Forward- and reverse-biased electroluminescence behavior of chemically fabricated ZnO nanotubes/GaN interface

Abstract

Electroluminescence characteristics of an n-ZnO nanotubes/p-GaN heterostructure light-emitting diode (LED) have been investigated at forward and reverse bias. Distinctly different emission spectra have been observed and the location of the recombination of electron-hole is analyzed under both configurations. The forward-biased emission spectrum shows two peaks centered at around 450 and 560 nm, while the reverse-biased spectrum exhibits a single emission peak at 650 nm. By comparing the current transport mechanisms, it is suggested that the violet-blue emission peak (450 nm) observed only under forward bias is originating from the heterojunction of the ZnO nanotubes/p-GaN LED. The influence on the emission intensity of the device with the increase in temperature at constant current is studied in the range from 25 to 65 • C, to check its compatibility for practical applications and under harsh conditions.

ZnO nanorod/GaN light-emitting diodes: The origin of yellow and violet emission bands under reverse and forward bias

“…The origin of the emission peaks is discussed in more detail in Subsection III D. There are two possible mechanisms to explain emission under reverse bias, reverse breakdown, 9 and tunneling across the interface. 4,8,10,12,13, 28 The presence of a UV emission peak at $365 nm corresponding to the band gap energy of GaN ($365 nm) which occurred at higher reverse bias voltages (>12.5 V) was attributed to avalanche breakdown due to strong electric field. 9 In some of the devices, blue emission from p-GaN can also be observed, and it decreases with increasing bias voltage while UV emission increases.…”

“…The tunneling is expected to occur due to the large energy band offset at p-GaN/n-ZnO interface. 4,8,10,12,13,28,[45][46][47] The yellow (or orange yellow) emission appears at relatively low bias voltages, so that it likely occurs due to tunneling. Tunneling phenomena in III-nitride heterojunctions have been previously observed for different material combinations.…”

“…Concerning the difference in peak position between yellow and orange-red emission, this has been attributed to the transition involving deep acceptors (yellow) and transitions involving deep donors and deep acceptors (red). 28 For different materials in contact with p-GaN and for various p-GaN structures, changes in the energy level alignment across the interface would be expected, which would affect contributions of individual defect levels to the emission spectrum.…”

“…23 However, very different behavior has been reported for pGaN/n-ZnO devices even for similar device architectures, which makes it difficult to establish strategies for the improvement of device performance. For example, in addition to devices lighting up under forward bias, devices lighting up under reverse bias 4, [8][9][10]12,13,28 have been reported. Also, a variety of the emission peaks at different wavelengths have been observed, including UV, UV-violet, violet-blue, green, yellow, and orange-red, with multiple peaks frequently present 11,14,18,19,22 which in some cases results in white emission.…”

“…Also, a variety of the emission peaks at different wavelengths have been observed, including UV, UV-violet, violet-blue, green, yellow, and orange-red, with multiple peaks frequently present 11,14,18,19,22 which in some cases results in white emission. 21,28 These emissions have been attributed to different mechanisms in the literature. The assignment of the emission peaks in the electroluminescence (EL) spectra is typically performed on the basis of comparison with the photoluminescence (PL) spectra.…”