Bulk PbSnSe has a two-phase region, or miscibility gap, as the crystal changes from a van der Waals-bonded orthorhombic 2D layered structure in SnSe-rich compositions to the related 3D-bonded rocksalt structure in PbSe-rich compositions. This structural transition drives a large contrast in the electrical, optical, and thermal properties. We realize low temperature direct growth of epitaxial PbSnSe thin films on GaAs via molecular beam epitaxy using an in situ PbSe surface treatment and show a significantly reduced two-phase region by stabilizing the Pnma layered structure out to Pb_0.45Sn_0.55Se, beyond the bulk limit around Pb_0.25Sn_0.75Se at low temperatures. Pushing further, we directly access metastable two-phase films of layered and rocksalt grains that are nearly identical in composition around Pb_0.50Sn_0.50Se and entirely circumvent the miscibility gap. We present microstructural and compositional evidence for an incomplete displacive transformation from a rocksalt to layered structure in these films, which we speculate occurs during the sample cooling to room temperature after synthesis. In situ temperature-cycling experiments on a Pb_0.58Sn_0.42Se rocksalt film reproduce characteristic attributes of a displacive transition and show a modulation in electronic properties. We find well-defined orientation relationships between the phases formed and reveal unconventional strain relief mechanisms involved in the crystal structure transformation using transmission electron microscopy. Overall, our work adds a scalable thin film integration route to harness the dramatic contrast in material properties in PbSnSe across a potentially ultrafast crystalline-crystalline structural transition.

中文翻译：

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层状 SnSe-PbSe 合金的扩展稳定性以及异质外延薄膜中岩盐位移相变的证据

块状 PbSnSe 具有两相区域或混溶间隙，因为晶体从富含 SnSe 成分中的范德华键合正交 2D 层状结构转变为富含 PbSe 成分中相关的 3D 键合岩盐结构。这种结构转变导致了电学、光学和热学性质的巨大反差。我们利用原位PbSe 表面处理，通过分子束外延在 GaAs 上实现了外延 PbSnSe 薄膜的低温直接生长，并通过将Pnma层状结构稳定到 Pb _0.45 Sn _0.55 Se来显着减少两相区，超出体相范围低温下限制在 Pb _0.25 Sn _0.75 Se 左右。更进一步，我们直接获得了层状和岩盐颗粒的亚稳态两相膜，它们在 Pb _0.50 Sn _0.50 Se 附近的成分几乎相同，并且完全规避了混溶性间隙。我们提供了这些薄膜中从岩盐到层状结构的不完全置换转变的微观结构和成分证据，我们推测这种转变发生在合成后样品冷却到室温期间。 Pb _0.58 Sn _{0.42 Se 岩盐薄膜的}原位温度循环实验再现了位移跃迁的特征属性，并显示了电子特性的调制。我们发现形成的相之间明确的取向关系，并使用透射电子显微镜揭示了涉及晶体结构转变的非常规应变消除机制。总体而言，我们的工作增加了一种可扩展的薄膜集成路线，以利用 PbSnSe 中材料特性的巨大对比，跨越潜在的超快晶体-晶体结构转变。