二維銅/鍺多層膜傳輸特性之研究

Abstract

我們以熱蒸鍍的方法製作了一系列銅/鍺（Cu/Ge）多層膜樣品，再將部分樣品以爐管加熱，比較樣品加熱前與加熱後電阻（電導）隨溫度變化的關係，與在低溫下樣品磁電阻的變化。樣品銅單層的厚度約在30Å∼1600Å之間，不過電阻和磁電阻的量測與分析，以銅單層厚度在200Å以下的樣品為主，而鍺單層的厚度約在60Å∼115Å之間，大部分樣品鍺單的層厚度約為100Å。而將樣品放入爐管加熱的溫度分別為150oC、235oC、400oC。 在電阻量測方面，低溫下大部分的樣品（銅單層厚度小於230Å）電導的變化率對溫度的自然對數成線性關係，表示樣品的傳輸維度為二維，隨著銅單層厚度的減少，樣品的方塊電阻值上升，電導變化的斜率越大，樣品的無序程度越大。而樣品經過加熱之後，方塊電阻值下降了，且變化的電導與溫度的自然對數關係的斜率變小，表示樣品經過加熱後無序程度變小了。 在磁電阻量測方面，量測的溫度在0.3K∼13K，磁場範圍在0T∼1T，將所量測到的磁電阻以弱局域理論擬合，以求得自旋-軌道散射時間τso與非彈性散射時間τin。樣品的τso約為0.5ps左右，接近一定值，而樣品的非彈性散射時間則隨著銅單層厚度的減少而下降（非彈性散射率上升）。非彈性散射率亦與溫度的變化有關，隨著溫度的上升而上升，其與溫度關係可寫成（1/τin α T^P），利用非線性擬合可得到樣品的P值介於2∼3之間。P值隨著電導變化相對ln(T)的斜率上升而下降，而隨著擴散係數的下降P值下降，也就是說，在較接近clean limit時P值為3，隨著無序程度增加P值漸減而接近於2。

We have made a series of Cu/Ge multilayers samples with different individual layer thicknesses 30Å≦tCu≦1600Å and 60Å≦tGe≦115Å for Cu and Ge, respectively. All samples were made by thermal evaporation, and some of them were annealed at 150oC, 235 oC and 400 oC. The measurements and analyses of the resistance and the magnetoresistance are mainly on the samples with tCu≦200Å and tGe≡100Å . The samples with tCu≦230Å show 2-D transport properties inferred from their linear relations between sheet conductance and logarithm of temperature at low temperatures. As tCu is reduced, the sheet resistance of sample goes up as well as the slope of sheet conductance respect to logarithm of temperature. After being annealed, samples show both sheet resistance and the slope of sheet conductance respect to logarithm of temperature become smaller implying that disorder is reduced by annealing. On the other hand, we compare experimental magnetoresistance with weak localization theory to obtain the spin-orbit scattering time (τso ) and inelastic scattering time (τin ) at temperature 0.3K~13K and in magnetic field 0Tesla~1Tesla. τin decreases as tCu decreases and τso is nearly a constant 0.5ps. Moreover, inelastic scattering rate 1/τin grows with increasing temperature as a function of (1/τin α T^P ) . P is around 2~3 by the non-linear least square fit. The value of P seems decreases with both increasing the slope of sheet conductance respect to ln(T) and decreasing diffusion constant D. That is, P is around 3 for systems in the clean limit, decreases gradually with increasing disorder, and then approaches to 2.