An alternative to conventional gallium nitride (GaN)-based blue- and UV-emitting LED materials is found in zinc oxide (ZnO), which has a high direct bandgap energy, making it potentially useful in high-intensity LEDs for lighting. But ZnO can also emit longer wavelengths less efficiently through defect states. Scientists at National Taiwan University (Taipei, Taiwan) are combining ZnO with GaN along with ZnO doped with 0.5% gallium (GZO) to form LEDs that emit strongly at 377 nm through the more-desirable excitonic states.
For comparison, the group fabricated a GZO/ZnO/GaN diode with the ZnO sandwiched between two silicon dioxide (SiO2) barriers and a GZO/GaN diode with no SiO2 barriers. Both samples were fabricated on a GaN layer atop a sapphire substrate; the two layers of SiO2 in the sandwiched device were 2 and 5 nm. The researchers found that the nonsandwiched device emitted much more weakly and mostly through defect states (producing blue-green light). The difference occurs because the SiO2 barriers serve to confine carriers in the ZnO. If made practical, the UV-emitting LEDs would be combined with white phosphors for lighting. Contact JianJang Huang at [email protected].
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