M. Bürger

Single-photon emission from cubic GaN quantum dots

We report the demonstration of single-photon emission from cubic GaN/AlN quantum dots grown by molecular beam epitaxy. We have observed spectrally clean and isolated emission peaks from these quantum dots. Clear single-photon emission was detected by analyzing one such peak at 4 K. The estimated g(2)[0] value is 0.25, which becomes 0.05 when corrected for background and detector dark counts. We have also observed the single-photon nature of the emission up to 100 K (g(2)[0] = 0.47). These results indicate that cubic GaN quantum dots are possible candidates for high-temperature operating UV single-photon sources with the possibility of integration into photonic nanostructures.

Lasing properties of non-polar GaN quantum dots in cubic aluminum nitride microdisk cavities

We demonstrate laser emission from optically pumped non-polar cubic GaN quantum dots embedded in cubic aluminum nitride microdisks. Power dependent micro-photoluminescence studies at low temperature (∼10 K) revealed S-shaped curves of the integral mode intensity. We observed whispering gallery modes with quality factors up to 5000 at the high energy side (4 eV, i.e., ∼310 nm wavelength) in photoluminescence spectra of microdisks with a diameter of 2.5 μm. Furthermore, we have determined the spontaneous emission coupling factors to β = 0.12 and β = 0.42 for resonator modes of different radial orders.

Whispering gallery modes in zinc-blende AlN microdisks containing non-polar GaN quantum dots

Whispering gallery modes (WGMs) were observed in 60 nm thin cubic AlN microdisk resonators containing a single layer of non-polar cubic GaN quantum dots. Freestanding microdisks were patterned by means of electron beam lithography and a two step reactive ion etching process. Micro-photoluminescence spectroscopy investigations were performed for optical characterization. We analyzed the mode spacing for disk diameters ranging from 2-4 μm. Numerical investigations using three dimensional finite difference time domain calculations were in good agreement with the experimental data. Whispering gallery modes of the radial orders 1 and 2 were identified by means of simulated mode field distributions.

Narrow spectral linewidth of single zinc-blende GaN/AlN self-assembled quantum dots

We study by microphotoluminescence the optical properties of single self-assembled zinc-blende GaN/AlN quantum dots grown by plasma-assisted molecular beam epitaxy. As opposed to previous reports, the high quality of such zinc-blende GaN quantum dots allows us to evidence a weak acoustic phonon sideband as well as a limited spectral diffusion. As a result, we report on resolution-limited quantum dot linewidths as narrow as 500 ± 50 μeV. We finally confirm the fast radiative lifetime and high-temperature operation of such quantum dots.

Excitonic complexes in single zinc-blende GaN/AlN quantum dots grown by droplet epitaxy

We study by microphotoluminescence the optical properties of single zinc-blende GaN/AlN quantum dots grown by droplet epitaxy. We show evidences of both excitonic and multiexcitonic recombinations in individual quantum dots with radiative lifetimes shorter than 287 ± 8 ps. Owing to large band offsets and a large exciton binding energy, the excitonic recombinations of single zinc-blende GaN/AlN quantum dots can be observed up to 300 K.

Active zinc-blende III–nitride photonic structures on silicon

We use a layer transfer method to fabricate free-standing photonic structures in a zinc-blende AlN epilayer grown by plasma-assisted molecular beam epitaxy on a 3C-SiC pseudosubstrate and containing GaN quantum dots. The method leads to the successful realization of microdisks, nanobeam photonic crystal cavities, and waveguides integrated on silicon (100) and operating at short wavelengths. We assess the quality of such photonic elements by micro-photoluminescence spectroscopy in the visible and ultraviolet ranges, and extract the absorption coefficient of ZB AlN membranes (α ~ (2–5) × 102 cm−1).