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

Abstract

Self-assembled nanowires are posed to be viable alternatives to conventional planar structures, including the nitride epitaxy for optoelectronic, electronic and nano-energy applications. In many cases, current injection and extraction at the nanoscopic scale are essential for marked improvement at the macroscopic scale. In this investigation, we study the mechanism of nanoscale current injection and the origin of improvement of the flow of charged carriers at the group-III nitride semiconductor surface and metal-semiconductor interfaces. Conductive atomic force microscopy (c-AFM) and Kelvin probe force microscopy (KPFM) enable a rapid analysis of the electrical and morphological properties of single and ensemble nanostructures. The surface potential and current injection of AlGaN nanowirebased LEDs are spatially mapped before and after surface treatment with KOH solution. Treated-nanowires showed an improved current spreading and increased current injection by nearly 10×, reduced sub-turn-on voltage (as low as 5 V), and smaller series resistance. The reduced contact potential confirms the lower semiconductor/metal barrier, thus enabling larger carriers flow, and correlates with the 15% increase in injection efficiency in macroscopic LEDs. The improvement leads to the normalization of nanoscale electrical conducting properties of UV AlGaN-based nanowire-LEDs and lays the foundation for the realization of practical nanowire-based device applications.

Functional integrity and stable high-temperature operation of planarized ultraviolet-A AlxGa1−xN/AlyGa1−yN multiple-quantum-disk nanowire LEDs with charge-conduction promoting interlayer

“…[25][26][27] The wide depletion layer region caused by Fermi level pinning results in a reduction in the free electron density near the semiconductor nanowire surfaces, thereby increasing the non-radiative recombination in the active regions and adversely affecting its quantum efficiency. 3,28 As confirmation, we observed a maximum J value of about 100 A/cm 2 at V F = 11 V at room temperature from the J-V F measurements on the parylene-free LED sample (compared to 140 A/cm 2 in the planarized sample, as reported earlier). Parylene-C is known to significantly suppress UV emission below 280 nm.…”

“…In recent years, the heterogeneous integration of a variety of inorganic materials for fabricating electronic and optoelectronic devices on sapphire 1, 2 and silicon (Si) [3][4][5][6][7][8] has shown clear promise in reshaping the future of the electronics industry. Additionally, the high thermal and chemical stability of the group III-nitride material system indicates its potential application in harsh environments in comparison to conventional silicon-based optoelectronic devices, which have limited operating temperature range and require extra protective packaging.…”

“…a) shows the extracted ideality factor values, which were derived from the slopes of the semilogarithmic J-V F curves at low V F values, whereasFigure 5(b) depicts the extracted series resistance (R s ) values, which were extracted using linear fits of the linear-scale curves at high injection current levels 3. The ideal p-n junction diode equation is 23 (a) Semilogarithmic scale χEL for parylene-free AlxGa1−xN/AlyGa1−yN nanowire-based UV-A LED at various temperatures.…”

Anisotropic Piezoelectric Response from InGaN Nanowires with Spatially Modulated Composition and Topography over a Textured Si(100) Substrate

“…Most notably, the current signal vacancy area moves to the left pyramid facet, which in turn proves that the electrical response almost disappears at the descending pyramid facet with respect to the scan direction. Obviously, the effective nanocontact between the NWs and probe tips for either electrical conduction or deformation interaction has a strong correlation with their relative geometry under both motional and static conditions. , For better illustration, the 2D height and current distribution images are also presented in Figure S4.…”

Deep-ultraviolet integrated photonic and optoelectronic devices: A prospect of the hybridization of group III–nitrides, III–oxides, and two-dimensional materials

“…By growing quasi-one-dimensional (quasi-1D) group III-nitride nanostructures using plasma-assisted molecular beam epitaxy (PA-MBE) [30,138,[213][214][215][216] , dislocation-and piezoelectric polarization-free Al x Ga 1−x N-based light-emitting nanowire structures can be realized. Nanowires have the advantage of allowing for the growth of lattice-mismatched foreign substrates, such as silicon and sapphire [217][218][219][220][221] , in addition to achieving nearly defect-free crystals [222,223] , and therefore, opportunity for fabricating high efficiency optoelectronic devices, including LEDs and lasers, because of the highly effective lateral stress relaxation associated with the nanowire large surface-area-to-volume ratios [224][225][226][227][228] . However, because of the higher surface-area-to-volume ratios in lower-dimen sional semiconductor structures and the subsequent formation of deep-level surface trap energy states, the intrinsic properties of d-dimensional semiconductor structures for all d {0,1,2} are directly influenced by their surface condition [229][230][231][232][233][234] .…”