Mean Free Path of Photoelectronic Excitations in Hydrogenated Amorphous Silicon and Silicon Germanium Alloy Semiconductors,Physica Status Solidi (B) - Basic Solid State Physics

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Mean Free Path of Photoelectronic Excitations in Hydrogenated Amorphous Silicon and Silicon Germanium Alloy Semiconductors
Physica Status Solidi (B) - Basic Solid State Physics ( IF 1.5 ) Pub Date : 2021-06-05 , DOI: 10.1002/pssb.202000473
Nikolas J. Podraza _{1,

2} , David B. Saint John ₃ , Maxwell M. Junda _{1,

2,

4} , Robert W. Collins _{1,

2}

Affiliation

Hydrogenated amorphous silicon germanium alloy (a-Si_1−xGe_x:H) films are prepared by plasma enhanced chemical vapor deposition (PECVD) and characterized by in situ real time spectroscopic ellipsometry (RTSE). From complex dielectric function spectra extracted, the broadening width energy (Γ) of the primary absorption feature centered near 3.7 eV is quantified using the Cody–Lorentz oscillator model. Mean free path length of photoelectronic excitations is calculated from Γ based on reasonable estimates for speed of electron–hole photoexcitations. A model is applied with excited state lifetime assumed to be limited by scattering from network disorder and provides a relative measure of short-range order. The simple model applied is an extension of that widely used to characterize broadening of optical transitions in polycrystalline semiconductors. Decreases in mean free path of up to ∼30% occur with germanium. Relative increases in mean free path with increased hydrogen during PECVD a-Si:H, a-Si_0.73Ge_0.27:H, and a-Si_0.60Ge_0.40:H occur from ∼5% to ∼8% and with hydrogen plasma treatment of a-Si:H by ∼6%. Mean free path changes are tracked with thickness to provide short range order evolution and the effect of the underlying material. Mean free path of photoexcitations in electronic quality a-Si_1−xGe_x:H is estimated at ∼3.5 Å, on the same order as interatomic spacing.

中文翻译：

氢化非晶硅和硅锗合金半导体中光电激发的平均自由程

氢化非晶硅锗合金 (a-Si _{1− x} Ge _x :H) 薄膜是通过等离子体增强化学气相沉积 (PECVD) 制备的，并通过原位实时光谱椭偏仪 (RTSE) 进行表征。从提取的复杂介电函数谱中，使用 Cody-Lorentz 振荡器模型量化中心在 3.7 eV 附近的主要吸收特征的展宽宽度能量 ( Γ )。光电子激发的平均自由程长度由Γ计算基于对电子-空穴光激发速度的合理估计。应用一个模型，假设激发态寿命受网络无序散射的限制，并提供了短程有序的相对度量。应用的简单模型是广泛用于表征多晶半导体中光学跃迁加宽的模型的扩展。锗的平均自由程减少高达 30%。PECVD 期间平均自由程随氢增加而增加 a-Si:H、a-Si _0.73 Ge _0.27 :H 和 a-Si _0.60 Ge _0.40:H 发生在~5% 到~8% 之间，氢等离子体处理 a-Si:H 时发生~6%。用厚度跟踪平均自由程变化，以提供短程阶次演变和底层材料的影响。电子质量 a-Si _{1− x} Ge _x :H 的平均光激发自由程估计为 ~3.5 Å，与原子间距相同。

更新日期：2021-06-05

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