Excitonic electroluminescence from ZnO-based heterojunction light emitting diodes

Abstract

This work reports on the fabrication and characteristics of n-ZnO/p-GaN and n-ZnO/n-MgZnO/n-ZnO/p-GaN heterojunction light emitting diodes (LEDs). Both devices exhibited diode-like rectifying current-voltage characteristics. Room temperature electroluminescence (EL) spectra for both LEDs consisted of dominant emission at 375 nm and two weaker bands centred at 415 nm and 525 nm, which were attributed to ZnO excitonic transition and defect-related emissions from GaN and ZnO, respectively. Moreover, it was demonstrated that the single heterojunction required a higher injection current to obtain an excitonic EL than that for the n-ZnO/n-MgZnO/n-ZnO/p-GaN LEDs. This indicated that the insertion of the MgZnO layer confined the injection carriers and thus increased the intensity of excitonic emission in the ZnO active region.

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

“…6 Under reverse bias, large current has been observed. n-ZnO/p-GaN heterojunction devices without intrinsic or insulating layers frequently show leaky I-V curves 6,9,10,14,17,29 in agreement with large currents under reverse bias observed in our work. Large leakage current was previously attributed to Pool-Frenkel effect.…”

“…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. 21,28 These emissions have been attributed to different mechanisms in the literature.…”

Solution-based growth of ZnO nanorods for light-emitting devices: hydrothermal vs. electrodeposition

“…Large charge density at a GaN/ZnO interface is expected to result in a large band offset [40]. While small offsets of E c = 0.12 eV and E v = 0.15 eV based on Anderson model has been proposed [5,7,15], more comprehensive calculations predict significant band offsets, from 1.0 to 2.2 eV, with larger offsets in presence of interface charges [41]. Experimental findings also confirm relatively large band offsets, E v = 0.4-0.5 [42], and E v = 0.8 [43], and E c = 0.5-0.6 eV [42].…”

Ultraviolet Electroluminescence from ZnS@ZnO Core–Shell Nanowires/p-GaN Introduced by Exciton Localization

“…12,17,18 However, the intermediate layer has limited the carrier transportation and lead to the low light emitting efficiency. Due to the advanced physical and chemical properties, the integration of ZnO nanostructures (nanowires or quantum dots) with GaN could be a feasible approach to obtain light-emitting diodes (LEDs) with high performance.…”