Reiner Maria, Pietschnig Rudolf, Ostermaier Clemens
Infineon Technologies Austria AG , Siemensstr. 2-5, 9500 Villach, Austria.
Institute of Chemistry and CINSaT, University of Kassel , Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
ACS Appl Mater Interfaces. 2015 Oct 21;7(41):23124-31. doi: 10.1021/acsami.5b06918. Epub 2015 Oct 9.
The influence of surface modifications on the Schottky barrier height for gallium nitride semiconductor devices is frequently underestimated or neglected in investigations thereof. We show that a strong dependency of Schottky barrier heights for nickel/aluminum-gallium nitride (0001) contacts on the surface terminations exists: a linear correlation of increasing barrier height with increasing electronegativity of superficial adatoms is observed. The negatively charged adatoms compete with the present nitrogen over the available gallium (or aluminum) orbital to form an electrically improved surface termination. The resulting modification of the surface dipoles and hence polarization of the surface termination causes observed band bending. Our findings suggest that the greatest Schottky barrier heights are achieved by increasing the concentration of the most polarized fluorine-gallium (-aluminum) bonds at the surface. An increase in barrier height from 0.7 to 1.1 eV after a 15% fluorine termination is obtained with ideality factors of 1.10 ± 0.05. The presence of surface dipoles that are changing the surface energy is proven by the sessile drop method as the electronegativity difference and polarization influences the contact angle. The extracted decrease in the Lifshitz-van-der-Waals component from 48.8 to 40.4 mJ/m(2) with increasing electronegativity and concentration of surface adatoms confirms the presence of increasing surface dipoles: as the polarizability of equally charged anions decreases with increasing electronegativity, the diiodomethane contact angles increase significantly from 14° up to 39° after the 15% fluorine termination. Therefore, a linear correlation between increasing anion electronegativity of the (Al)GaN termination and total surface energy within a 95% confidence interval is obtained. Furthermore, our results reveal a generally strong Lewis basicity of (Al)GaN surfaces explaining the high chemical inertness of the surfaces.
在对氮化镓半导体器件肖特基势垒高度的研究中，表面改性的影响常常被低估或忽视。我们表明，镍/铝 - 氮化镓（0001）接触的肖特基势垒高度强烈依赖于表面终端：观察到势垒高度随表面吸附原子电负性的增加呈线性相关。带负电荷的吸附原子与现有的氮争夺可用的镓（或铝）轨道，以形成电学性能改善的表面终端。由此导致的表面偶极子的改变以及表面终端的极化会引起观察到的能带弯曲。我们的研究结果表明，通过增加表面最极化的氟 - 镓（ - 铝）键的浓度可实现最大的肖特基势垒高度。在15％氟终端处理后，势垒高度从0.7 eV增加到1.1 eV，理想因子为1.10±0.05。由于电负性差异和极化会影响接触角，通过静滴法证明了改变表面能的表面偶极子的存在。随着电负性和表面吸附原子浓度的增加，从48.8到40.4 mJ/m²的Lifshitz - van der Waals分量的提取降低证实了表面偶极子的增加：随着等电荷阴离子的极化率随电负性增加而降低，在15％氟终端处理后，二碘甲烷接触角从14°显著增加到39°。因此，在95％置信区间内，（铝）氮化镓终端的阴离子电负性增加与总表面能之间存在线性关系。此外，我们的结果揭示了（铝）氮化镓表面普遍具有很强的路易斯碱性，这解释了表面的高化学惰性。
