Electroluminescence at 375nm from a ZnO∕GaN:Mg∕c-Al2O3 heterojunction light emitting diode

Abstract

n - Zn O ∕ p - Ga N : Mg heterojunction light emitting diode (LED) mesas were fabricated on c-Al2O3 substrates using pulsed laser deposition for the ZnO and metal organic chemical vapor deposition for the GaN:Mg. High crystal quality and good surface morphology were confirmed by x-ray diffraction and scanning electron microscopy. Room temperature (RT) photoluminescence (PL) showed an intense main peak at 375nm and a negligibly low green emission indicative of a near band edge excitonic emission from a ZnO layer with low dislocation/defect density. The LEDs showed I-V characteristics confirming a rectifying diode behavior and a RT electroluminescence (EL) peaked at about 375nm. A good correlation between the wavelength maxima for the EL and PL suggests that recombination occurs in the ZnO layer and that it may be excitonic in origin. This also indicates that there is significant hole injection from the GaN:Mg into the ZnO.

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

“…For both SOG and PMMA devices, achieved efficiencies are much higher compared to previous reports on heterojunction LEDs based on n-ZnO/p-GaN. 6,29 While the nitride based devices which are currently commercially available can exhibit higher brightness and efficiency compared to the devices in this work, it should be noted that we do not use any kind of reactive ion etching which simplifies device fabrication. Also, the light extraction from the devices and the contact resistance is currently not optimized, so that further improvements can be expected with device optimization.…”

“…42 At higher forward bias (4.5 V < V < 15 V), the I-V curve could be described with I $ V b , where b ¼ 2.1, close to the I $ V 2 relationship common for wide band gap materials. 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.…”

“…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.…”

“…The reported efficiency of the devices was typically very low, 6 below 0.1%. 6,29 The brightness that we have obtained from a simple p-GaN/n-ZnO heterojunction (P1) is of the order of tens of cd/m 2 . On the other hand, devices on QW1 and QW2 exhibited significantly brighter emission under reverse bias.…”

“…In those few cases, where efficiency was given, it was typically low (0.00005% (Ref. 6) and 0.06% (Ref. 29)).…”