鄰近環境對介觀量子通道電性質的影響

Abstract

本論文探討由分離閘極侷域的類一維窄通道在低溫時電性傳輸受其鄰近環境的影響。我們利用微影技術在具有高遷移率的二維電子氣的GaAs/AlGaAs異質結構樣品上製作六支相鄰的獨立金屬閘極，透過施加負偏壓於金屬閘極同時獨立控制窄通道寬度及其附近的位能阱，亦可改變樣品的溫度，觀察這些鄰近環境因子對其電性質的影響。 我們首先確認單一窄通道的品質，在閘極偏壓對窄通道電導的關係量測中觀察到量子化電導，在源極-汲極能譜圖中可觀察到明顯的次能帶結構以及零偏壓異常峰值，兩者皆隨著溫度、雜質分布和窄通道幾何形狀的不同而變化，其中零偏壓異常峰值觀察到隨溫度升高而消失。 對一固定寬度的窄通道，改變鄰近其它閘極的偏壓，推測雜質電荷累積造成的散射點使得窄通道的電導值展現額外一微小峰值，以及，在費米能量附近兩相鄰窄通道內的次能帶錯位時，會產生一反射電子與原先流經固定通道寬度的窄通道的電子相干涉，造成了固定通道寬度的窄通道電導曲線的震盪行為。

We have studied the effect of local environment on the electrical properties of gate confined quasi-one-dimensional channels at low temperature. By lithographic technique, six isolated nearby metal gates were fabricated on high mobility GaAs/AlGaAs heterostructure. The channel width and nearby potential profiles can be varied by individually biasing these metal gates. The temperature of the sample is also easily controlled. This work focused on the response of the electrical properties of the channel to local environmental factors. The observation of quantized conductance secures the quality of each narrow channel. The source-drain spectroscopy demonstrates subband structure and zero bias anomaly notably. Both source-drain spectroscopy and zero bias anomaly are sensitive to temperature, impurities and the shape of narrow channels. The zero bias anomaly peak decreases with increasing temperature. For a channel of a fixed width, a very small conductance peak appears upon varying nearby gates’ voltage ascribing to additional scattering points which arise from accumulated charges of impurities. In the other split gate configuration, we find that electrons would be backscattered due to misaligning subband bottoms of two adjacent quasi-one dimensional channels. The backscattered electrons would interfere with the original current leading to the conductance oscillations by continuously changing the energy levels of the adjacent narrow channel.