UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

Abstract

We have characterized the photodetection capabilities of single GaN nanowires incorporating 20 periods of AlN/GaN:Ge axial heterostructures enveloped in an AlN shell. Transmission electron microscopy confirms the absence of an additional GaN shell around the heterostructures. In the absence of a surface conduction channel, the incorporation of the heterostructure leads to a decrease of the dark current and an increase of the photosensitivity. A significant dispersion in the magnitude of dark currents for different single nanowires is attributed to the coalescence of nanowires with displaced nanodisks, reducing the effective length of the heterostructure. A larger number of active nanodisks and AlN barriers in the current path results in lower dark current and higher photosensitivity, and improves the sensitivity of the nanowire to variations in the illumination intensity (improved linearity). Additionally, we observe a persistence of the photocurrent, which is attributed to a change of the resistance of the overall structure, particularly the GaN stem and cap sections. In consequence, the time response is rather independent of the dark current.

Effect of the nanowire diameter on the linearity of the response of GaN-based heterostructured nanowire photodetectors

“…Following the interpretation for the case of a single AlN insertion [20], the reverse current is associated to a leakage path through the barriers, involving a GaN shell, surface conduction or the coalescence of multiple wires [10]. Under forward bias, among the set of nanowires under study, we observe a strong dispersion of the dark current, varying from a few nanoamperes to microamperes at +1 V bias.…”

“…Nanowire photoconductors are characterized by high photocurrent gains, which can reach 10 6 , and strong spectral contrast above and below the bandgap. A general feature in nanowire photoconductors is the fact that the photocurrent scales sublinearly with the impinging laser power, which has been shown for single GaN nanowires regardless of the presence of heterostructures [6][7][8][9][10], as well as for nanowires of other material systems such as ZnTe [11], ZnO [12,13], InP [14], CuO [15], and GaAs [16]. This sublinearity of the response hampers the use of such devices for quantification of the radiant fluence, and restricts their application domain to digital detection.…”

Long-range ordered vertical III-nitride nano-cylinder arrays via plasma-assisted atomic layer deposition

“…By virtue of their unique material properties, nanostructures of III-nitride materials have been of considerable interest for various applications including piezotronic sensing, ambient energy harvesting, nanostructurebased lighting and computing devices, etc. [1][2][3][4][5][6][7][8][9][10][11][12][13] Numerous types of nitride nanostructures have been explored via either templateassisted or template-free fabrication methodologies. [14][15][16][17] In the template-assisted strategy, material growth is carried out on sacrificial nanostructured template materials such as carbon nanotubes, polymers, or anodic aluminum oxide (AAO).…”

Nanowire photodetectors based on wurtzite semiconductor heterostructures

“…The spectral response is dominated by the GaN sections of the nanowire, but the spectral contribution from the GaN wells, located in the 450-400 nm spectral range, can be resolved in photocurrent spectroscopy measurements performed at room temperature. The photoresponse drops significantly with decreasing temperature, which demonstrate that photogenerated carrier extraction is thermally assisted.Using a GaN/AlN (2.7 nm/ 5.3 nm) superlattice without GaN outer shell (seefigure 17), Lähnemann et al[89] showed a photocurrent that scaled sublinearly with the optical power. The spectral response clearly shows a sensitivity to wavelengths below 360−380 nm (cut-off associated to transitions to the first excited level in the quantum wells), and a rejection of longer wavelengths.…”