Publications de Tiankai Zhu | EPFL Graph Search

Application of the PSI-NUSS Tool for the Estimation of Nuclear Data Related k(eff) Uncertainties for the OECD/NEA WPNCS UACSA Phase I Benchmark

Tiankai Zhu, Hakim Ferroukhi, Andreas Pautz, Alexander Vasiliev

At the Paul Scherrer Institute (PSI), a methodology titled PSI-NUSS is under development for the propagation of nuclear data uncertainties into Criticality Safety Evaluation (CSE) with the Monte Carlo code MCNPX. The primary purpose is to provide a complem ...

Academic Press Inc Elsevier Science2014

Comparison of Two Approaches for Nuclear Data Uncertainty Propagation in MCNPX for Selected Fast Spectrum Critical Benchmarks

Tiankai Zhu, Hakim Ferroukhi, Andreas Pautz, Alexander Vasiliev, Dimitri Rochman

Nuclear data uncertainty propagation based on stochastic sampling ( SS) is becoming more attractive while leveraging modern computer power. Two variants of the SS approach are compared in this paper. The Total Monte Carlo (TMC) method by the Nuclear Resear ...

Academic Press Inc Elsevier Science2014

One-dimensional exciton luminescence induced by extended defects in nonpolar GaN/(Al,Ga)N quantum wells

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Pierre Stadelmann, Denis Martin, Jacques Levrat, Nicolas Grandjean, Raphaël Butté, Yadira Arroyo Rojas Dasilva, Tiankai Zhu, Pierre Michel Corfdir

In this study, we present the optical properties of nonpolar GaN/(Al,Ga)N single quantum wells (QWs) grown on either a- or m-plane GaN templates for Al contents set below 15%. In order to reduce the density of extended defects, the templates have been proc ...

Institute of Physics2011

Defects in a-GaN grown on r-sapphire by hydride vapor phase epitaxy

Pierre Stadelmann, Denis Martin, Nicolas Grandjean, Tiankai Zhu

Non-polar a-GaN films grown on r-sapphire by hydride vapor phase epitaxy (HVPE) are studied using transmission electron microscopy (TEM). Despite the small lattice mismatch in a-GaN ([1 0 (1) over bar 0] similar to 1.1% and [0 00 1] similar to 16%), high d ...

2011

Exciton recombination dynamics in a-plane (Al,Ga)N/GaN quantum wells probed by picosecond photo and cathodoluminescence

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Denis Martin, Samuel Sonderegger, Nicolas Grandjean, Laurent Balet, Tiankai Zhu, Pierre Michel Corfdir

We present a combined low-temperature time-resolved cathodoluminescence and photoluminescence study of exciton recombination mechanisms in a 3.8 nm thick a-plane (Al,Ga)N/GaN quantum well (QW). We observe the luminescence from QW excitons and from excitons ...

American Institute of Physics2010

Study of the epitaxial relationships between III-nitrides and M-plane sapphire

Denis Martin, Nicolas Grandjean, Tiankai Zhu

GaN films epitaxially-grown on M-sapphire may have different orientations, either nonpolar and semipolar. In this paper, the different epitaxial relationships are investigated in details thanks to transmission electron microscopy. It is shown that these re ...

2010

Non-polar GaN epilayers and heterostructures for photonic applications

Tiankai Zhu

This PhD thesis describes the experimental study of wurtzite III-nitride semiconductors grown on non-polar crystal orientations, namely (1120) a- and (1010) m-planes. Hindered by poor material quality, they were not as extensively investigated as the polar ...

EPFL2009

M-Plane GaN Grown on m-Plane Sapphire by Hydride Vapor Phase Epitaxy

Denis Martin, Nicolas Grandjean, Tiankai Zhu

M-plane GaN epilayers have been directly grown on m-plane sapphire substrates by hydride vapor phase epitaxy using a low temperature GaN nucleation layer. The m-plane GaN surface is optically smooth and mirror-like, with rms roughness similar to 2.0 nm (5 ...

2009

Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Denis Martin, Jacques Levrat, Nicolas Grandjean, Tiankai Zhu, Jelena Ristic, Pierre Michel Corfdir

We present a detailed study of the luminescence at 3.42 eV usually observed in a-plane epitaxial lateral overgrowth (ELO) GaN grown by hydride vapor phase epitaxy on r-plane sapphire. This band is related to radiative recombination of excitons in a commonl ...

American Institute of Physics2009

In-Plane Polarities of Nonpolar Wurtzite Epitaxial Films Deposited on m- and r-plane Sapphire Substrates

Denis Martin, Nicolas Grandjean, Tiankai Zhu

The in-plane polarities of GaN and ZnO non-polar films deposited on r- and m-sapphire are compared. The polarity is unique on r-sapphire and mixed on m-sapphire because the direction on the substrate surface parallel to the wurztite c-direction is polar in ...

2009

Low-temperature time-resolved cathodoluminescence study of exciton dynamics involving basal stacking faults in a-plane GaN

Benoît Marie Joseph Deveaud, Jean-Daniel Ganière, Denis Martin, Nicolas Grandjean, Tiankai Zhu, Jelena Ristic, Pierre Michel Corfdir

Time-resolved cathodoluminescence at 27 K has been performed on a-plane GaN grown by epitaxial lateral overgrowth. We detail the relaxation and recombination mechanisms of excitons [free or bound to neutral donors, or bound to I1-type basal stacking faults ...

AIP American Institute of Physics2009

Nonpolar GaN-based microcavity using AlN/GaN distributed bragg reflector

Denis Martin, Nicolas Grandjean, Raphaël Butté, Eric Feltin, Gabriel Christmann, Tiankai Zhu

Nonpolar GaN based microcavity (MC) made of a bottom AlN/GaN distributed Bragg reflector (DBR) and a top dielectric SiO2/SiNx DBR has been fabricated on a-plane GaN template. The 13 pair AlN/GaN DBR, centered around 372 nm, exhibits a peak reflectivity of ...

2008

Blue lasing at room temperature in high quality factor GaN/AlInN microdisks with InGaN quantum wells

Jean-François Carlin, Nicolas Grandjean, Raphaël Butté, Eric Feltin, Mauro Mosca, Dobri Simeonov, Tiankai Zhu, Antonino Francesco Castiglia

The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering ga ...

2007

a-plane GaN grown on r-plane sapphire substrates by hydride vapor phase epitaxy

Denis Martin, Nicolas Grandjean, Raphaël Butté, Tiankai Zhu

Thin a-plane (1 1 2 0) GaN layers have been grown on r-plane (1 1 0 2) sapphire substrates by hydride vapor phase epitaxy (HVPE), using either a single-step high-temperature (HT) growth or a two-step growth method similar to that of metal organic vapor pha ...

2007