Impact of Arsenic- and Indium-Terminated InGaAs Stressors on Carrier Confinement, Strain, Defects, and Transport Properties of Tensile-Strained Ge

Device-quality tensile-strained Ge (ε-Ge) grown on a large bandgap semiconductor with superior electrical and optical carrier confinement is essential for group-IV-based optoelectronics. Properties of ε-Ge active layers synthesized on In_0.24Ga_0.76As buffers with two different surface terminationsarsenic-rich and indium-richwere experimentally demonstrated, highlighting the factors not considered in theoretical calculations. High-resolution X-ray diffraction and Raman spectroscopy analyses of these ε-Ge/In_0.24Ga_0.76As heterostructures confirmed the fully strained (1.6%) and partially relaxed (0.82%) nature of the ε-Ge bonded with arsenic-terminated (Ge_{As‑terminated}) and indium-terminated (Ge_{In‑terminated}) In_0.24Ga_0.76As stressors, respectively. High-resolution cross-sectional transmission electron microscopy showed a coherent, sharp, and fully strained ε-Ge/In_0.24Ga_0.76As heterointerface in the Ge_{As‑terminated} heterostructure, whereas microtwin defects were present in the Ge_{In‑terminated} heterostructure. These heterostructures were further characterized by evaluating the minority carrier lifetimes, high for Ge_{As‑terminated} (525 ns) and low for Ge_{In‑terminated} (69 ns), using the photoconductive decay technique. Moreover, band alignment was constructed using X-ray photoelectron spectroscopy, where the Ge_{As‑terminated} heterostructure revealed that both holes and electrons were confined within the ε-Ge active layer as a type-I band alignment with Δ<i>E</i> _{V, As‑terminated} = 0.22 eV and Δ<i>E</i> _{C,As‑terminated} = 0.38 eV. On the other hand, the Ge_{In‑terminated} heterostructure exhibited a type-II band alignment with Δ<i>E</i> _{V,In‑terminated} = - 0.02 eV and Δ<i>E</i> _{C,In‑terminated} = 0.53 eV. Furthermore, the magnetotransport properties revealed high mobility (321 cm²/(V s)) with single-electron transport in Ge_{As‑terminated} heterostructure and low mobility (3.34 cm²/(V s)) with multihole transport in the Ge_{In‑terminated} heterostructure. Therefore, preferring the ε-Ge on the arsenic-rich surface of In_0.24Ga_0.76As stressor over the indium-rich surface during material synthesis offers device-quality materials with high carrier lifetime and superior carrier confinement, which can provide an opportunity to fabricate efficient group-IV-based optoelectronic devices.