Li-N Codoping Of P-type ZnO Based Films And Their Applications In Optoelectronic Devices

Zinc oxide (ZnO) has a direct wide bandgap (3.37 eV) and a large exciton binding energy (60 meV). It is a promising candidate for high-performance ultraviolet light-emitting devices (LEDs) and low threshold laser diodes. However, the reported performance of ZnO homojunction LEDs is still far below expectation. The main factor that limits the performance of ZnO homojunction LEDs lies on its poor p-type conduction of ZnO. The present work is focused on the subject of how to improve the performance of ZnO-based LEDs and random lasers. The following results have been achieved:1. Enhanced emission from ZnO-based LEDs by a distributed Bragg reflector: Double hetero-structured n-MgZnO/i-ZnO/p-MgZnO LEDs have been fabricated and the p-type MgZnO layer was obtained via a lithium-nitrogen codoping method. Obvious emission at around 400 nm has been observed from the LEDs under forward bias. To increase the light extraction from the LEDs, a distributed Bragg reflector whose reflectivity is 98% at 400 nm was bonded on the back side of the device, and the emission of the device was enhanced by around 1.6 times with the reflector.2, Improved performance of ZnO-based LEDs by introducing a hole-injection layer:By introducing a p-type GaN as the hole-injection layer, n-ZnO/p-ZnO/p-GaN LEDs have been fabricated. The output power of the LEDs can reach 18.5μW when the drive current is 60 mA, which is almost three orders of magnitude larger than the pristine LEDs without the hole-injection layer. The improved performance can be attributed to the extra holes injected into the p-ZnO layer from the p-GaN hole-injection layer.3. Electrically pumped random lasing realized in ZnO-based p-n junctions with high crystalline ZnO nanowire arrays as the active layer:Well-aligned ZnO nanowire arrays have been prepared by MOCVD technique, and p-MgZnO has been deposited by MBE technique onto the nanowires to form ZnO nanowires/ p-MgZnO core-shell heterostructures. Under the injection of continuous current, random lasing with a threshold current of around 15 mA has been observed from the heterostructures. The low threshold may be due to the relatively high crystalline quality of the ZnO nanowires as well as the effective carrier confinement in the heterostructures. These results suggest that nanowire core-shell p-n heterostructures may be a promising structure for electrically pumped random lasers. The performance of the laser diode has been improved by using a p-type diamond as a hole injection layer to increase the hole injecting into the nanowires.