Structural and electrical characteristics of epitaxial germanium (Ge) heterogeneously integrated on silicon (Si) via a composite, large bandgap AlAs/GaAs buffer are investigated. Electrical characteristics of N-type metal-oxide-semiconductor (MOS) capacitors, fabricated from the aforementioned material stack are then presented. Simulated and experimental X-ray rocking curves show distinct Ge, AlAs, and GaAs epilayer peaks. Moreover, secondary ion mass spectrometry, energy dispersive X-ray spectroscopy (EDS) profile, and EDS line profile suggest limited interdiffusion of the underlying buffer into the Ge layer, which is further indicative of the successful growth of device-quality epitaxial Ge layer. The Ge MOS capacitor devices demonstrated low frequency dispersion of 1.80% per decade, low frequency-dependent flat-band voltage, V FB , shift of 153 mV, efficient Fermi level movement, and limited C-V stretch out. Low interface state density (D it ) from 8.55 × 10 11 to 1.09 × 10 12 cm −2 eV −1 is indicative of a high-quality oxide/Ge heterointerface, an effective electrical passivation of the Ge surface, and a Ge epitaxy with minimal defects. These superior electrical and material characteristics suggest the feasibility of utilizing large bandgap III-V buffers in the heterointegration of high-mobility channel materials on Si for future high-speed complementary metal-oxide semiconductor logic applications.INDEX TERMS Germanium (Ge), heteroepitaxy, metal-oxide semiconductor (MOS) devices, silicon (Si), III-V materials.
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.
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