Blue-light emission from GaN∕Al0.5Ga0.5N quantum dots

Abstract

The growth by molecular beam epitaxy and the optical properties of GaN∕Al0.5Ga0.5N quantum dots on (0001) sapphire substrates are reported. The quantum dots are spontaneously formed via a two dimensional to three dimensional transition upon growth interruption. Photoluminescence over the blue range (435–470nm) is obtained at room temperature by varying the GaN nominal thickness. A weak temperature dependence of the integrated photoluminescence intensity between low temperature and room temperature is observed indicating strong carrier localization in the quantum dots.

GaN/Al0.5Ga0.5N quantum dots and quantum dashes

“…Since the dislocation density is estimated to be ~3 × 10 10 cm -2 in Al 0.5 Ga 0.5 N layers [6], these large R values indicate a strong carrier localization in both the QDs and QDashes. However, R is 3 times higher for QDs than for QDashes.…”

“…3 (for F = 2.2 MV/cm and 3 MV/cm), and compared to the PL measurements obtained at 2 different excitation powers. The luminescence from the Al 0.5 Ga 0.5 N layer and the GaN wetting layer (with a thickness of ~4 MLs [6]) are also reported in the figure At a larger excitation power (1.5 mW), a fair agreement is obtained with F = 2.2 MV/cm whereas F should be increased to 3 MV/cm to be adjusted to the PL data for which the excitation power is reduced by 2 orders of magnitude (15 µW). This feature is attributed to a partial screening of the internal electric field induced by charge accumulation at the opposite sides of the nanostructure as the excitation power is increased.…”

“…The GaN/Al 0.5 Ga 0.5 N 2D-3D island formation was monitored in situ by Refection High-Energy Electron Diffraction (RHEED): similarly to a Stranski-Krastanow (S-K) growth mode, it is characterized by a change of the RHEED pattern from streaky to spotty-like (when the GaN growth is interrupted and the NH 3 flux is turned off) above a critical thickness of 6 MLs [6], to be compared to 3 MLs in the case of GaN/AlN QDs. Under these conditions QD-shaped islands are observed (Fig.…”

Fabrication of GaN quantum dots using Ga droplet epitaxy and thermal annealing by metal organic chemical vapor deposition

“…However, growing high quality GaN QDs is still a challenge. The most frequently used approach is strain-induced nucleation via StranskiKrastanov (SK) growth modes in heteroepitaxy [4][5][6], but, this method necessitates highly mismatched system and usually results in highly inhomogeneous ensembles of QDs [7,8]. In lower lattice mismatch systems, an alternative approach is Ga droplet epitaxy which is based on vaporliquid-solid (VLS) mechanism [9].…”

Recent TEM developments applied to quantum structures

“…However, electroluminescence is a challenging issue for AlN. The use of lower Al-content AlxGa1 − xN matrices is therefore an attractive alternative [3]. Although such a realization showed a great potential of GaN/(AlGaN) QDs for high-efficiency visible-light emitting devices, some fundamental issues still need further investigations, particularly the behavior of AlGaN alloy as a spacer layer in an environment where the strain-field distribution is not uniform.…”