Separate Evaluation of Electron Coherence Influence Factors in Quantum Device by Resonant Tunneling Structures

本研究的目的是阐明利用谐振隧道二极管（RTD）的IV特性分别评价电子相干性影响因素（相弛豫、结构不均匀性和温度）的可能性。提出了一种利用RTD的IV特性评价电子相干性的方法。该方法将IV曲线分为三个区域，即a)电流截止区，b)电流上升区，c)电流峰值区。通过完全拟合实验测量的IV曲线，可以分别从a)区和b)区评价电子相相干性和结构不均匀性。为了验证该方法的有效性，我们对采用阶梯流动模式生长的InP/InGaAs RTD进行了评价。假设井宽波动为0.6 nm，在4.2K下测量的IV数据在电流量级上从a)到c)完全拟合，我们证实了我们提出的方法的有效性。接下来，我们模拟了杂质在发射极和集电极中的随机分布对IV特性的影响。然后，我们发现对a)区域的影响很小的情况。例如，当掺杂密度为3x10^<17>cm^<-3>时，使用长度为2.6nm的间隔层可以抑制这种影响。最后，利用已有的理论方法，我们成功地给出了一个可以单独评价电子相干性的RTD结构。

The objective of the research is to clarify a possibility to separately evaluate electron coherence influence factors, that is, phase relaxation, structural inhomogeneity, and temperature, by using IV characteristics of resonant tunneling diode(RTD).We proposed an evaluation method of electron coherence by IV characteristics of RTD. In the method, IV curves are divided into three regions, that is, a)current cut-off region, b)current raising region, and c)current peak region. By fitting experimentally measured IV curve completely, electron phase coherence and structural inhomogeneity can be evaluated from region a)and b)respectively.To confirm effectiveness of present method, we evaluated a InP/InGaAs RTD which was grown by the step flow mode. IV data measured at 4.2K was completely fitted over three orders in current magnitude from region a)to c)by assuming well width fluctuation of 0.6 nm, and we confirmed the effectiveness of our proposed method.Next, we modeled the influence of random distribution of impurities in the emitter and collector electrodes on IV characteristics. Then, we found the condition that the influence on the a)region was quite small. For example, the influence was suppressed with a spacer layer of length 2.6nm when a doping density was 3x10^<17>cm^<-3>.Finally, by using the theoretical method obtained thus far, we succeeded to give a RTD structure where the electron coherence could be evaluated separately.