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

Abstract

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<inf>0.24</inf>Ga<inf>0.76</inf>As 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<inf>0.24</inf>Ga<inf>0.76</inf>As heterostructures confirmed the fully strained (1.6%) and partially relaxed (0.82%) nature of the ε-Ge bonded with arsenic-terminated (Ge<inf>As-terminated</inf>) and indium-terminated (Ge<inf>In-terminated</inf>) In<inf>0.24</inf>Ga<inf>0.76</inf>As stressors, respectively. High-resolution cross-sectional transmission electron microscopy showed a coherent, sharp, and fully strained ε-Ge/In<inf>0.24</inf>Ga<inf>0.76</inf>As heterointerface in the Ge<inf>As-terminated</inf>heterostructure, whereas microtwin defects were present in the Ge<inf>In-terminated</inf>heterostructure. These heterostructures were further characterized by evaluating the minority carrier lifetimes, high for Ge<inf>As-terminated</inf>(525 ns) and low for Ge<inf>In-terminated</inf>(69 ns), using the photoconductive decay technique. Moreover, band alignment was constructed using X-ray photoelectron spectroscopy, where the Ge<inf>As-terminated</inf>heterostructure revealed that both holes and electrons were confined within the ε-Ge active layer as a type-I band alignment with ΔE<inf>V, As-terminated</inf>= 0.22 eV and ΔE<inf>C,As-terminated</inf>= 0.38 eV. On the other hand, the Ge<inf>In-terminated</inf>heterostructure exhibited a type-II band alignment with ΔE<inf>V,In-terminated</inf>= – 0.02 eV and ΔE<inf>C,In-terminated</inf>= 0.53 eV. Furthermore, the magnetotransport properties revealed high mobility (321 cm²/(V s)) with single-electron transport in Ge<inf>As-terminated</inf>heterostructure and low mobility (3.34 cm²/(V s)) with multihole transport in the Ge<inf>In-terminated</inf>heterostructure. Therefore, preferring the ε-Ge on the arsenic-rich surface of In<inf>0.24</inf>Ga<inf>0.76</inf>As 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.