Observation of 430 nm electroluminescence from ZnO/GaN heterojunction light-emitting diodes

Abstract

In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growing Ga-doped ZnO film of thickness 1 μm by chemical vapor deposition on the p-GaN layer. Room-temperature electroluminescence in the blue-violet region with peak wavelength 430 nm is observed from this structure under forward bias. Light–current characteristics of these light-emitting diodes are reported, and a superlinear behavior in the low current range with a slope 1.9 and a sublinear behavior with a slope 0.85 in the high current range are observed.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…The near-UV emission band centered at around 400 nm was attributed to the near-band-edge emission in ZnO nanowires originating from the recombination of ZnO free and bound excitons [377,380]. Whereas the redshifted violet emission band centered at about 430 nm was ascribed to the transitions from the conduction band or shallow donors to deep Mg acceptor levels in the p-GaN thin film substrate [372,377,380]. The blue emission at around 460 nm was assigned to the radiative interfacial recombination of the electrons from n-ZnO and holes from p-GaN [380][381][382].…”

“…The need for deposition of an ohmic electrode on the GaN substrate could be avoided by employing a ZnO nanowire/GaN substrate/ZnO nanowire heterostructure [370]. The turn-on voltage of the diode was about 3.5 V, which is relatively low, probably due to the presence of interfacial defects [372] owing to the low growth temperature (< 100 °C ) of the chemical method. Figure 44 shows an optical image (exposed for 9 s with a gain value of 1) of the lit-up LED at a forward bias voltage of 10 V. In the device, all of the nanowires were connected in parallel and each single nanowire is a light emitter.…”

“…There has also been a controversy about whether the emission is from the n-ZnO side [147,376] or the p-GaN side [372,377]. In reality, the hole concentration in the Mg doped p-GaN substrate (~10 18 cm -3…”

Zinc Oxide Nanophotonics

“…Due to the p-type doping problem, many researchers reported on the heterostructures with n-type ZnO grown on p-type materials of Si, GaN, and conducting oxides [27,54,140,141]. Among the possible heterostructures, the structure ZnO/GaN has attracted extensive interest [142][143][144] because device structures such as n-ZnO/pGaN can be readily realized because the lattice mismatch between ZnO and GaN is modest (1.9%) [145].…”

“…As-grown ZnO is highly n-type, so the main problem is to consistently produce p-doped ZnO, and it represents the main efforts of current research. As a result, most of the currently developed devices are based on heterojunctions [26][27][28]. Excellent properties of ZnO can be best employed by building heterojunctions with other p-type semiconductors.…”