Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

Abstract

In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9× 1020cm−3 and 1 × 1020cm−3, respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 1017cm−3, the nanowires are depleted of charge carriers, whereas they become highly conductive above 1019cm−3.

UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

“…14,33 However, the surface states should not affect the conductivity of the highly doped GaN nanodisks, where the band bending is restricted to a few nanometers close to the surface. 34 The persistent phenomena are rather associated to the stem/cap GaN segments, which are fully depleted in the dark and where a conductive channel is opened under illumination. The decelerated discharging of surface states should thus delay the restoration of full depletion of these parts of the structure.…”

Surface passivation and self-regulated shell growth in selective area-grown GaN–(Al,Ga)N core–shell nanowires

“…Lefebvre et al have reported a strong influence on the PL intensity of bare GaN NWs under different atmospheres. 13 In particular, 20 The growth parameters applied for NWs on diamond are equivalent to those on Si substrate. However, GaN NW growth on diamond is characterized by a slightly thicker diameter of the NWs compared to NWs on Si due to an enhanced lateral growth (SEM images in Fig.…”

GaN nanowires on diamond

“…While substrate and dopant Si could not be separated, extremely high Mg concentrations were determined in the NWs by secondary ion mass spectrometry (SIMS). With diamond substrates, it was possible for the first time to perform SIMS measurements without an interfering influence of the substrate [59].…”

“…A brief summary of surface segregation will be given in the following whereas readers are referred to Ref. [59] for more information about the other effects.…”

“…8a where a depth of zero corresponds to the NW tip and no significant axial gradient is observed [59]. To compare the absolute doping concentration, a standard GaN:Si thin film reference on c-plane sapphire with incremented Si doping sections is included.…”