Wells (QWs) are naturally indirect due to the strong internal electric field: within such excitons the electron and the hole are spatially separated, resulting in strong dipole moments and long radiative lifetimes. These properties offer the possibility to explore the collective exitonic phases with complex...
Light emission in polar group-III nitride quantum wells (QWs) optically pumped at densities significantly below the lasing threshold is usually interpreted in terms of excitons. Whereas thin GaN QWs with fast radiative lifetimes are employed in light-emitting devices, the excitons in thick QWs (typ. 7nm) are characterized by a non-zero dipole...
We investigate the transport of dipolar indirect excitons along the growth plane of polar (Al,Ga)N/GaN quantum well structures by means of spatially and time-resolved photoluminescence spectroscopy. The transport in these strongly disordered quantum wells is activated by dipole-dipole repulsion. The latter induces an emission blue shift that...
Piezoelectric effects on the optical properties of GaN/AlN quantum dots have been investigated by both continuous-wave and time-resolved photoluminescence (TRPL) measurements. The increase in excitation density in CW-PL leads to a blue shift of the transition energy. The TRPL measurements reveal a very large blue-shift (0.6 eV) of the PL peak...
International audience
No description
Continuous-wave, time-integrated, and time-resolved photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO/Zn0.78Mg0.22O quantum wells of varying widths. By comparing experimental results with a variational calculation of excitonic energies and oscillator strengths, we determine the magnitude...
Time-resolved photoluminescence spectra of orange light emitting (Ga,In)N-based devices have been grown by metal-organic vapour phase epitaxy on C plane sapphire for indium compositions ranging up to 23 percents. The temperature dependent time resolved photoluminescence spectra collected through the 8K-300K range are found to exhibit behaviours...
Excitons in nitride quantum wells (QWs) are naturally indirect due to the strong built-in electric field: electron and hole within such excitons are spatially separated, leading to strong dipole moments and long radiative lifetimes. The physics of indirect excitons (IXs) has been extensively studied in GaAs-based heterostructures: they can...