Daniel Le Si Dang

M-Plane Core-Shell InGaN/GaN Multiple-Quantum-Wells on GaN Wires for Electroluminescent Devices

Nonpolar InGaN/GaN multiple quantum wells (MQWs) grown on the {11-00} sidewalls of c-axis GaN wires have been grown by organometallic vapor phase epitaxy on c-sapphire substrates. The structural properties of single wires are studied in detail by scanning transmission electron microscopy and in a more original way by secondary ion mass spectroscopy to quantify defects, thickness (1-8 nm) and In-composition in the wells (∼16%). The core-shell MQW light emission characteristics (390-420 nm at 5 K) were investigated by cathodo- and photoluminescence demonstrating the absence of the quantum Stark effect as expected due to the nonpolar orientation. Finally, these radial nonpolar quantum wells were used in room-temperature single-wire electroluminescent devices emitting at 392 nm by exploiting sidewall emission.

Eu locations in Eu-doped InGaN/GaN quantum dots

We report on the photoluminescence and photoluminescence excitation studies of Eu-doped wurtzite InGaN quantum dots (QDs) embedded in a GaN matrix grown by plasma-assisted molecular-beam epitaxy. The location of Eu3+ ions either in InGaN QDs or in the GaN spacing layer is assigned by comparing the different behaviors of the D05→F27 emission around 620nm under various photoexcitation energies and temperatures to those observed in Eu-doped GaN∕AlN QDs and a Eu-doped GaN thick layer.

Intraband spectroscopy of self-organized GaN/AlN quantum dots

GaN/AlN quantum dots grown by molecular beam epitaxy either on silicon (111), sapphire or 6H-SiC (0001) substrate have been investigated using photoluminescence, cathodoluminescence, Fourier transform infrared spectroscopy and attenuated total reflection spectroscopy. In-plane polarized intraband absorption is observed at energies of similar to 150 and 310 meV in GaN dots with 22 and 7.5 nm base diameter, respectively. For bigger dots, we observe three interlevel absorptions with a polarization component along the c-axis at energies ranging from 0.52 to 0.97 eV. Based on a simple 2D modelling of the confinement energies we show that the resonant absorptions involve conduction-band interlevel transitions between the electron ground state and states with one or two nodes along the c-axis and that in large dots, the internal field governs the transition energies

Spectroscopy of intraband electron confinement in self-assembled GaN/AlN quantum dots

We present a detailed analysis of inter- and intraband transitions in GaN/AIN self-organized quantum dots grown on sapphire, silicon (111) and 6H-SiC substrates. Quantum dot samples have been characterized by means of transmission electron microscopy, photoluminescence and photo-induced absorption spectroscopy. Interlevel transitions in the conduction band are observed in the 0.52-0.98 eV energy range, thus covering the telecommunication band. The s-p(z) absorption is peaked at 0.8 eV (0.52 eV) for samples with dot height of 1.5 nm (6 nm). Calculations show that in bigger dots the transition energy is governed by the value of the internal field.