黑磷雙閘極電晶體開發及研究

Abstract

在本論文中，我們提出一個方法解決在製作黑磷電晶體元件時，在通道與介電層會出現的介面問題。介面問題的主要原因是因為黑磷表面缺少未鍵結電子對(Lack of dangling bonds)，而現今解決方式主要分為兩種，第一種是使用同樣為二維材料的六方-氮化硼(Hexagonal Boron Nitride, h-BN)來取代傳統介電層(Al2O3, HfO2, etc.)；第二種是使用傳統介電層來完成元件。 首先，我們以h-BN當作介電層來製作黑磷電晶體。我們發現在使用氮化硼之後，可以觀察到元件載子遷移率的提升以及遲滯的下降。因為氮化硼表面同樣缺少未鍵結電子對，可以有效地減少通道表面散射。然而，h-BN厚度不易控制，並不適合用於往後的元件製作(top-gate FET, RF device, etc.)， 因此我們改用傳統的Al2O3來當作我們介電層。 Al2O3的成長是使用原子層沉積技術(Atomic layer deposition, ALD)。藉由調整成長參數，我們成功在黑磷上成長具有高品質的Al2O3。我們發現ALD的高溫成長過程，對黑磷電晶體的鍺金屬接點有退火的效果，透過EDX的分析我們可以發現鍺擴散進入黑磷的情形。除此之外，我們使用Raman並分析h-BN及Al2O3於大氣環境中對黑磷的保護程度。 透過高品質Al2O3的成長，我們不僅成功製成黑磷上閘極電晶體，也藉由下閘極的調變來得到黑磷雙閘極電晶體。我們藉由黑磷雙閘極電晶體的分析可以得到Al2O3的介電常數為9.6，此一結果高出許多先前的研究。我們也分析了黑磷雙閘極電晶體的控制機制，以及藉由雙閘極電晶體的結構，來達成黑磷的能隙調變。 綜合以上結果，我們得到了於黑磷上成長高品質Al2O3的方法，解決了黑磷通道和介電層的介面問題，並完成了黑磷雙閘極電晶體的量測與分析，進一步了解其控制機制及應用。

In this paper, we propose a method to solve the interface problem that occurs in the channel and dielectric layer when making black phosphorus field-effect transistor. The main reason for the interface problem is that the black phosphorus lacks of dangling bonds on its surface. Nowadays, there are two main solutions in this case. The first one is to replace the traditional dielectric layer (Al2O3, HfO2, etc.) with Hexagonal Boron Nitride (h-BN), which is also a two-dimensional material. The second one is using traditional dielectric layers to complete the components. First, we use h-BN as dielectric layer to make BP field-effect transistor. We have found that after the use of boron nitride, an increase in the mobility and a decrease in hysteresis can be observed. Because the boron nitride surface also lacks dangling bonds, BP channel surface scattering can be effectively reduced. However, h-BN thickness is not easy to control and is not suitable for top-gate FET (RF device, etc.), so we use traditional Al2O3 as our dielectric layer. Al2O3 is grown by Atomic layer deposition (ALD). By adjusting the growth parameters, we can grow high-quality Al2O3 on black phosphorus. After the growth of Al2O3, we found that the high temperature growth process of ALD has an annealing effect on the Germanium metal contact of the black phosphorus. Through the analysis of EDX, we can find that Germanium diffuses into black phosphorus. Furthermore, we used Raman to analyze the degree of protection of black phosphorus by h-BN and Al2O3 in the atmosphere. Finally, through the growth of high-quality Al2O3, we not only succeeded in making black phosphorus top-gate field-effect transistor, but also black phosphorus dual-gate gate transistor by the modulation of the bakc gate. We obtain a dielectric constant of 9.6 for Al2O3 by analysis of a black phosphorus dual-gate transistor. The dielectric constant result is much higher than many previous studies. We also analyzed the control mechanism of the black phosphorus dual-gate transistor and achieved the energy band gap modulation of black phosphorus. Based on the above results, we obtained a method for growing high-quality Al2O3 on black phosphorus, and solved the interface problem of black phosphorus channel and dielectric layer. We also completed the measurement and analysis of black phosphorus dual-gate transistor, and further understood its control mechanism and application.