Polarization-Induced pn Diodes in Wide-Band-Gap Nanowires with Ultraviolet Electroluminescence

Abstract

Almost all electronic devices utilize a pn junction formed by random doping of donor and acceptor impurity atoms. We developed a fundamentally new type of pn junction not formed by impurity-doping, but rather by grading the composition of a semiconductor nanowire resulting in alternating p and n conducting regions due to polarization charge. By linearly grading AlGaN nanowires from 0% to 100% and back to 0% Al, we show the formation of a polarization-induced pn junction even in the absence of any impurity doping. Since electrons and holes are injected from AlN barriers into quantum disk active regions, graded nanowires allow deep ultraviolet LEDs across the AlGaN band-gap range with electroluminescence observed from 3.4 to 5 eV. Polarization-induced p-type conductivity in nanowires is shown to be possible even without supplemental acceptor doping, demonstrating the advantage of polarization engineering in nanowires compared with planar films and providing a strategy for improving conductivity in wide-band-gap semiconductors. As polarization charge is uniform within each unit cell, polarization-induced conductivity without impurity doping provides a solution to the problem of conductivity uniformity in nanowires and nanoelectronics and opens a new field of polarization engineering in nanostructures that may be applied to other polar semiconductors.

Tunnel junction enhanced nanowire ultraviolet light emitting diodes

“…Fig. 1 shows the schematic diagram of a wavelength tunable polarization doped nanowire UV LED structure [9], [10], [13]. Catalyst free GaN nanowires exhibit a dominant N-face polarity [14] which induces p-type (n-type) conductivity at the base (top) of the nanowire when compositionally graded from GaN to AlN (AlN to GaN).…”

Progress and Prospects in Stretchable Electroluminescent Devices

“…One-dimensional inorganic nanostructures have been intensively studied recently with the interesting proper- ties of increased charge injection efficiency at the nanosize junctions and increased light-extraction efficiency in the wave-guide structures [24][25][26][27][28][29][30][31]. Compared to the thinfilm ILEDs, the inorganic nanowire (NW) structures possess inherent advantages for "soft" LEDs with its onedimensional configuration.…”

Structure-Properties Relations in III-Nitride Nanostructures for Optoelectronics

“…In particular, single crystal III-N nanowires can be grown on a variety of substrates while retaining their high optical and electronic quality. Here we discuss a few illustrative examples of correlating the atomic scale structure determined by scanning transmission electron microscopy (STEM) measurements with the functional properties of the nanowire heterostructures.Previously, we developed polarization-induced nanowire pn-junctions that take advantage of the built-in polarization dipole of the III-Nitride semiconductors [1]. To form these nanowire LEDs, p-GaN (Mgdoped) nanowires are first nucleated on Si (111) substrates using plasma-assisted molecular beam epitxay (MBE).…”