Study on vertical coupled quantum dots fabrication using selective area growth of nitride nano-pillars

宽带隙GaN和相关氮化物材料的量子点（QD）结构在用于诸如量子逻辑门的相干量子器件中具有很大的兴趣，因为在GaN/AlGaN界面处的2 eV的大导带偏移在其量子化能级中提供了强的电子约束。在直径为5 nm的GaN点中，基态和激发态之间的能量分离为125 meV。因此，我们可以用红外光源在量子点中强制振荡一个处于二进制量子态的电子。为了实现这种量子逻辑，使用GaN量子点的单电子晶体管是重要的，并研究了其制造工艺。采用分子束外延（MBE）选择性生长方法，在SiO2掩模的AlGaN衬底上生长GaN/AlN异质柱，在800 μ e的温度下形成垂直GaN量子点。直径为100 nm的GaN点的高度为5 nm，势垒厚度为1 nm。源电极和漏电极分别形成在衬底的背面和点的顶部。用于晶体管操作的栅电极在GaN生长工艺之前被掩埋在SiO2麝香中。在6 K下，观察到由于量子点中量子态的共振隧穿导致微分电导曲线的明显减小。电荷稳定性图显示在零源漏电压附近存在周期性的库仑金刚石结构。6 mV的充电能量对应于60 aF的自电容。通过将来将SiO2掩模直径减小到5 nm，将获得大的充电能量。这种GaN量子点形成技术和单电子器件是未来量子逻辑门的希望。

Quantum dot (QD) structures of wide bandgap GaN and related nitride materials are of great interest in use for coherent quantum devices such as quantum logic gate because the large conduction band offset of 2 eV at the GaN/AlGaN interface provides strong electron confinement in their quantized levels. The energy separation between ground and exited states in the GaN dot of 5nm in a diameter is large as 125 meV. So, we can forcibly oscillate an electron in binary quantum states in the quantum dot using infrared optical sources. In order to realize such quantum logic, single-electron transistor using GaN quantum dots is important and the fabrication process was investigated. The vertical GaN quantum dot was formed in a GaN/AlN heteropillar grown by MBE selective growth method on the SiO2 masked AlGaN substrate at 800Åe. The height of GaN dot with a 100 nm diameter was 5 nm and the barrier thickness was 1 nm. The source and drain electrodes were formed backside of the substrate and top of the dot, respectively. Gate electrodes for transistor operations were buried in SiO2 musk before GaN growth process. Clear reductions in the differential conductance curves due to resonant tunneling through the quantum states in the dot were observed at 6 K. The Charge stability diagram exhibited the periodically Coulomb diamond structures at near zero source-drain voltages regions. The 6 mV of the charging energy corresponds to self-capacitance of 60 aF. Large charging energy will be obtained by future decrease in SiO2 mask diameter to 5 nm. This GaN quantum dots formation technique and the single-electron devices are promising for future quantum logic gate.