Amplified spontaneous emission from ZnO in n-ZnO/ZnO nanodots-SiO2 composite/p-AlGaN heterojunction light-emitting diodes

This study demonstrates amplified spontaneous emission (ASE) of the ultraviolet (UV) electroluminescence (EL) from ZnO at λ∼380 nm in the n-ZnO/ZnO nanodots-SiO2 composite/p- Al0.12Ga0.88N heterojunction light-emitting diode. A SiO2 layer embedded with ZnO nanodots was prepared on the p-type Al0.12Ga0.88N using spin-on coating of SiO2 nanoparticles followed by atomic layer deposition (ALD) of ZnO. An n-type Al-doped ZnO layer was deposited upon the ZnO nanodots-SiO2 composite layer also by the ALD technique. High-resolution transmission electron microscopy (HRTEM) reveals that the ZnO nanodots embedded in the SiO2 matrix have diameters of 3-8 nm and the wurtzite crystal structure, which allows the transport of carriers through the thick ZnO nanodots-SiO2 composite layer. The high quality of the n-ZnO layer was manifested by the well crystallized lattice image in the HRTEM picture and the low-threshold optically pumped stimulated emission. The low refractive index of the ZnO nanodots-SiO2 composite layer results in the increase in the light extraction efficiency from n-ZnO and the internal optical feedback of UV EL into n-ZnO layer. Consequently, significant enhancement of the UV EL intensity and super-linear increase in the EL intensity, as well as the spectral narrowing, with injection current were observed owing to ASE in the n-ZnO layer.