Highly uniform ultraviolet-A quantum-confined AlGaN nanowire LEDs on metal/silicon with a TaN interlayer

Abstract

In this paper, we describe ultraviolet-A (UV-A) light-emitting diodes (LEDs) emitting at 325 nm based on a highly uniform structure of quantum-confined AlGaN quantum-disk nanowires (NWs). By incorporating a 20 nm TaN interlayer between a Ti preorienting layer and the silicon substrate, we eliminated the potential barrier for carrier injection and phonon transport, and inhibited the formation of interfacial silicide that led to device failure. Compared to previous reports on metal substrate, we achieved a 16 × reduction in root-mean-square (RMS) roughness, from 24 nm to 1.6 nm, for the samples with the Ti/TaN metal-bilayer, owing to the effective diffusion barrier characteristic of TaN. This was confirmed using energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). We achieved a considerable increase in the injection current density (up to 90 A/cm 2) compared to our previous studies, and an optical power of 1.9 μW for the 0.5 × 0.5 mm 2 NWs-LED. This work provides a feasible pathway for both a reliable and stable UV-A device operation at elevated current injection, and eventually towards low-cost production of UV devices, leveraging on the scalability of silicon substrates.

Diode junction temperature in ultraviolet AlGaN quantum-disks-in-nanowires

“…We have reported recently that AlGaN NWs grown on metal thin films can achieve higher injection current due to the increased electrical conductivity and the absence of the above-mentioned SiN x barrier at the substrate/NW interface. 20 We report a lower T j compared to planar UV GaN and AlGaN planar structures by using the same forward voltage method (compared to previous reports). Comparison of T j using the EL peak-shift method and infrared (IR) thermo-camera resulted in slightly lower values as previously reported in planar devices.…”

“…We recently demonstrated the growth of AlGaN NW LEDs on Ti/TaN/Si to circumvent the SiN x formation and substrate delamination. 20 We reported a higher injection current density due to the reduction of Si interdiffusion in the metal layer. This reduces the potential barrier at the semiconductor/substrate interface, increasing the injection efficiency and reducing Joule heating.…”

“…16 It has been recently demonstrated that the NW growth on metal thin films helps to avoid such issues, hence reducing the potential barrier for carrier flow and allowing increased current injections with lower Joule heating. [17][18][19][20][21] As many efforts have been made in the UV III-nitride NW community to bring NW technology to a practical application, it is of particular importance to study the diode T j of such devices to evaluate the best configuration for efficient heat dissipation through the heat sink substrate, prevent overheating, short lifespan, and reduced light intensity. To date, there are no reports on UV AlGaN (and in general IIInitride) NWs LED T j measurements; therefore, this work consists of experimental findings that aim to enlighten the UV LED NW community for designing and optimizing the diode structures and substrate and to realize high power and reliable devices for eventual practical implementation.…”

Quantified hole concentration in AlGaN nanowires for high-performance ultraviolet emitters

“…4(d). 28,42,[72][73][74][75] The device also shows good diode characteristics with a negligible leakage current, as depicted in the inset of Fig. 5(a).…”

Epitaxial Growth and Characterization of AlInN-Based Core-Shell Nanowire Light Emitting Diodes Operating in the Ultraviolet Spectrum

“…The AlInN LEDs have excellent current-voltage characteristic with low resistance measured at room temperature, shown in Figure 4(a). The leakage current was found to be very small which is about 1 µA at -8 V. Turn on voltage of these UV nanowire LEDs is ~ 5 V which is significantly lower compared to current thin-film AlGaN LEDs at similar wavelength range 44,45 and is also better/comparable to that of currently reported AlGaN UV nanowire LEDs 43,46,47 . Figure 4 This observation agrees well with the simulation results in which the TM polarized emission is more than two orders of magnitude strong than TE polarized light, shown in Figure 5(b).…”