表面声波单电子输运器件中噪声特性探究

Acoustoelectric current driven by surface acoustic wave (SAW) offers a new approach towards the development of quantum current standard, which has aroused great scientific attention. Acoustoelectric current (AE) is easily affected by the surrounding environment, then displays random fluctuations owing to the noise, which limits the application of single electron devices in the measurement. Surface acoustic wave captures and handles the number of electrons, which depends on the superposition of piezoelectric potential of SAW and electrostatic potential of the channel..Employing the measured of I-Vds characteristics curve at fixed gate voltages, we can estimate the barrier height of a pinched-off quantum point contact (QPC). The devices fabricated with the different channel lengths and widths will be measured to obtain the barrier height in the quantized AE current plateaus region. And the relation among the quantized AE plateau width, quasi-one-dimensional channel length and gate voltage efficiency will be established. Furthermore, we can find how the potential distribution affect quantized AE plateaus..Combining theoretical modeling and detailed measurements of the current curves repeatedly swept under the same condition, current curves scanned with a small step, and the current curves versus time, we try to explore formation condition and physical origin of current fluctuations,and further analyze how to find the root of noise by means of technology and data analysis.All above provide support for improving device structure in future..Finally, we adjust the experimental parameters to reduce the AE current fluctuations, such as the SAW power, SAW frequency, source-drain bias, the gate voltage difference, and two counterpropagating SAW beams. In addition, designing the noise measurement circuit and wavelet denoising are applied in order to substantially improve the flatness of the quantized acoustoelectric current plateau.

表面声波单电子输运器件作为可能建立量子电流标准的一种途径，目前已成为各国物理学家关注的热点之一。表面声波搬运电子产生的声电电流易受周围环境影响，出现噪声，发生随机波动，影响单电子器件在计量方面的应用。本项目通过测量一系列不同结构器件的准一维通道势垒分布，得到表面声波单电子器件在量子化声电电流坪台处的势垒高度，并以此建立量子化声电电流坪台宽度、器件准一维通道长度和门电压效率三者之间的关系，从而发掘势垒分布对电流坪台的影响。本文旨在研究不同区域内声电电流波动和理论建模计算，探索其噪声形成条件及机制，并探讨如何从技术及数据分析上追溯其产生根源，为进一步改进器件结构提供技术支持，继而通过调节微波功率和频率、源漏偏压、门电压侧移等实验参数及引进两列波相向传输等实验手段调控声电电流波动，通过搭建测噪电路和小波变换去噪处理，进一步提高量子化声电电流坪台精度。

表面声波单电子输运器件作为可能建立量子电流标准的一种途径，目前已成为各国物理学家关注的热点之一。表面声波搬运电子产生的声电电流易受周围环境影响，出现噪声，发生随机波动，影响单电子器件在计量方面的应用。本项目通过测量一系列不同结构器件的准一维通道势垒分布，得到表面声波单电子器件在量子化声电电流坪台处的势垒高度，并以此建立量子化声电电流坪台宽度、器件准一维通道长度和门电压效率三者之间的关系，从而发掘势垒分布对电流坪台的影响。为了探索引起声电电流跳动的物理机理，我们从实验上详细研究了不同条件下声电电流的波动情况。研究主要从以下三个方面进行：（1）相同方向反复重扫；（2）不同区域小步进细扫；（3）固定测量参数扫描时间。根据测量结果，我们提出杂质的亚稳态（杂质得失电子状态）是引起声电电流波动的物理起源。通过调节微波功率，微波频率，源漏偏压和门电压侧移实验参数，并借助两列波对传和外加磁场的实验手段来抑制单电子器件中的电流跳动。测量结果表明：调节微波功率和频率通过改变移动量子点的深度很好地抑制了电流跳动；调节反向传输SAW 的相位可以改变驻波波腹和波节相对于准一维通道的位置，来改变移动量子点的形状，从而抑制了声电电流的跳动。