Structure of GaN quantum dots grown under “modified Stranski–Krastanow” conditions on AlN

Abstract

We propose a procedure to grow GaN quantum dots (QDs) on AlN by using the Ga surfactant effect in plasma-assisted molecular beam epitaxy. Self-formed GaN islands were spontaneously generated under vacuum, after evaporation of the Ga bilayer stabilizing the two-dimensional GaN layer grown under Ga-rich conditions. Island characteristics (size and density) are studied as a function of the nominal amount of GaN deposited. We demonstrate that the QD density can be controlled in the 3×1010 cm−2–2×1011 cm−2 range. It is shown that beyond a given amount of GaN nominally deposited, there is a coexistence between elastic and plastic relaxation, with GaN islands being formed on a partially relaxed two-dimensional GaN layer thicker than two monolayers.

Step-by-step capping and strain state ofGaN∕AlNquantum dots studied by grazing-incidence diffraction anomalous fine structure

“…This resulted in the formation of a Ga bilayer at the surface inhibiting the 2D/3D transition even above the usual ∼ 2 MLs critical thickness for the 2D/3D transition in the SK growth mode [5]. The thermal evaporation under vacuum of the Ga bilayers led to the transition of the 2D GaN layer into 3D QDs [8,9] close to the Ga K-edge, and b) energy scans at fixed scattering vector (Q) corresponding to the maximum of the QDs contribution to the diffuse scattering (i.e. at the maximum of the partial structure factor F A=Ga profile extracted from the multiwavelength h-scans, see the following section and ref.…”

“…The QDs growth was achieved in the modified SK growth mode [8,9], by depositing 6 GaN monolayers (MLs)…”

“…This article focuses on the GaN/AlN system, for which the overall control of the QDs characteristics still remains a challenge. In the last few years, Molecular Beam Epitaxy (MBE) has recently been of particular interest with the improvement of QDs density control, using the Stranski-Krastanow (SK) growth mode [5,6,7] and derivatives [8,9,10]. Size homogeneization of the QDs was achieved using vertical correlation through strain fields [11,12,13].…”

Ultrafast Nonlinear Optical Response in GaN/AlN Quantum Dots for Optical Switching Applications at 1.55 μm

“…The synthesis of polar GaN/AlN QDs can be performed by two methods: either by GaN deposition under N-rich conditions or by GaN deposition under Ga-rich conditions followed by a growth interruption (Gogneau et al, 2003). N-rich growth implies a reduction of the mobility of the adsorbed species during growth that results in a high density (10 11 -10 12 cm −2 ) of small QDs (1-2 nm high).…”

Multiwavelength anomalous diffraction and diffraction anomalous fine structure to study composition and strain of semiconductor nanostructures

“…In this example [50], ≈ 6 monolayers of GaN were deposited on a buffer layer of AlN, grown on a SiC substrate, using a modified Stranski-Krastanov growth mode [62], yielding GaN quantum dots with an average height of ≈ 3 nm and a diameter of ≈ 15-20 nm. Then, several samples were grown with different thicknesses of AlN as capping layer above the GaN quantum dots, in order to study the relaxation process as a function of the capping thickness.…”