| 초록 |
ZnO has been extensively studied for optoelectronic applications such as blue and ultraviolet (UV) light emitters and detectors, because it has a wide band gap (3.37 eV) and a large exciton binding energy of ~60 meV over GaN (~26 meV). However, the fabrication of the light emitting devices using ZnO homojunctions is suffered from the lack of reproducibility of the p-type ZnO with high hall concentration and mobility. Thus, the ZnO-based p-n heterojunction light emitting diode (LED) using p-Si and p-GaN would be expected to exhibit stable device performance compared to the homojunction LED. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducible availability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices with low defect density. However, the electroluminescence (EL) of the device using n-ZnO/p-GaN heterojunctions shows the blue and greenish emissions, which are attributed to the emission from the p-GaN and deep-level defects. In this work, the n-ZnO:Ga/i-ZnO/p-GaN:Mg (n-i-p) heterojunction LEDs were fabricated on c-plane sapphire substrates using RF magnetron sputtering method for the ZnO:Ga/ZnO and metal organic chemical vapor deposition for the GaN:Mg. The i-ZnO layers were grown with different growth times to realize true UV emission from the ZnO film. The I-V characteristic of the LEDs showed rectifying, diode-like behavior. The room-temperature EL was observed under forward bias. At forward bias, the spectra consisted of two peaks around 390 and 560 nm. The EL spectra revealed different emission intesity depending on the growth time of the i-ZnO layer. It is shown that the adequate thickness of the i-ZnO layer result in the advantage of acquiring high performance n-i-p LED devices. |
