Department of Electrophysics, National Chiayi University , No. 300 Syuefu Road, Chiayi City 60004, Taiwan.
ACS Appl Mater Interfaces. 2017 Jul 19;9(28):23904-23908. doi: 10.1021/acsami.7b03201. Epub 2017 Jul 5.
MgZnO/ZnO two-dimensional electron gas (2DEG) structures with ZnO annealed at various temperatures (600-900 °C) and photodetectors (PDs) with and without a 2DEG structure were fabricated using a radio frequency magnetron sputtering system. It was found that the carrier concentration and mobility increase with the annealing temperature owing to the improved crystalline in ZnO; however, high-temperature (800 °C or higher) annealing can degrade the crystalline of the ZnO layer. Hall measurements showed that compared with that of bulk ZnO, the sheet carrier concentration of the 2DEG sample increased from 1.3 × 10 to 1.2 × 10 cm, and the mobility was enhanced from 5.1 to 17.5 cm/V s. This is because the channel layer is the total thickness (300 nm) in bulk ZnO, whereas the carriers are confined to a 45 nm region beneath the MgZO layer in the 2DEG sample, confirming the 2DEG behavior at the MgZnO/ZnO interface. The PDs with 2DEG structures demonstrate a higher ultraviolet (UV) response and a UV/visible rejection ratio that is six times larger than that of the PDs without a 2DEG structure. The 2DEG structure also induces a photocurrent gain, which results in a 240% quantum efficiency for the 310 nm incident wavelength. The related mechanism is elucidated with a band diagram.
采用射频磁控溅射系统制备了在不同温度（600-900°C）下退火的 MgZnO/ZnO 二维电子气（2DEG）结构和具有和不具有 2DEG 结构的光电探测器（PD）。研究发现，由于 ZnO 的结晶性提高，载流子浓度和迁移率随退火温度的升高而增加；然而，高温（800°C 或更高）退火会降低 ZnO 层的结晶性。霍尔测量表明，与体 ZnO 相比，2DEG 样品的薄片载流子浓度从 1.3×10 增加到 1.2×10 cm，迁移率从 5.1 提高到 17.5 cm/V s。这是因为通道层是体 ZnO 的总厚度（300nm），而在 2DEG 样品中，载流子被限制在 MgZO 层下方的 45nm 区域内，证实了 MgZnO/ZnO 界面处的 2DEG 行为。具有 2DEG 结构的 PD 表现出更高的紫外（UV）响应和 UV/可见光抑制比，是没有 2DEG 结构的 PD 的六倍。2DEG 结构还诱导出光电流增益，导致 310nm 入射波长的量子效率达到 240%。相关机制通过能带图进行了阐明。
