變溫霍爾量測系統之建置與高電子遷移率通道之研究

Abstract

本論文主要談論利用致冷座與一可改變電流大小與方向性之電磁鐵電流源，建置一套可電腦控制之變溫霍爾量測系統，進行利用分子束磊晶成長之調變式摻雜法所得高電子遷移率之二維電子氣系統元件改變量測溫度之霍爾量測。並透過不同表面閘極偏壓以調變載子濃度，結合變溫量測來探討電子遷移率因為不同散射源之影響，摻雜源在元件中的深淺能階分佈情形，藉此找出影響電子遷移率的主要因素。然而在更換分子束磊晶系統的冷卻壓縮機真空幫浦中的逆止閥後，發現元件中背景雜質的降低帶來電子元件的突破。 然後利用較高電子遷移率之元件在低溫強磁的環境下進行二維電子氣系統的量子霍爾量測實驗，探討在變溫與變載子濃度下與量子霍爾效應的相對關係。 本文後段選擇在高換冷卻壓縮機真空幫浦逆止閥後所得到最高的電子遷移率元件上，利用電子束微影技術製作分離閘極之奈米結構，利用分離閘極的負偏壓夾止二維電子氣系統通道，得到電子一維通道的彈道傳輸後，進行一維彈道電子傳輸特性在變溫與變磁場環境下的研究。

In this work, we construct a temperature-dependent Hall measurement system which contains a cryostat and electromagnet with a current source changable in amplitude and direction to measure the modulation-doped high electron mobility sample grown by molecular beam epitaxy(MBE) . With changing the gate voltage ,we obtained dependence between sample mobility and concentration.By use of temperature-dependent and gate voltage-dependent Hall measurement ,we know that which scattering mechanisms dominate in sample mobility.In additional,we could also figure out the shallow and deep doping level in the sample.After replacing the O-ring of cyro-pump to gasket in MBE system,the sample mobility have been improved greatly. Under low temperature and high magnetic field, we measured quantum Hall effect of high mobility sample and found that the decreasing of ionized impurities in newly grown sample results in higher mobility. Finally, we fabricate split gate by electron-beam lithography in higher mobility sample and the split gate pinched off successfully.