Multistage ballistic rectifiers on Si/SiGe hetreostructures

在调制掺杂Si/SiGe异质结构上制备了多级弹道整流器。它们的单级由不对称的纳米级交叉结组成，表现出抛物线的输出电压与输入电流特性。因此，输出电压的极性与输入电流的极性无关。这种全波整流的机制依赖于在动量弛豫长度（MRL）的距离上的无电流电压通道的静止充电，如果MRL大于交叉结的横向尺寸。由于单级的输出电压仅达到几mV，因此技术应用需要许多整流级。在本项目中，我们利用最近发表的效果，输入电流的增加，如果出现的阶段分离小于MRL，并在双级整流器的输出电压的一个因素，由于抛物线传输特性的协同增益。因此，整流器级尽可能靠近地定位。首先，在低温下通过非线性输运状态下的测量来确定单级的整流器效率。如从研究密集定位的双级弹道整流器所假设的，单个整流器级的效率由于限定不对称交叉结的潜在景观的相互干扰而恶化。这个问题将尽可能通过改进的几何形状来解决。在4 ~ 120 K的温度范围内，研究了优化的多级整流器的电流附加效应。最后，将确定实现接近输入电压的输出电压所需的级数。适当制备的多级整流器将根据与其作为技术装置使用相关的参数进行表征。

Multistage ballistic rectifiers are prepared on modulation-doped Si/SiGe heterostructures. Their single stages consist of asymmetric nanoscale cross junctions, which exhibit a parabolic output-voltage-vs-input-current characteristic. Accordingly, the polarity of the output voltage is independent of that of the input current. The mechanism of this full-wave rectification relies upon a stationary charging of the current-free voltage channel over the distance of the momentum relaxation length (MRL), if the MRL is larger than the lateral dimension of the cross junction. Since the output voltage of a single stage only reaches a few mV, many rectifier stages are necessary for technical applications. In the present project, we exploit the recently published effect of input-current addition, which arises if the stage separation is smaller than the MRL, and which in dual-stage rectifiers causes a synergy gain in the output voltage of a factor of two due to the parabolic transfer characteristic. Therefore, the rectifier stages are positioned as close as possible. At first, the rectifier efficiency of the single stages is determined at low temperatures by measurements in the nonlinear transport regime. As assumed from studying densely positioned dual-stage ballistic rectifiers, the efficiency of the single rectifier stages is worsened by mutual disturbing of the potential landscape defining the asymmetric cross junctions. This problem is to be solved as far as possible by an improved geometry. Accordingly optimized multiple-stage rectifiers are studied regarding their current-addition effects in a temperature range from 4 K to 120 K. Finally, the number of stages will be determined which is necessary to achieve an output voltage approaching the input voltage. Appropriately prepared multi-stage rectifiers will be characterised with respect to parameters which are relevant for their use as technical device.