Structure and properties of Ta/Al/Ta and Ti/Al/Ti/Au multilayer metal stacks formed as ohmic contacts on n-GaN
Structure and properties of Ta/Al/Ta and Ti/Al/Ti/Au multilayer metal stacks formed as ohmic contacts on n-GaN
复制标题
在 n-GaN 上形成欧姆接触的 Ta/Al/Ta 和 Ti/Al/Ti/Au 多层金属堆叠的结构和性能
DOI：
10.1007/s10854-019-02167-2
复制
发表时间：
2019
期刊：
影响因子：
--
通讯作者：
V. Popok
中科院分区：
文献类型：
--
作者：
I. Boturchuk;T. Walter;B. Julsgaard;G. Khatibi;S. Schwarz;M. Stöger;K. Pedersen;V. Popok
GaN欧姆接触的形成对于器件制造具有很高的实际重要性。由于宽带隙，需要形成多层金属结构以形成具有低接触电阻的电连接。本文研究了用电子束蒸发和热退火方法制备的Ti/Al/Ti/Au和Ta/Al/Ta金属叠层的结构、成分、附着力和电学性能，以提供与Si上生长的n型GaN薄膜的欧姆接触。对于Ti基的情况下，发现Au和Ga的相互扩散到堆叠中，这可能是由于顶部Ti层的颗粒结构没有形成适当的阻挡层造成的。观察到底层的Ti扩散到GaN中，形成氮化钛薄层，其在GaN界面处具有低肖特基势垒，允许欧姆接触，如通过电测量所示。Ta基叠层具有预期的层状结构，在这两种金属的界面处具有Al和Ta的轻微相互扩散。没有观察到Ta扩散到GaN中的直接显微证据。然而，在GaN界面处形成的氮化钽薄层可以从电流-电压测量中推断出，欧姆电接触具有1.2 × 10−3 Ω cm 2的低接触电阻率。四点弯曲实验表明，裂纹总是在Si与GaN缓冲层的界面处产生。没有观察到金属化层的剥落，这允许我们得出关于金属叠层的良好粘附的结论。因此，所制造的Ti和Ta基多层结构显示出良好的电性能和可靠的附着力，使它们有希望形成欧姆接触到n型GaN。
Formation of ohmic contacts to GaN is of high practical importance for device fabrication. Due to the wide band gap, formation of multilayer metal structures is required to make electrical connections with low contact resistance. The paper presents a study on structure, composition, adhesion and electrical properties of Ti/Al/Ti/Au and Ta/Al/Ta metal stacks fabricated by e-beam evaporation and thermal annealing in order to provide ohmic contacts to n-type GaN films grown on Si. For the Ti-based case, an interdiffusion of Au and Ga into the stack is found, which is probably caused by a granular structure of the top Ti layer making no proper barrier. Ti of the bottom layer is observed to diffuse into GaN, forming a thin layer of titanium nitride with a low Schottky barrier at GaN interface allowing ohmic contact as shown by electrical measurements. The Ta-based stacks have the expected layered structure with minor interdiffusion of Al and Ta at the interfaces of these two metals. No direct microscopic evidences for Ta diffusion into GaN is observed. However, the formation of a thin tantalum nitride layer at the GaN interface can be deduced from the current–voltage measurements showing ohmic electrical contacts with low contact resistivity of 1.2 × 10−3 Ω cm2. Four-point bending tests on the both types of samples show that cracks always develop at the interface between Si and buffer layers of GaN. No exfoliation of the metallization layers is observed allowing us to conclude about good adhesion of the metal stacks. Thus, the fabricated Ti- and Ta-based multilayer structures show good electrical performance and reliable adhesion making them promising for the formation of ohmic contacts to n-type GaN.