For optoelectronic applications in the ultraviolet spectral range, besides GaN-based materials, ZnO and its alloys have attracted much attention in the last few years due to the possibility of using excitonic effects at room temperature in ZnO based materials. Recently, high quality ZnO has been grown with excellent properties. Bandgap engineering in ZnO can be accomplished using alloys with MgO because the ionic radius of Mg²⁺ (0.57Å) is close to that of Zn²⁺ (0.6Å). Mg_xZn_1-xO/ZnO alloy is considered to be a suitable potential barrier material. Although most of the previous works were focused on the fabrication of Mg_xZn_1-xO alloy thin films and of Mg_xZn_1-xO/ZnO QW, we found only few reports about PLD grown MgZnO/ZnO double heterostructure (DHS). Recently we reported on the demonstration of p-n junction LEDs fabricated from n-ZnO/p-GaN single heterostracture (SHS). In this study, we are going to investigate the structural, optical and electrical properties of n-Mg_xZn_1-xO/ZnO/p-GaN double heterostructure (DHS) grown by pulsed laser deposition. DHS design is expected to improve optical and thermal characteristics of LEDs with ZnO-based active regions.

The Mg_xZn_1-xO/ZnO films were deposited by PLD using a KrF excimer laser operating at 248 nm, on p-GaN/sapphire substrate. The growth temperature is 600 ^oC. The structures of ZnO films were studied by an X-ray diffractometer and the surface morphologies of the thin films were investigated by a scanning prove microscope in the AFM mode. Also, the photoluminescence (PL) was measured under excitation with He-Cd laser operation at 325 nm. The enhancement of the Mg incorporation at high temperature is due to the stronger bonding strength of Mg-O than that of Zn-O, which induced a blueshift of the PL emission. In addition, the deposition at high temperature enhanced the UV peak intensity and the intensity ratio of UV/deep-level emission.   

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