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 In0.24Ga0.76As 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/In0.24Ga0.76As heterostructures confirmed the fully strained (1.6%) and partially relaxed (0.82%) nature of the ε-Ge bonded with arsenic-terminated (GeAs-terminated) and indium-terminated (GeIn-terminated) In0.24Ga0.76As stressors, respectively. High-resolution cross-sectional transmission electron microscopy showed a coherent, sharp, and fully strained ε-Ge/In0.24Ga0.76As heterointerface in the GeAs-terminatedheterostructure, whereas microtwin defects were present in the GeIn-terminatedheterostructure. These heterostructures were further characterized by evaluating the minority carrier lifetimes, high for GeAs-terminated(525 ns) and low for GeIn-terminated(69 ns), using the photoconductive decay technique. Moreover, band alignment was constructed using X-ray photoelectron spectroscopy, where the GeAs-terminatedheterostructure revealed that both holes and electrons were confined within the ε-Ge active layer as a type-I band alignment with ΔEV, As-terminated= 0.22 eV and ΔEC,As-terminated= 0.38 eV. On the other hand, the GeIn-terminatedheterostructure exhibited a type-II band alignment with ΔEV,In-terminated= – 0.02 eV and ΔEC,In-terminated= 0.53 eV. Furthermore, the magnetotransport properties revealed high mobility (321 cm2/(V s)) with single-electron transport in GeAs-terminatedheterostructure and low mobility (3.34 cm2/(V s)) with multihole transport in the GeIn-terminatedheterostructure. Therefore, preferring the ε-Ge on the arsenic-rich surface of In0.24Ga0.76As 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.