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The impact of bulk and surface defect states on the vibrational and optical properties of step-graded epitaxial GaAs1-ySby (0 ≤ y ≤ 1) materials with and without chemical surface treatment by (NH4)2S was investigated. Tunable antimony (Sb) composition GaAs1-ySby epitaxial layers, grown by solid source molecular beam epitaxy (MBE), were realized on GaAs and Si substrates by varying key growth parameters (e.g., Sb/Ga flux ratio, growth temperature). Raman and photoluminescence (PL) spectroscopic analysis of (NH4)2S-treated GaAs1-ySby epitaxial layers revealed composition-independent Raman spectral widths and enhanced PL intensity (1.3×) following (NH4)2S surface treatment, indicating bulk defect-minimal epitaxy and a reduction in the surface recombination velocity corresponding to reduced surface defect sites, respectively. Moreover, quantification of the luminescence recombination mechanisms across a range of measurement temperatures and excitation intensities (i.e., varying laser power) indicate the presence of free-electron to neutral acceptor pair or Sb-defect-related recombination pathways, with detectable bulk defect recombination discernible only in binary GaSb PL spectra. In addition, PL analysis of the short- and long-term thermodynamic stability of sulfur-treated GaAs1-ySby/Al2O3 heterointerfaces revealed an absence of quantifiable atomic interdiffusion or native oxide formation. Leveraging the combined Raman and PL analysis herein, the quality of the heteroepitaxial step-graded epitaxial GaAs1-ySby materials can be optimized for optical devices. [ABSTRACT FROM AUTHOR]

The indirect nature of silicon (Si) emission currently limits the monolithic integration of photonic circuitry with Si electronics. Approaches to circumvent the optical shortcomings of Si include band structure engineering via alloying (e.g., Si x Ge 1- x - y Sn y ) and/or strain engineering of group IV materials (e.g., Ge). Although these methods enhance emission, many are incapable of realizing practical lasing structures because of poor optical and electrical confinement. Here, we report on strong optoelectronic confinement in a highly tensile-strained (ε) Ge/In 0.26 Al 0.74 As heterostructure as determined by X-ray photoemission spectroscopy (XPS). To this end, an ultrathin (∼10 nm) ε-Ge epilayer was directly integrated onto the In 0.26 Al 0.74 As stressor using an in situ, dual-chamber molecular beam epitaxy approach. Combining high-resolution X-ray diffraction and Raman spectroscopy, a strain state as high as ε ∼ 1.75% was demonstrated. Moreover, high-resolution transmission electron microscopy confirmed the highly ordered, pseudomorphic nature of the as-grown ε-Ge/In 0.26 Al 0.74 As heterostructure. The heterointerfacial electronic structure was likewise probed via XPS, revealing conduction- and valence band offsets (Δ E C and Δ E V ) of 1.25 ± 0.1 and 0.56 ± 0.1 eV, respectively. Finally, we compare our empirical results with previously published first-principles calculations investigating the impact of heterointerfacial stoichiometry on the ε-Ge/In x Al 1- x As energy band offset, demonstrating excellent agreement between experimental and theoretical results under an As 0.5 Ge 0.5 interface stoichiometry exhibiting up to two monolayers of heterointerfacial As-Ge diffusion. Taken together, these findings reveal a new route toward the realization of on-Si photonics., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

In this work, an in situ SiO 2 passivation technique using atomic layer deposition (ALD) during the growth of gate dielectric TaSiO x on solid-source molecular beam epitaxy grown (100)In x Ga 1- x As and (110)In x Ga 1- x As on InP substrates is reported. X-ray reciprocal space mapping demonstrated quasi-lattice matched In x Ga 1- x As epitaxy on crystallographically oriented InP substrates. Cross-sectional transmission electron microscopy revealed sharp heterointerfaces between ALD TaSiO x and (100) and (110)In x Ga 1- x As epilayers, wherein the presence of a consistent growth of an ∼0.8 nm intentionally formed SiO 2 interfacial passivating layer (IPL) is also observed on each of (100) and (110)In x Ga 1- x As. X-ray photoelectron spectroscopy (XPS) revealed the incorporation of SiO 2 in the composite TaSiO x , and valence band offset (Δ E V ) values for TaSiO x relative to (100) and (110)In x Ga 1- x As orientations of 2.52 ± 0.05 and 2.65 ± 0.05 eV, respectively, were extracted. The conduction band offset (Δ E C ) was calculated to be 1.3 ± 0.1 eV for (100)In x Ga 1- x As and 1.43 ± 0.1 eV for (110)In x Ga 1- x As, using TaSiO x band gap values of 4.60 and 4.82 eV, respectively, determined from the fitted O 1s XPS loss spectra, and the literature-reported composition-dependent In x Ga 1- x As band gap. The in situ passivation of In x Ga 1- x As using SiO 2 IPL during ALD of TaSiO x and the relatively large Δ E V and Δ E C values reported in this work are expected to aid in the future development of thermodynamically stable high-κ gate dielectrics on In x Ga 1- x As with reduced gate leakage, particularly under low-power device operation., Competing Interests: The authors declare no competing financial interest.