Long-lived excitons in GaN/AlN nanowire heterostructures

Abstract

GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts.

UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

“…41 The nanowire was modeled as a hexahedral prism consisting of a 150 nm long GaN section followed by the AlN/GaN stack and capped with 150 nm of GaN. The nanodisks were defined similar as in ref 26, including the semipolar facets at the outer bottom interface of the nanodisks as sketched in Figure 1a. The geometrical dimensions were taken from STEM measurements (core radius: 20 nm, AlN shell thickness: 3 nm, nanodisk thickness: 5.3 nm, barrier thickness: 2.7 nm).…”

“…This band is assigned to emission from then GaN nanodisks embedded in AlN, since it is known that the three-dimensional confinement in the nanodisks hinders nonradiative recombination and hence leads to the persistence of the PL up to room temperature. 21,26 Independent of the temperature, an increase of the excitation power leads to an enhancement of the highenergy side of the nanodisk emission. This trend can be explained by both a saturation of the low-energy states in the nanodisks and a partial screening of the internal electric fields under high excitation densities.…”

Elastic versus Plastic Strain Relaxation in Coalesced GaN Nanowires: An X-Ray Diffraction Study

“…GaN nanowires then form spontaneously on various substrates without the need of any metal droplets that are required for many other semiconductor materials to induce the vapor-liquid-solid growth of one-dimensional nanostructures [4][5][6]. One of the distinct advantages of the spontaneous formation and subsequent uniaxial growth of GaN nanowires is the possibility to realize abrupt axial heterojunctions between different III-N compounds by simply switching the group III supply [7][8][9][10][11][12].…”

Intersubband absorption in Si‐ and Ge‐doped GaN/AlN heterostructures in self‐assembled nanowire and 2D layers

“…Recently the conductivity studies in NWs [15], and observation of screening of the internal electric fields due to Ge incorporation in NW heterostructures have been demonstrated [16].…”

“…In planar layers, Ge has demonstrated the possibility of obtaining high dopant concentrations, above the Mott density (10 −19 cm −3 ), without surface roughening or crack propagation . Recently the conductivity studies in NWs , and observation of screening of the internal electric fields due to Ge incorporation in NW heterostructures have been demonstrated .…”