Liu Fengdeng, Golani Prafful, Truttmann Tristan K, Evangelista Igor, Smeaton Michelle A, Bugallo David, Wen Jiaxuan, Manjeshwar Anusha Kamath, May Steven J, Kourkoutis Lena F, Janotti Anderson, Koester Steven J, Jalan Bharat
Department of Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, Minneapolis, Minnesota 55455, United States.
Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities, Minneapolis, Minnesota 55455, United States.
ACS Nano. 2023 Sep 12;17(17):16912-16922. doi: 10.1021/acsnano.3c04003. Epub 2023 Aug 28.
The alkaline earth stannates are touted for their wide band gaps and the highest room-temperature electron mobilities among all of the perovskite oxides. CaSnO has the highest measured band gap in this family and is thus a particularly promising ultrawide band gap semiconductor. However, discouraging results from previous theoretical studies and failed doping attempts had described this material as "undopable". Here we redeem CaSnO using hybrid molecular beam epitaxy, which provides an adsorption-controlled growth for the phase-pure, epitaxial, and stoichiometric CaSnO films. By introducing lanthanum (La) as an n-type dopant, we demonstrate the robust and predictable doping of CaSnO with free electron concentrations, , from 3.3 × 10 cm to 1.6 × 10 cm. The films exhibit a maximum room-temperature mobility of 42 cm V s at = 3.3 × 10 cm. Despite having a comparable radius as the host ion, La expands the lattice parameter. Using density functional calculations, this effect is attributed to the energy gain by lowering the conduction band upon volume expansion. Finally, we exploit robust doping by fabricating CaSnO-based field-effect transistors. The transistors show promise for CaSnO's high-voltage capabilities by exhibiting low off-state leakage below 2 × 10 mA/mm at a drain-source voltage of 100 V and on-off ratios exceeding 10. This work serves as a starting point for future studies on the semiconducting properties of CaSnO and many devices that could benefit from CaSnO's exceptionally wide band gap.
碱土锡酸盐因其宽带隙以及在所有钙钛矿氧化物中具有最高的室温电子迁移率而备受关注。CaSnO在该族中具有最高的实测带隙，因此是一种特别有前景的超宽带隙半导体。然而，先前理论研究的令人沮丧的结果以及掺杂尝试的失败将这种材料描述为“不可掺杂的”。在这里，我们使用混合分子束外延技术挽救了CaSnO，该技术为纯相、外延且化学计量比的CaSnO薄膜提供了吸附控制生长。通过引入镧（La）作为n型掺杂剂，我们证明了CaSnO能够实现稳健且可预测的掺杂，自由电子浓度从3.3×10¹⁷ cm⁻³到1.6×10¹⁸ cm⁻³。这些薄膜在自由电子浓度为3.3×10¹⁷ cm⁻³时显示出最大室温迁移率为42 cm² V⁻¹ s⁻¹。尽管La与主体离子具有可比的半径，但它扩大了晶格参数。使用密度泛函计算，这种效应归因于通过体积膨胀降低导带而获得的能量。最后，我们通过制造基于CaSnO的场效应晶体管来利用稳健的掺杂。这些晶体管在漏源电压为100 V时表现出低于2×10⁻⁷ mA/mm的低关态泄漏电流以及超过10的开/关比，显示出CaSnO具有高压能力的前景。这项工作为未来关于CaSnO半导体特性以及许多可受益于CaSnO异常宽带隙的器件的研究奠定了基础。
