(c) Schematic of a light emitting diode device. (d) The I-V characteristics of the heterojunction device. Figure 2 shows the PL spectra of the single ZnO microrod, p-GaN films, and ZnO/GaN heterostructure measured at room temperature. The PL spectrum of the ZnO microrod consists of an intense near-band-edge (NBE) UV emission centered at

380 nm attributed to the radiative recombination of free excitons and a broad green band due to the defect emission related to oxygen vacancies or zinc Selleck Ilomastat interstitials [25]. The p-GaN film exhibits the NBE-related UV emission peak at around 362 nm and the broad blue emission peak centered at 445 nm which can be attributed to transitions PD173074 datasheet from the conduction band or shallow donors to deep Mg acceptor levels [26]. The appearance of several oscillations is due to the

interference effects of the thickness of the smooth GaN film. The bottom line in Figure 2 shows the PL result of the ZnO/GaN heterostructure. The pumping laser beam can penetrate through the ZnO microrod into the underlying p-GaN. One additional emission peak centered around 490 nm could be obtained, which is attributed to the emissions arising from the carrier recombination in regions near the heterojunction interfaces [27]. The EL device can be operated at both forward and reverse bias current. The EL spectra of the heterojunctions under various forward biases are shown in Figure 3a. Under high forward bias current, there are two dominant emissions centered at 430 and 490 nm and a relatively weak emission of 380 nm at the short-wavelength shoulder of the first emission peak. see more The origin of the EL emission of heterojunction diodes can be confirmed by comparing the

EL with PL spectra. The emission around 430 nm is ascribed to the Mg acceptor levels in the p-GaN thin film. The blue emission around 490 nm comes from the ZnO MR/p-GaN interface; the electron would be captured by the deep-level states near the interface. The UV emission Bcl-w band around 380 nm is attributed to the excitonic emission in ZnO MR. Consequently, with the increase of the bias, a UV emission at 380 nm can be observed, but the EL spectra are still dominated by the blue emission. Figure 2 The room-temperature μ-PL spectra of single ZnO MR, p-GaN substrate, and ZnO/p-GaN heterojunction. Figure 3 The room temperature EL spectra of n-ZnO/p-GaN heterojunction LED (a) under various forward biases and (b) under reverse biases. The lighting images under the biases (+36 V and −30 V) are shown in the insets of (a) and (b), respectively. (c) The band diagram of the n-ZnO/p-GaN heterojunction devices under reverse bias. (d) The three light output intensities of the heterostructure as a function of injection current under reverse bias. More importantly, the excitonic emission of ZnO MR dramatically increases and becomes a distinct peak as the applied reversed biases increase as shown in Figure 3b.