ZnO Nanorods on Li-Doped ZnO Thin Films for Efficient p–n Homojunction Light-Emitting Diodes

Light-emitting diodes (LEDs) based on wide-band-gap ZnO have attracted widespread attention for use in solid-state lighting; however, their development has been hindered by the lack of a reliable, high-quality homojunction. In this work, an efficient p–n homojunction LED is fabricated based on the secondary growth of Ga-doped ZnO (GZO) nanorods onto a p-type Li-doped ZnO (LZO) thin film. Structural analyses reveal that both the GZO nanorods and LZO films possess a hexagonal structure with a c-axis orientation, and their crystalline quality is not affected by the incorporation of Ga or Li. The GZO nanorods with 4 atom % Ga and LZO films with 12 atom % Li show optimum optical and electrical properties. The homojunction fabricated from optimized GZO nanorods and LZO films exhibits the rectifying characteristics of a p–n junction LED with a low turn-on voltage of 3.2 V and a bright-yellow-orange electroluminescence (EL) band centered at 2.0 eV. Both the EL and electrical properties of the homojunction are found to be stable over a period of 2 months. The optimized LED based on the GZO nanorods is 16 times more efficient in EL than the equivalent device made from ZnO nanorods. The EL emission of the GZO/LZO homojunction can be explained by the formation of GaZn–VZn and LiZn deep-level defects induced by the incorporation of Ga and Li. These findings open opportunities to employ a doped ZnO homojunction as a highly efficient EL source in photonic devices.