C.S. Davis

Strong blue emission from As doped GaN grown by molecular beam epitaxy

Arsenic doped GaN grown by molecular beam epitaxy has been studied by room temperature photoluminescence. In addition to the wurzite band edge transition, luminescence from the cubic phase and very strong blue emission at ∼2.6 eV are observed. The intensities of the blue and the cubic band edge emissions have a power law dependence on the As2 flux. The formation of the cubic phase has been explained by the initial formation of GaAs before substitution of the As by the more reactive N. The intensity of the blue emission at room temperature of the As doped samples is more than an order of magnitude stronger than the band edge emission in undoped samples.

A study of the mechanisms responsible for blue emission from arsenic-doped gallium nitride

We have investigated the influence of the growth conditions on the intensity of blue emission at room temperature from As-doped GaN samples grown by molecular beam epitaxy. A series of As-doped GaN samples was grown at 800 °C with constant fluxes of As and gallium, but with different amounts of active nitrogen. Varying the N flux allowed us to investigate films grown from strongly Ga-rich conditions to more N-rich conditions. The blue emission increases monotonically with the nitrogen flux and is most intense in the layers grown under the most nitrogen-rich conditions. This fact suggests that As atoms incorporated into the Ga sub-lattice are responsible for the strong blue emission in As-doped GaN.

The influence of arsenic incorporation on the optical properties of As-doped GaN films grown by molecular beam epitaxy using As4 molecules

We have studied the influence of the incorporation of As on the optical properties of As-doped GaN layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) using arsenic tetramers. The doping level of arsenic was determined by secondary ion mass spectrometry. The arsenic concentration is uniform throughout the layers. There is a sub-linear dependence of the arsenic incorporation on the flux with a log-log slope of about 0.1. The photoluminescence from the As-doped GaN films consists of UV excitonic emission at 3.4 eV, UV emission at 3.2 eV and a strong blue band centred at 2.6 eV. The intensity of the blue band centred at 2.6 eV increases more rapidly with arsenic flux than the concentration of arsenic in the bulk, and has a log-log slope of about 0.49. This suggests an approximately fourth-power dependence of the intensity of the blue emission on the concentration of arsenic in the GaN films.

Temperature dependence of the miscibility gap on the GaN-rich side of the Ga-N-As system

We have investigated the temperature dependence of the transition from single phase films of GaN 1-x As x to phase separated layers, which show regions of hexagonal [0001] oriented GaN, cubic [111] oriented GaAs and hexagonal [0001] oriented GaN 1-x As x . We see a strong temperature dependence of the arsenic flux at which GaAs inclusions are first observed. Finally the intensity of blue emission observed in As-doped GaN samples decreases strongly with decreasing growth temperature.

RHEED Studies of Group III-Nitrides Grown by MBE

We report on the mechanisms giving rise to surface reconstruction for homo-epitaxial GaN grown by molecular beam epitaxy on (0001-) bulk GaN substrates. We have studied the surface reconstruction observed during growth and investigated the effects of supplying Ga and active nitrogen separately to the GaN surface. During growth we can observe a (2 × 2) reconstruction on (0001-) GaN under appropriate conditions. We have observed a (2 × 2) reconstruction on the GaN(0001-) substrates induced by supplying Ga to that surface. We have shown that the (2 × 2) surface reconstruction is stable in the presence of an active nitrogen flux at high temperature, but it disappears on cooling the GaN sample below ≈400 °C. Finally, we propose two possible growth models for GaN which can explain our RHEED data.

On the Origin of Blue Emission from As-Doped GaN

As-doped GaN films have been grown by plasma-assisted molecular beam epitaxy and their properties investigated using atomic force microscopy, X-ray diffraction and photoluminescence (PL) spectroscopy. The structural properties of the As-doped GaN films improve with increasing sample thickness. The room temperature PL is dominated by a strong blue emission band, exhibiting multiple peaks centered at 2.6 eV. The number of peaks increases monotonically with sample thickness. From this we conclude that the multiple peaks in the blue emission band of As-doped GaN samples arise mainly from optical interference effects. However, the possibility of several transitions involving As being responsible for the blue emission process cannot be excluded.

The Influence of Arsenic Incorporation on the Optical Properties of As‐doped GaN Films Grown by Molecular Beam Epitaxy Using Arsenic Tetramers

We have studied the influence of the incorporation of As on the optical properties of As-doped GaN layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) using arsenic tetramers. The doping level of arsenic was determined by secondary ion mass spectrometry. The arsenic concentration is uniform throughout the layers. There is a sub-linear dependence of the arsenic incorporation on the flux with a log-log slope of about 0.1. The photoluminescence from the As-doped GaN films consists of UV excitonic emission at 3.4 eV, UV emission at 3.2 eV and a strong blue band centred at 2.6 eV. The intensity of the blue band centred at 2.6 eV increases more rapidly with arsenic flux than the concentration of arsenic in the bulk, and has a log-log slope of about 0.49. This suggests an approximately fourth-power dependence of the intensity of the blue emission on the concentration of arsenic in the GaN films.

The Transition from Blue Emission in As‐Doped GaN to GaNAs Alloys in Layers Grown by Molecular Beam Epitaxy

The transition from As-doped GaN showing strong blue emission (∼2.6 eV) at room temperature to the formation of GaN 1-x As x alloys for films grown by molecular beam epitaxy was investigated. This study demonstrates that with increasing N to Ga ratio there is first an increase in the intensity of blue emission at about 2.6 eV and then a transition to the growth of GaN 1-x As x alloy films. Several possible models, which can explain how this might occur are presented.

Strong blue emission from GaN isoelectronically doped with arsenic

Abstract We have shown that for GaN films grown by molecular beam epitaxy, strong blue emission is observed for samples isoelectronically doped with arsenic. This blue emission is very strong and can be observed at room temperature in normal room lighting and is more than one order of magnitude stronger than the band edge emission in regular GaN films. The films were grown on sapphire substrates by plasma-assisted molecular beam epitaxy, using both As 2 and As 4 . In this paper we present detailed studies of the influence of the growth conditions including the arsenic flux, the group V:III ratio and substrate temperature on the intensity of the blue emission from arsenic doped GaN. This work suggests that GaNAs may potentially be a replacement for InGaN alloys in optical device applications.

Blue emission from arsenic doped gallium nitride

We have observed strong blue emission at room temperature from arsenic doped GaN samples grown by molecular beam epitaxy. Similar results were obtained for samples doped with both arsenic dimers and tetramers. The origin of this blue emission is discussed and a growth model proposed to account for our observations. We propose that arsenic doped GaN may be a suitable replacement for (InGa)N as the active region for blue light emitting devices.