We comparatively study the onset of photo-induced non-radiative intrinsic Auger recombination processes for red, yellow and green light emitting InGaNsingle bondGaN hetero-structures grown along the polar orientation. We find a dramatic reduction of the photo excitation densities triggering the domination of Auger effect with increasing emission wavelength; that is to say in concert with the enhancement of the internal electric field in the structure. In long wavelength emitters, the internal electric field is stronger, and hence reducing the impact of the internal electric field is more critical.

A promising route towards nanodevice applications relies on the association of graphene and transition metal dichalcogenides with hexagonal boron nitride (h-BN). Due to its insulating nature, h-BN has emerged as a natural substrate and gate dielectric for graphene-based electronic devices. However, some fundamental properties of bulk h-BN remain obscure. For example, the band structure and the position of the Fermi level have not been experimentally resolved. Here, we report a direct observation of parabolic dispersions of h-BN crystals using high-resolution angle-resolved photoemission spectroscopy (ARPES). We find that h-BN exfoliation on epitaxial graphene enables overcoming the technical difficulties of using ARPES with insulating materials. We show trigonal warping of the intensity maps at constant energy. The valence-band maxima are located around the K points, 2.5 eV below the Fermi level, thus confirming the residual p-type character of typical h-BN.

We address the intrinsic optical properties of hexagonal boron nitride in the deep ultraviolet. Weshow that the fine structure of the phonon replicas arises from overtones involving up to six low-energy interlayer shear modes. These lattice vibrations are specific to layered compounds since theycorrespond to the shear rigid motion between adjacent layers, with a characteristic energy of about6-7 meV. We obtain a quantitative interpretation of the multiplet observed in each phonon replicaunder the assumption of a cumulative Gaussian broadening as a function of the overtone index,and with a phenomenological line-broadening taken identical for all phonon types. We show fromour quantitative interpretation of the full emission spectrum above 5.7 eV that the energy of theinvolved phonon mode is 6.8±0.5 meV, in excellent agreement with temperature-dependent Ramanmeasurements of the low-energy interlayer shear mode in hexagonal boron nitride. We highlightthe unusual properties of this material where the optical response is tailored by the phonon groupvelocities in the middle of the Brillouin zone.

Two dimensional materials like graphene, transition metal dichalcogenides, and hexagonal boron nitride (h-BN) have attracted a keen interest over the past few years due to their possible integration in the next generation of nano-components. Here, we used high resolution X-ray photoemission spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) to perform a complete study of stacking configuration and identify sp3 crystal deformations of a single domain h-BN crystal. The AA′ stacking was found to best reproduce features in the experimental B and N K-edges. The NEXAFS also shows that the splitting of the 1s to π* peak in the B K-edge, recently predicted by density functional theory, may be accounted for by the presence of AB′ stacking faults. The presence of this stacking fault has, as a result, the introduction of point defects in the crystal such as boron atoms in a pyramidal or sp3 configuration. Interstitial nitrogen defects are also present in the crystal forming a N-N pair as expected for a p-type h-BN crystal.