Publications de Mehran Shahmohammadi

Temperature Dependent Exciton Funnel Dynamics in Uniform Strain Gradient Field Observed by Time-Resolved Photoluminescence

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Gwénolé Jean Jacopin, Mehran Shahmohammadi

Elastic strain engineering is an important way to reversibly tune the properties of micro/nanoscale semiconductors for promising applications in the emerging advanced nanotechnologies, such as the strain enhanced high-mobility transistors, nanogenerators, ...

WILEY-V C H VERLAG GMBH2021

Enhancement of Auger recombination induced by carrier localization in InGaN/GaN quantum wells

Nicolas Grandjean, Benoît Marie Joseph Deveaud, Raphaël Butté, Gwénolé Jean Jacopin, Wei Liu, Georg Rossbach, Lise Lahourcade, Mehran Shahmohammadi

The origin of efficiency droop in state-of-the-art quality In GaN/GaN and GaN/AlGaN quantum wells (QWs) grown on various crystal planes is studied by means of time-resolved photoluminescence spectroscopy associated with a precise determination of the QW ca ...

Amer Physical Soc2017

Excitonic Diffusion in InGaN/GaN Core–Shell Nanowires

Hua Zhang, Jean-Daniel Ganière, Gwénolé Jean Jacopin, Mehran Shahmohammadi

We report on the direct observation of the diffusion of carriers in graded InGaN/GaN quantum wells in a nanowire. By probing the local dynamics at the nanoscale, along the wire for different temperatures between 4 and 250 K, we conclude that this diffusion ...

American Chemical Society (ACS)2016

Ultrafast spectroscopy of wide bandgap semiconductor nanostructures

Mehran Shahmohammadi

Group III-nitrides have been considered a promising choice for the realization of optoelectronic devices since 1970. Since the first demonstration of the high-brightness blue light-emitting diodes (LEDs) by Shuji Nakamura and coworkers, the fabrication of ...

EPFL2015

Exciton hopping probed by picosecond time-resolved cathodoluminescence

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Gwénolé Jean Jacopin, Mehran Shahmohammadi

The exciton transport is studied in high quality ZnO microwires using time resolved cathodoluminescence. Owing to the available picosecond temporal and nanometer spatial resolution, a direct estimation of the exciton average speed has been measured. When r ...

American Institute of Physics2015

Biexcitonic molecules survive excitons at the Mott transition

Nicolas Grandjean, Jean-François Carlin, Benoît Marie Joseph Deveaud, Raphaël Butté, Jacques Levrat, Eric Feltin, Jean-Daniel Ganière, Gwénolé Jean Jacopin, Georg Rossbach, Mehran Shahmohammadi

When the carrier density is increased in a semiconductor, according to the predictions of Sir Nevil Mott, a transition should occur from an insulating state consisting of a gas of excitons to a conductive electron-hole plasma. This crossover, usually refer ...

Nature Publishing Group2014

Exciton Drift in Semiconductors under Uniform Strain Gradients: Application to Bent ZnO Microwires

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Gwénolé Jean Jacopin, Mehran Shahmohammadi, Ji Feng

Optimizing the electronic structures and carrier dynamics in semiconductors at atomic scale is an essential issue for innovative device applications. Besides the traditional chemical doping and the use of homo/heterostructures, elastic strain has been prop ...

American Chemical Society2014

Hopping process of bound excitons under an energy gradient

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Gwénolé Jean Jacopin, Mehran Shahmohammadi

We report on the mechanism of hopping for bound excitons under an energy gradient. By means of a Monte-Carlo simulation, we show that this mechanism explains the movement of bound excitons observed experimentally. We show that the speed of the excitons dec ...

American Institute of Physics2014

Temperature-Dependence of Exciton Radiative Recombination in (Al,Ga)N/GaN Quantum Wells Grown on a-Plane GaN Substrates

Nicolas Grandjean, Benoît Marie Joseph Deveaud, Etienne François Olivier Giraud, Jean-Daniel Ganière, Pierre Michel Corfdir, Mehran Shahmohammadi

This article presents the dynamics of excitons in a-plane (Al,Ga)N/GaN single quantum wells of various thicknesses grown on bulk GaN substrates. For all quantum well samples, recombination is observed to be predominantly radiative in the low-temperature ra ...

Japan Society of Applied Physics2013