Sub-milliwatt AlGaN nanowire tunnel junction deep ultraviolet light emitting diodes on silicon operating at 242 nm

Abstract

We report AlGaN nanowire light emitting diodes (LEDs) operating in the ultraviolet-C band. The LED structures are grown by molecular beam epitaxy on Si substrate. It is found that with the use of the n+-GaN/Al/p+-AlGaN tunnel junction (TJ), the device resistance is reduced by one order of magnitude, and the light output power is increased by two orders of magnitude, compared to AlGaN nanowire LEDs without TJ. For unpackaged TJ ultraviolet LEDs emitting at 242 nm, a maximum output power of 0.37 mW is measured, with a peak external quantum efficiency up to 0.012%.

AlGaN Nanowires for Ultraviolet Light-Emitting: Recent Progress, Challenges, and Prospects

“…The typical device size varies from 300 µm × 300 µm to 1 mm × 1 mm. Comparing the light emission intensity under optical pumping and electrical injection for device structures with and without the tunnel junction, a drastic improvement of light intensity under electrical injection (by more than two orders of magnitude) is measured, whereas a similar intensity is measured under optical pumping; this indicates that the improvement of light intensity under electrical injection is due to the improved carrier injection (i.e., the injection of charge carriers into the active region) [37]. It is noted, though, tunnel junctions involving large bandgap thin films have remained challenging to realize.…”

“…Further, given the low cost of Si substrate, the majority of studies of group-III nitride nanowire UV LEDs are on Si substrate. These nanowire LED structures are primarily grown by MBE (through a spontaneous formation process, as afore-discussed), and predominantly with AlGaN ternary nanowires [25,36,37,51,[65][66][67][68][69]. The relatively longer history of investigating the MBE growth of AlGaN nanowires on Si, compared with the growth on other foreign substrates, has also made AlGaN nanowire UV LEDs on Si of better performance compared with devices on other foreign substrates, albeit with various limitations of using Si substrate (see Section 4).…”

“…It is seen that a relatively uniform nanowire height and top-surface diameter can be achieved even if the nanowires are spontaneously formed. The device fabrication process involves photolithography and metallization [36,37]. The typical device size varies from 300 µm × 300 µm to 1 mm × 1 mm.…”

Tunnel-injected sub-260 nm ultraviolet light emitting diodes

“…1 Research efforts over the past decade have led to the demonstration of UV light emission over a wide wavelength range from 400 nm to 210 nm. [2][3][4][5] Considerable improvements in substrate and active region quality have been achieved by optimizing the growth techniques, resulting in high radiative efficiency (~ 80%). 2 However, current UV LEDs exhibit significantly lower wall-plug efficiency as compared to their blue LED counterparts.…”

Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy

“…This electrical performance is drastically improved compared to the previously reported planar AlN LEDs [39], which is attributed to the significantly enhanced Mg-dopant incorporation in nanowire structures and the resultant efficient p-type conduction, as discussed previously. Recently, AlGaN ternary nanowire deep UV LEDs with excellent electrical performance have also been demonstrated [42,[89][90][91]. There are two important factors that contribute to such unusually high free hole concentration/efficient p-type conduction in the ultra-wide-bandgap AlN:…”