K.P. Korona

Luminescence and reflectivity in the exciton region of homoepitaxial GaN layers grown on GaN substrates

Abstract In this work we report results of photoluminescence (PL) and reflectivity measurements in the exciton region of GaN homoepitaxial layers grown by metalorganic chemical vapour deposition on GaN substrates. At low temperature (4.2K), very narrow (FWHM = 1.0meV) PL lines related to excitons bound to neutral acceptor (3.4666eV) and neutral donor (3.4719eV) were observed. The energies of free excitons from reflectivity and PL measurements were found to be: E A = 3.4780eV, E B = 3.4835eV and E C = 3.502eV.

Exciton region reflectance of homoepitaxial GaN layers

Reflection measurements in the exciton region of GaN homoepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) on GaN single crystals are reported. At low temperature (4.2 K) three free exciton lines have been found with energies; EA=3.4776 eV, EB=3.4827 eV, and EC=3.502 eV. The spin‐orbit parameter Δso=19.7±1.5 meV and the crystal field parameter Δcr=9.3±0.3 meV have been obtained. From temperature dependence of exciton spectra the energy gap dependence has been found: E(T)=E(0)−λ/[exp(β/T)−1] (λ=0.121 eV, β=316 K).

Excitation mechanisms of individual Cd Te ∕ Zn Te quantum dots studied by photon correlation spectroscopy

Systematic measurements of auto- and cross-correlations of photons emitted from individual

Photoluminescence study and structural characterization of p-type ZnO doped by N and/or As acceptors

\mathrm{Cd}\mathrm{Te}∕\mathrm{Zn}\mathrm{Te}

Tunable GaN/AlGaN ultraviolet detectors with built-in electric field

quantum dots under pulsed excitation were used to elucidate nonresonant excitation mechanisms in this self-assembled system. Memory effects extending over a few excitation pulses have been detected in agreement with previous reports and quantitatively described by a rate equation model, fitting a complete set of correlation and PL intensity results. The important role of single carrier trapping in the quantum dot was established. An explanation was suggested for the unusually wide antibunching dip observed previously in

Structural and Optical Properties of Homoepitaxial GaN Layers

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Ultrafast carrier trapping in high energy ion implanted gallium arsenide

autocorrelation experiments on quantum dots under cw excitation.

Impurity-Related Luminescence of Homoepitaxial GaN Studied with High Magnetic Fields

ZnO doped with N and/or As layers was fabricated by thermal oxidation of ZnTe films grown by MBE on different substrates. Hall effect measurements demonstrated p-type conductivity with a hole concentration of ~5 × 1019 cm−3 for ZnO:As and ZnO:As:N on GaAs substrates and ~6 × 1017 cm−3 for ZnO:N on ZnTe substrates. The concentration of N and As atoms in ZnO is estimated to be ~1020 cm−3. This suggested that simple substitutional N atoms form acceptor impurities with a smaller efficiency than an As-related complex, probably AsZn–2VZn. In particular, we were able to distinguish between nitrogen and arsenic acceptor-related luminescence. Optical studies showed meaningful differences of the PL features in samples with different acceptors, grown on different substrates.

Effects of defect scattering on the photoluminescence of exciton-polaritons in n-GaN

We present the optical and the electrical properties of GaN/AlGaN structures that can be used as tunable ultraviolet photodetectors. The photosensitivity spectrum of the structures can be tuned in the range 3.5–3.85 eV by external voltage. The photosensitivity of the sample in the 3.5 eV spectral range increases about 500 times when the reverse bias changes from −2 to −6 V. The effect can be explained by changes in the electric field in the GaN/AlGaN structure. The field is generated by the internal electric polarization and the external bias. We present also a numerical modeling of the electric field, the potential profiles, and the current flow in such structures. Our modeling shows that at low bias a two-dimensional (2D)-electron gas at the AlGaN/GaN interface screens the electric field generated by spontaneous polarization. The lack of the field stops transport of photoexcited holes. The holes that are accumulated on the interface causes fast electron recombination and reduces photocurrent. The extern...

Growth by molecular beam epitaxy and properties of inclined GaN nanowires on Si(001) substrate

The review of structural and optical properties of homoepitaxial layers grown by MOVCD on single crystals GaN substrates is presented. The TEM technique is used to characterise the structural properties of epi-layers. It is found that the structural properties of GaN homoepitaxial layers are determined by the polarity of the substrate surface on which the growth takes place. It is shown that threading dislocations are present only in the layers grown on the [0001] “smooth” surface. On the other hand the layers grown on the [0001] “rough” surface are free from vertical defects. The characteristic feature of the growth on the “rough” surface are pinholes. The optical properties of homoepitaxial layers are predominantly determined by the growth polarity as well. It is shown also that the reflectivity measurement is the most precise way to determine the exciton energies and that emissions due to free excitons are strongly affected by polariton effects.