Excitonic recombination in epitaxial lateral overgrown AlN on sapphire

Abstract

Excitonic emission in heteroepitaxially grown aluminum nitride (AlN) with reduced defect density due to the epitaxial lateral overgrowth (ELO) of patterned AlN/sapphire templates has been investigated by photoluminescence spectroscopy and compared to AlN/sapphire and homoepitaxially grown AlN. The ELO sample exhibits small linewidths of the free exciton and two different bound exciton emission bands. The free exciton emission energy is shifted by 58.5 meV with respect to unstrained homoepitaxially grown AlN attributed to compressive strain. A donor bound exciton D0X with an exciton localization energy of 13.0–13.5 meV is dominating in the photoluminescence spectra of ELO AlN/sapphire. This D0X does not show strong phonon replica and is dominant at elevated temperatures in ELO AlN/sapphire. The optical quality of heteroepitaxial AlN is significantly improved using the ELO technique and therefore suitable for high efficiency ultraviolet light emitters.

Origin of defect luminescence in ultraviolet emitting AlGaN diode structures

“…We identify them as QW absorption and AlN buffer or quantum barrier absorption, respectively, as for this emission wavelength the crystal field splitting causes a strong reduction of TM polarized emission intensity in contrast to the absorption edge of the TE-polarized PLE excitation. 12 The energy difference between QW luminescence and absorption is in agreement with our earlier results. 24 The same result is found in sample C2, however due to lower signal to noise ratio, only the first PLE step is clearly visible, here ≈ 5.9 eV.…”

“…The selected samples were grown by metal-organic vapour phase epitaxy with (0001) orientation on different buffer/substrate combinations, containing superlattices for strain management, 9,10 AlN templates defined by epitaxial lateral overgrowth (ELO) on structured sapphire, 11 and direct growth of AlN on Al 2 O 3 . 12 Our set of samples consists of three samples emitting around 320 nm (sample series A), one sample emitting at 290 nm (sample B) and two emitting at 230 nm (series C). Samples A1 and A2 were grown on a 1.3 µm thick AlN template on sapphire with a dislocation density estimated to be 5 − 7 × 10 9 cm −2 from omega rocking curve broadening of the AlGaN (00.2) and (10.2) reflexes followed by an 80-period AlN/GaN superlattice.…”

Local surface plasmon enhanced polarization and internal quantum efficiency of deep ultraviolet emissions from AlGaN-based quantum wells

“…It is well-known that EQE depends on internal quantum efficiency (IQE) and light extraction efficiency (LEE) 3 . High density of intrinsically produced nonradiative impurities and dislocations during the growth of AlGaN materials are the major limitations for achieving high IQE 4 , 5 . And only the TE mode generated in the active layers can escape from the top and bottom surfaces when it is inside an escape cone.…”

MOVPE Growth of Smooth and Homogeneous Al0.8Ga0.2N:Si Superlattices as UVC Laser Cladding Layers

“…Both measurements contain the AlN reflection at Q z = 6.30 Å −1 in reciprocal space. The AlN is slightly compressively strained due to the growth of the ELO AlN template on sapphire substrates . The second reflection at lower Q z = 6.22–6.25 Å ‐1 originates from the 1 μm thick bulk AlGaN layer (a) and the AlGaN/AlGaN SL (b) which have an average composition of x = 0.79 ± 0.01.…”