A new phenomenon of highly localized, nanoscale oxidation of silicon-containing layers has been observed. The localized oxidation enhancement observed in both Si and Si(3)N(4) layers appears to be catalyzed by the migration of Ge quantum dots (QDs). The sizes, morphology, and distribution of the Ge QDs are influenced by the oxidation of the Si-bearing layers. A two-step mechanism of dissolution of Si within the Ge QDs prior to oxidation is proposed.

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We report a first-of-its-kind, unique approach for generating a self-aligned, gate-stacking heterostructure of Ge quantum dot (QD)/SiO2/SiGe shell on Si in a single fabrication step. The 4-nm-thick SiO2 layer between the Ge QD and SiGe shell fabricated during the single-step process is the result of an exquisitely controlled dynamic balance between the fluxes of oxygen and silicon interstitials. The high-quality interface properties of our “designer” heterostructure are evidenced by the low interface trap density of as low as 2–4 × 1011 cm−2 eV−1 and superior transfer characteristics measured for Ge-based metal-oxide-semiconductor field-effect transistors (MOSFETs). Thanks to the very thin interfacial SiO2 layer, carrier storage within the Ge QDs with good memory endurance was established under relatively low-voltage programming/erasing conditions. We hope that our unique self-aligned, gate-stacking heterostructure provides an effective approach for the production of next-generation, high-performance Ge gate/SiO2/SiGe channel MOSFETs.

We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/ SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe-nanopatterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5-90 nm), the SiO2 thickness (3-4 nm), and the SiGeshell thickness (2-15 nm) have been demonstrated, enabling a practically achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive X-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5 × 10 11 cm −2 eV −1 and fixed charge densities of 1-5 × 10 11 cm −2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1−xGex shell (x > 0.5) in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge) MOS nanoelectronic and nanophotonic applications.

We demonstrate an effective approach to grow high-quality thin film (>1  μm) of multifold Ge/Si/Ge composite quantum dots (CQDs) stacked heterostructures for near infrared photodetection and optical interconnect applications. An otherwise random, self-assembly of variable-fold Ge/Si CQDs has been grown on Si through the insertion of Si spacer layers to produce micron-scale-thick, stacked Ge/Si CQD layers with desired QD morphology and composition distribution. The high crystalline quality of these multifold Ge CQD heterostructures is evidenced by low dark current density of 3.68  pA/μm2, superior photoresponsivity of 267 and 220 mA/W under 850 and 980 nm illumination, respectively, and very fast temporal response time of 0.24 ns measured on the Ge/Si CQD photodetectors.