T. Andreev

Modification of GaN(0001) growth kinetics by Mg doping

We have studied the effect of Mg doping on the surface kinetics of GaN during growth by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface of GaN, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN. The growth window is hence significantly reduced. Higher growth temperatures lead to an enhancement of Mg segregation and an improvement of the surface morphology.

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.

Morphological properties of GaN quantum dots doped with Eu

Morphological properties of Eu-doped GaN quantum dots grown by molecular beam epitaxy have been studied. Eu tends to segregate on the surface of AlN and GaN, leading to drastic changes in adatom kinetics. As a consequence, both size and density of Eu-doped GaN quantum dots strongly depend on the Eu flux used during the growth.

Polytype transition of N-face GaN:Mg from wurtzite to zinc-blende

We have investigated the polytype conversion of a GaN film from N-face wurtzite (2H) to zinc-blende (3C) structure due to Mg doping during growth by plasma-assisted molecular-beam epitaxy. Structural analysis by high-resolution transmission electron microscopy and high-resolution x-ray diffraction measurement revealed alignment of the cubic phase with the [111] axis perpendicular to the substrate surface. The optical characteristics of GaN:Mg layers are shown to be very sensitive to the presence of the cubic polytype. For low Mg doping, photoluminescence is dominated by a phonon-replicated donor-acceptor pair at ∼3.25eV, related to the shallow Mg acceptor level, accompanied by a narrow excitonic emission. For high Mg doping, the photoluminescence spectra are also dominated by a line around 3.25eV, but this emission displays the behavior of excitonic luminescence from cubic GaN. A cubic-related donor-acceptor transition at ∼3.16eV is also observed, together with a broad blue band around 2.9eV, previously...

Structural and Optical Properties of GaN Quantum Dots

Growth conditions, structural and optical properties of GaN quantum dots (QDs) grown by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value and on growth temperature, the growth mode of GaN deposited on AlN can be either of the Stranski-Krastanow or of the Frank-Van der Merwe type. It will be shown that vertical correlation results in a red shift and in a narrowing of the photoluminescence spectra. Growth of Eu-doped GaN quantum dots embedded in AlN will be described. Intense photoluminescence associated with Eu has been measured, with no GaN band-edge emission, as an evidence that carrier recombination mostly occurs through rare earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of temperature has been put in evidence, as a further confirmation of the recombination of confined carriers through Eu ion excitation.