Molecular beam epitaxy and defect structure of Ge (111)/epi-Gd2O3 (111)/Si (111) heterostructures

Abstract

Molecular beam epitaxy of Ge (111) thin films on epitaxial-Gd 2 O 3 /Si(111) substrates is reported, along with a systematic investigation of the evolution of Ge growth, and structural defects in the grown epilayer. While Ge growth begins in the Volmer-Weber growth mode, the resultant islands coalesce within the first ~ 10 nm of growth, beyond which a smooth two-dimensional surface evolves.Coalescence of the initially formed islands results in formation of rotation and reflection microtwins, which constitute a volume fraction of less than 1 %. It is also observed that while the stacking sequence of the (111) planes in the Ge epilayer is similar to that of the Si substrate, the (111) planes of the Gd 2 O 3 epilayer are rotated by 180° about the [111] direction. In metal-semiconductor-metal schottky photodiodes fabricated with these all-epitaxial Ge-on-insulator (GeOI) samples, significant suppression of dark current is observed due to the presence of the Gd 2 O 3 epilayer. These results are promising for application of these GeOI structures as virtual substrates, or for realization of high-speed group-IV photonic components.

Improvement of crystal quality and surface morphology of Ge/Gd2O3/Si(111) epitaxial layers by cyclic annealing and regrowth

“…Of the lanthanide oxides, Gd 2 O 3 is particularly promising, owing to the fact that gadolinium (Gd) exists only in one valence state (+3), thus rendering the sesquoxide the only stable oxide of Gd. Previous works [27][28][29][30], including an earlier report from our group [29], have convincingly established the feasibility of Ge(111) epitaxy on Gd 2 O 3 (111)/Si(111) engineered substrates, and have also investigated the crystalline quality and defect structure of the Ge layers in significant detail. Here, we report the impact of post-growth cyclic annealing (PGCA), and subsequent Ge re-growth at different temperatures, on the crystal structure and surface morphology of relatively-thick (⩾1 µm) Ge/Gd 2 O 3 /Si(111) epitaxial layers.…”

“…T Ge ( 111) and (333) reflections of Ge, respectively, while figure 1(d) plots the full-width-at-half-maximum (FWHM) values of these intensity profiles, along with that of another (similarly-prepared) as-grown sample (denoted by X) of smaller thickness (360 nm), studied in our previous work [29]. The numbers in the parentheses denote the total thickness of the Ge(111) epilayers (t Ge ) for each sample.…”

“…When grown sufficiently thick, the lanthanide-oxide layers would also enable realization of all-epitaxial germanium-on-insulator templates, in a single MBE or CVD growth step. Epitaxial growth of several lanthanide oxides has been optimized in the past couple of decades [10][11][12][13][14][15][16][17][18][19][20][21][22], albeit reports on growth of Ge on such templates are still very scarce [2,[23][24][25][26][27][28][29][30]. Of the lanthanide oxides, Gd 2 O 3 is particularly promising, owing to the fact that gadolinium (Gd) exists only in one valence state (+3), thus rendering the sesquoxide the only stable oxide of Gd.…”

Wafer-scale all-epitaxial GeSn-on-insulator on Si(1 1 1) by molecular beam epitaxy

“…The right inset shows the  rocking-curve diffractogram for the GeSn (111) peak, revealing a full-width-at-halfmaximum (FWHM) value of 0.57. This value is twice that of the FWHM measured for Ge epilayers grown on the same substrates earlier[30]. To determine the lattice constant(s) and the strain state of the GeSn epilayer, skew symmetric θ-2θ scans were recorded for the (224), (220) and (02 ̅ 6) reflections.…”

Metal semiconductor metal photodiodes based on all-epitaxial Ge-on-insulator-on- Si(111), grown by molecular beam epitaxy

“…The streaky pattern of Fig.1(d) persists till the end of Ge growth. More details on the growth and structural characterization of Ge(111)/Gd 2 O 3 (111)/Si(111) can be found in reference[13].…”