Deep ultraviolet emitting polarization induced nanowire light emitting diodes with Al_xGa_1−xN active regions

Abstract

In this report, we demonstrate band gap tuning of the active region emission wavelength from 365 nm to 250 nm in light emitting diodes fashioned from catalyst-free III-nitride nanowires. Optical characteristics of the nanowire heterostructures and fabricated devices are studied via electroluminescence (EL) and photoluminescence spectroscopy over a wide range of active region compositions. It is observed that for typical nanowire plasma assisted molecular beam epitaxy growth conditions, tuning of emission to wavelengths shorter than 300 nm is hampered by the presence of an optically active defect level. We show that by increasing the AlGaN nanowire growth temperatures this defect emission can be suppressed. These findings are applied to growth of the active region of a nanowire light emitting diode, resulting in a polarization-induced nanowire light emitting diode with peak EL at 250 nm.

Tunnel junction enhanced nanowire ultraviolet light emitting diodes

“…UV emission spanning from GaN (365 nm) to AlN (210 nm) band gap wavelengths was demonstrated using AlGaN nanowires in the past few years [9]- [12]. A wavelength tunable polarization doped nanowire heterostructure has been used to demonstrate the first UVC nanowire LEDs [9]. The same heterostructure design was later used to study the free hole density in polarization graded AlGaN nanowires [13].…”

“…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).…”

“…Wavelength tunable multiple AlGaN quantum disks are inserted at the center of the nanowire separated by AlN barriers to serve as the active region. To make a p-type electrical contact at the bottom of the nanowires these doubly graded heterostructures are grown on p-type Si or high work function metals [9], [13], [15]. As shown in the energy band diagram ( Fig.…”

“…Furthermore, the efficiency droop in these nanowire LEDs is greatly reduced, which we attribute to enhanced non-equilibrium hole concentration due to interband tunneling. [16]- [18] is deposited followed by a doubly graded polarization doped UV LED structure as described earlier [9], [10], [13]. The nanowire heterostructures are grown from self-assembled catalyst free nanowires using a two-step [19]- [21] dynamic growth process byplasma assisted molecular beam epitaxy in a Veeco GEN 930 system.…”

“…The nanowire heterostructures are grown from self-assembled catalyst free nanowires using a two-step [19]- [21] dynamic growth process byplasma assisted molecular beam epitaxy in a Veeco GEN 930 system. The InGaN insertion in the TJ is grown at relatively low temperature (~600C) for effective In incorporation while the AlGaN active region is grown at relatively high temperature (~840C) to suppress optically active defects [9]. The AlGaN graded layers are doped with Mg (at the bottom) and with Si (at the top).…”