Mapping the Interfacial Electronic Structure of Strain-Engineered Epitaxial Germanium Grown on In_xAl_1–xAs Stressors

Abstract

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 Ge1–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/In0.26Al0.74As heterostructure as determined by X-ray photoemission spectroscopy (XPS). To this end, an ultrathin (∼10 nm) ε-Ge epilayer was directly integrated onto the In0.26Al0.74As 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/In0.26Al0.74As heterostructure. The heterointerfacial electronic structure was likewise probed via XPS, revealing conduction- and valence band offsets (ΔE C and ΔE 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 Al1–x As energy band offset, demonstrating excellent agreement between experimental and theoretical results under an As0.5Ge0.5 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.

High carrier lifetimes in epitaxial germanium–tin/Al(In)As heterostructures with variable tin compositions

“…Hence, by exploiting the Ge 1Ày Sn y /In x Al 1Àx As heterostructure, Ge 1Ày Sn y -based tunablewavelength photodetector and laser structures could be realized that would address many of the aforementioned issues, such as prohibitively high defect and dislocation densities, and their associated reduction in the minority carrier lifetime and increase in junction leakage. The reduced junction leakage can be achieved by growing a lattice-matched In x Al 1Àx As barrier underneath the Ge 1Ày Sn y active region, and increased band offsets between Ge 1Ày Sn y and In x Al 1Àx As (e.g., DE V = 0.49 eV and DE C = 1.01 eV for Ge/AlAs) 56 for electronic transport. Although extensive work has been performed in the direct integration of Ge 1Ày Sn y on Si, there is a lack of literature on the minority carrier lifetimes in Ge 1Ày Sn y materials as a function of the Sn alloy composition.…”

“…The reduced junction leakage can be achieved by growing a lattice-matched In x Al 1− x As barrier underneath the Ge 1− y Sn y active region, and increased band offsets between Ge 1− y Sn y and In x Al 1− x As ( e.g. , Δ E V = 0.49 eV and Δ E C = 1.01 eV for Ge/AlAs) 56 for electronic transport. Fig.…”

“…1(b) shows the schematic of the band alignment of Ge 1− y Sn y /In x Al 1− x As heterostructures with selected Sn compositions from 0 to 15%. The band alignments of the starting Ge/AlAs 56 and ε-Ge/In 0.26 Al 0.74 As 52 heterostructures, experimentally demonstrated via X-ray photoelectron spectroscopy, were used. Moreover, the change in Δ E V was relatively insignificant compared to Δ E C with increasing In compositions in In x Al 1− x As.…”

Atomic layer deposited tantalum silicate on crystallographically-oriented epitaxial germanium: interface chemistry and band alignment

“…To evaluate the valence band discontinuity (DE V ) at the TaSiO x dielectric/semiconductor interface, XPS spectra were recorded from: (i) nominally 5 nm (Ta 2 O 5 ) 1Àx (SiO 2 ) x on crystallographicallyoriented (001)Ge, (110)Ge, and (111)Ge, i.e., ''bulk-like'' TaSiO x ; (ii) nominally 1.5 nm (Ta 2 O 5 ) 1Àx (SiO 2 ) x on crystallographicallyoriented (001)Ge, (110)Ge, and (111)Ge, i.e., the oxide/semiconductor interface; and (iii), the surface of the as-grown (001)Ge, (110)Ge, and (111)Ge thin-films integrated on GaAs, i.e., ''bulklike'' Ge. Eqn (1), following the methodology developed by Kraut et al 75 as utilized in previous studies, 50,54,56,59,[76][77][78][79][80] was used to determine the DE V :…”

“…Lastly, as discussed in the Experiments section, we note that statistical deviation in the Au 4f 7/2 CL BE of a Au standard was utilized in the derivation of a AE0.04 eV experimental uncertainty for this work, from which successive uncertainty was estimated using a root-sum-square approach. [78][79][80] B.1. Energy band alignment at the TaSiO x /(001)Ge heterointerface.…”