School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287-1604, United States.
Department of Physics, Arizona State University , Tempe, Arizona 85287-1504, United States.
ACS Appl Mater Interfaces. 2017 Oct 11;9(40):35105-35113. doi: 10.1021/acsami.7b09272. Epub 2017 Sep 26.
Epitaxial synthesis of Ga(AsP)Ge alloys on Si(100) substrates is demonstrated using chemical vapor deposition reactions of [DGaN(CH)] with P(GeH) and As(GeH) precursors. These compounds are chosen to promote the formation of GaAsGe and GaPGe building blocks which interlink to produce the desired crystalline product. Ge-rich (GaP)Ge analogues have also been grown with tunable Ge contents up to 90% by reactions of P(GeH) with [DGaN(CH)] under similar deposition protocols. In both cases, the crystal growth utilized GeSi buffer layers whose lattice constants were specifically tuned as a function of composition to allow perfect lattice matching with the target epilayers. This approach yielded single-phase materials with excellent crystallinity devoid of mismatch-induced dislocations. The lattice parameters of Ga(AsP)Ge interpolated among the Ge, GaAs, and GaP end members, corroborating the Rutherford backscattering measurements of the P/As ratio. A small deviation from the Vegard's law that depends on the As/P ratio was observed and corroborated by ab initio calculations. Raman scattering shows evidence for the existence of Ga-As and Ga-P bonds in the Ge matrix. The As-rich samples exhibited photoluminescence with wavelengths similar to those observed for pure GaAsGe, indicating that the emission profile does not change in any measurable manner by replacing As by P over a broad range up to x = 0.2. Furthermore, the photoluminescence (PL) data suggested a large negative bowing of the band gap as expected on account of a strong valence band localization on the As atoms. Spectroscopic ellipsometry measurements of the dielectric function revealed a distinct direct gap transition that closely matches the PL emission energy. These measurements also showed that the absorption coefficients can be systematically tuned as a function of composition, indicating possible applications of the new materials in optoelectronics, including photovoltaics.
在 Si(100) 衬底上通过 [DGaN(CH)] 与 P(GeH) 和 As(GeH) 前体的化学气相沉积反应，成功地演示了 Ga(AsP)Ge 合金的外延合成。这些化合物的选择是为了促进 GaAsGe 和 GaPGe 构建块的形成，这些构建块相互连接以产生所需的结晶产物。通过 P(GeH) 与 [DGaN(CH)] 在类似的沉积条件下反应，也生长出了富 Ge 的 (GaP)Ge 类似物，其 Ge 含量可调谐高达 90%。在这两种情况下，晶体生长都利用了 GeSi 缓冲层，其晶格常数是根据组成专门调谐的，以允许与目标外延层完美的晶格匹配。这种方法得到了单相材料，具有极好的结晶度，没有失配诱导的位错。Ga(AsP)Ge 的晶格参数插值在 Ge、GaAs 和 GaP 端基之间，这与 Rutherford 背散射测量的 P/As 比相吻合。观察到了一个偏离 Vegard 定律的小偏差，该偏差取决于 As/P 比，并通过从头算计算得到了证实。拉曼散射证明了 Ga-As 和 Ga-P 键在 Ge 基质中的存在。富 As 样品表现出与纯 GaAsGe 相似的波长的光致发光，这表明在宽范围内（高达 x = 0.2）用 P 替代 As 时，发射轮廓没有以任何可测量的方式发生变化。此外，光致发光（PL）数据表明，由于价带在 As 原子上的强烈局域化，带隙的能带明显负弯曲。介电函数的光谱椭圆测量揭示了一个明显的直接带隙跃迁，与 PL 发射能密切匹配。这些测量还表明，吸收系数可以作为组成的函数进行系统地调谐，这表明新材料在光电学中的可能应用，包括光伏。
