Department of Materials Science and Engineering and Materials Research Institute , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
ACS Appl Mater Interfaces. 2018 May 16;10(19):16623-16627. doi: 10.1021/acsami.8b02933. Epub 2018 May 7.
Germanium telluride (GeTe) is a phase change material (PCM) that has gained recent attention because of its incorporation as an active material for radio frequency (RF) switches, as well as memory and novel optoelectronic devices. Considering PCM-based RF switches, parasitic resistances from Ohmic contacts can be a limiting factor in device performance. Reduction of the contact resistance ( R) is therefore critical for reducing the on-state resistance to meet the requirements of high-frequency RF applications. To engineer the Schottky barrier between the metal contact and GeTe, Sn was tested as an interesting candidate to alter the composition of the semiconductor near its surface, potentially forming a narrow band gap (0.2 eV) SnTe or a graded alloy with SnTe in GeTe. For this purpose, a novel contact stack of Sn/Fe/Au was employed and compared to a conventional Ti/Pt/Au stack. Two different premetallization surface treatments of HCl and deionized (DI) HO were employed to make a Te-rich and Ge-rich interface, respectively. Contact resistance values were extracted using the refined transfer length method. The best results were obtained with DI HO for the Sn-based contacts but HCl treatment for the Ti/Pt/Au contacts. The as-deposited contacts had the R (ρ) of 0.006 Ω·mm (8 × 10 Ω·cm) for Sn/Fe/Au and 0.010 Ω·mm (3 × 10 Ω·cm) for Ti/Pt/Au. However, the Sn/Fe/Au contacts were thermally stable, and their resistance decreased further to 0.004 Ω·mm (4 × 10 Ω·cm) after annealing at 200 °C. In contrast, the contact resistance of the Ti/Pt/Au stack increased to 0.012 Ω·mm (4 × 10 Ω·cm). Transmission electron microscopy was used to characterize the interfacial reactions between the metals and GeTe. It was found that formation of SnTe at the interface, in addition to Fe diffusion (doping) into GeTe, is likely responsible for the superior performance of Sn/Fe/Au contacts, resulting in one of the lowest reported contact resistances on GeTe.
碲化锗（GeTe）是一种相变材料（PCM），由于其作为射频（RF）开关、存储器和新型光电设备的有源材料而受到关注。考虑到基于 PCM 的 RF 开关，欧姆接触的寄生电阻可能成为器件性能的限制因素。因此，降低接触电阻（R）对于降低导通电阻以满足高频 RF 应用的要求至关重要。为了对金属接触和 GeTe 之间的肖特基势垒进行工程设计，Sn 被测试为一种很有前途的候选材料，可以改变半导体表面附近的成分，从而有可能形成窄带隙（0.2 eV）的 SnTe 或 GeTe 中的 SnTe 梯度合金。为此，采用了新型的 Sn/Fe/Au 接触堆叠，并与传统的 Ti/Pt/Au 堆叠进行了比较。采用两种不同的预金属化表面处理盐酸（HCl）和去离子水（DI HO），分别形成富 Te 和富 Ge 的界面。使用改进的传输长度法提取接触电阻值。对于 Sn 基接触，使用 DI HO 获得了最佳结果，但对于 Ti/Pt/Au 接触，HCl 处理效果更好。对于沉积的接触，Sn/Fe/Au 的 R（ρ）为 0.006 Ω·mm（8×10 Ω·cm），Ti/Pt/Au 的 R（ρ）为 0.010 Ω·mm（3×10 Ω·cm）。然而，Sn/Fe/Au 接触具有热稳定性，在 200°C 退火后，其电阻进一步降低至 0.004 Ω·mm（4×10 Ω·cm）。相比之下，Ti/Pt/Au 堆叠的接触电阻增加到 0.012 Ω·mm（4×10 Ω·cm）。透射电子显微镜用于表征金属与 GeTe 之间的界面反应。发现界面处形成了 SnTe，以及 Fe 扩散（掺杂）进入 GeTe，这可能是 Sn/Fe/Au 接触具有优异性能的原因，使其成为报道的 GeTe 上最低接触电阻之一。
