Dynamics of bound-exciton luminescences from epitaxial GaN

Abstract

Free-and bound-exciton luminescences of GaN epitaxial layers grown by a sublimation technique on 6H-SiC substrates were investigated using time-integrated and time-resolved photoluminescence measurements at low temperatures. Lifetimes were determined for the donor-bound exciton at 3.4722 eV and for two acceptor-bound excitons with energies of 3.4672 eV and 3.459 eV. On the basis of our results we obtain an upper limit of the free-exciton oscillator strength of 0.0046 for GaN. Luminescences between 3.29 eV and 3.37 eV are identified as due to excitons deeply bound to centers located near the substrate-epilayer interface. Free excitons are captured by these centers within 20 ps.

Optical properties of wurtzite/zinc-blende heterostructures in GaN nanowires

“…18,[27][28][29] However, the attribution of the narrow peaks in the 3.1 eV-3.42 eV range to DAP seems to be inappropriate in the present case. The DAP emission is indeed characterized by a very different spectral shape in GaN thin film and nanowire samples, 18,25,26,28,29 where the two dominant emissions are at 3.21 eV and 3.27 eV and are significantly broader than the features found in the present samples.…”

“…We suppose that these peaks with reduced blueshift might be related to a different mechanism, such as recombination of an exciton localized at a defect or a donoracceptor pair (DAP) transition. Indeed, it should be noticed that the spectral interval where the narrow peaks appear in the present samples overlaps with the DAP band in WZ and ZB GaN (E $ 3.0-3.3 eV), 10,25,26 which has also been reported in nanowires. 18,[27][28][29] However, the attribution of the narrow peaks in the 3.1 eV-3.42 eV range to DAP seems to be inappropriate in the present case.…”

“…This behavior is not expected for DAP transitions, which either give rise to several broad peaks or to a continuous broad band. 25,26 The intensity of the emission lines is determined both by the oscillator strength of the corresponding transition and by the number of the cubic inclusions with the given thickness in the nanowire. However, it must be kept in mind that other effects can influence the transition intensity and energies.…”

Fabrication of p-type porous GaN on silicon and epitaxial GaN

“…As expected from Mg acceptors in doped GaN, we find the longitudinal optical (LO) phonon replicas at 3.18 and 3.19 eV at 150 and 11 K, respectively, with several harmonics observable at 11 K, indicating that the electronic quality of the doped GaN crystals directly on Si matches that of epitaxially grown pdoped GaN. 25 Yellow luminescence (YL) in n-GaN is normally attributed to point defect Ga vacancies, impurities, such as oxygen and carbon. 26 YL is also present in Mg-doped GaN, as observed in Figure 3(e).…”

Formation and dissociation of hydrogen-related defect centers in Mg-doped GaN

“…3). First, the intensity of the 3.27 eV DAP decreased exponentially with irradiation time, second, a deeper emission band centered at around 3.05 eV (for an excitation density of E b =2.5 keV and I b =0.14 nA) emerged and third, the weak emission line, centered at approximately 3.37 eV and tentatively assigned to excitons deeply bound to centers located in structurally disturbed regions of GaN [18], is completely quenched as a result of the electron exposure. These effects are illustrated in the lower part of Fig.…”