Nanoscale Electronic Conditioning for Improvement of Nanowire Light-Emitting-Diode Efficiency

Abstract

Commercial III-Nitride LEDs and lasers spanning visible and ultraviolet wavelengths are based on epitaxial films. Alternatively, nanowire-based III-Nitride optoelectronics offer the advantage of strain compliance and high crystalline quality growth on a variety of inexpensive substrates. However, nanowire LEDs exhibit an inherent property distribution, resulting in uneven current spreading through macroscopic devices that consist of millions of individual nanowire diodes connected in parallel. Despite being electrically connected, only a small fraction of nanowires, sometimes <1%, contribute to the electroluminescence (EL). Here, we show that a population of electrical shorts exists in the devices, consisting of a subset of low-resistance nanowires that pass a large portion of the total current in the ensemble devices. Burn-in electronic conditioning is performed by applying a short-term overload voltage; the nanoshorts experience very high current density, sufficient to render them open circuits, thereby forcing a new current path through more nanowire LEDs in an ensemble device. Current-voltage measurements of individual nanowires are acquired using conductive atomic force microscopy to observe the removal of nanoshorts using burn-in. In macroscopic devices, this results in a 33× increase in peak EL and reduced leakage current. Burn-in conditioning of nanowire ensembles therefore provides a straightforward method to mitigate nonuniformities inherent to nanowire devices.

Enhanced electro-optic performance of surface-treated nanowires: origin and mechanism of nanoscale current injection for reliable ultraviolet light-emitting diodes

“…1(b)) that allow better metal-semiconductor contact and current injection, as well as the removal of surface states at the nanowires sidewalls. It is worth mentioning that some electrical shorts exist in the sample, hence carrying most of the current injected [28]. However, the I-V characteristics of such nanowires have been removed for a more representative comparison.…”

“…Conductive atomic force microscopy (c-AFM) has been previously utilized to study the nanoscale behavior of single nanowires and to visualize the electrical inhomogeneity [25][26][27][28][29]. This powerful technique allows a systematic investigation of rapid electrical properties without directly fabricating the device, hence enabling an immediate feedback on the grown sample quality.…”

Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

“…The same group further analyzed the current spreading on NWs-LEDs and the mechanism that reduces the electroluminescence emission also by employing cAFM. 168 Due to the presence of electrical shorts (low-resistance NWs) where most of the current passes through, uniform current distribution was not possible. Taking this into account, the ensemble NWs-LED were intentionally overloaded with relatively high voltage to render them as open circuit paths, thereby allowing uniform distribution of current across the whole device.…”

Compositionally Graded AlGaN Nanostructures: Strain Distribution and X-ray Diffraction Reciprocal Space Mapping

“…Semiconductor nanostructures have made a deep impact on studying the fundamental properties of materials and nowadays are explored as alternative components for nanodevice fabrication. The high surface-to-volume ratio of nanostructures makes their properties very sensitive to device design, i.e., quantum discs­(well)-in-nanowires (NWs), core–shell nanostructures, axial heterostructure NWs, compositional graded NWs, − etc. The misfit strain in such nanostructures can relax elastically toward the free surfaces (facets), even for large lattice-mismatched materials.…”