I. H. Chen

CMOS-Compatible Generation of Self-Organized 3-D Ge Quantum Dot Array for Photonic and Thermoelectric Applications

We demonstrate a CMOS-compatible scheme, selective oxidation of SiGe pillars, for creating well-organized 3-D Ge quantum dot (QD) array by guiding QDs migration along the oxidation path and thus placing them on targeted locations where the ultimate oxidation occurs. Stacked QDs exhibit tunable luminescence over the visible and possess low thermal conductivity, showing promise for nanophotonic and energy conversion devices.

Photoresponses in polycrystalline silicon phototransistors incorporating germanium quantum dots in the gate dielectrics

Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) incorporating germanium (Ge) quantum dots (QDs) in the gate oxide were fabricated as efficient blue to near ultraviolet phototransistors for light detection and amplification. Under 405–450 nm light illumination, Ge QDs poly-Si TFTs exhibit not only strong photoresponses in the drive current but also much improved subthreshold characteristics than that measured in darkness. This originates from the fact that only photoexcited holes within Ge QDs are injected into the active channel via vertical electric field and contribute excess mobile carriers for photocurrent but without the associated photogenerated electron induced junction barrier lowering.

Realization of solid-state nanothermometer using Ge quantum-dot single-hole transistor in few-hole regime

Semiconductor Ge quantum-dot (QD) thermometry has been demonstrated based on extraordinary temperature-dependent oscillatory differential conductance (GD) characteristics of Ge-QD single-hole transistors (SHTs) in the few-hole regime. Full-voltage width-at-half-minimum, V1/2, of GD valleys appears to be fairly linear in the charge number (n) and temperature within the QD in a relationship of eV1/2 ≅ (1 − 0.11n) × 5.15kBT, providing the primary thermometric quantity. The depth of GD valley is also proportional to charging energy (EC) and 1/T via ΔGD ≅ EC/9.18kBT, providing another thermometric quantity. This experimental demonstration suggests our Ge-QD SHT offering effective building blocks for nanothermometers over a wide temperature range with a detection temperature as high as 155 K in a spatial resolution less than 10 nm and temperature accuracy of sub-kelvin.

Single Germanium Quantum-dot Placement Along With Self-Aligned Electrodes for Effective Management of Single Charge Tunneling

We demonstrated the controlled placement of a Ge quantum dot (QD) along with tunnel-junction engineering in a self-organized approach for the effective management of single charge tunneling. In this approach, a single-Ge-QD ( ~ 11 nm) self-aligning with nickel-polycide electrodes is realized by thermally oxidizing a SiGe nanorod that bridges a 15-nm-wide nanotrench in close proximity to electrodes via a spacer bilayer of Si3N4/SiO2. The fabricated Ge-QD single-hole transistor exhibits clear Coulomb oscillation and Coulomb diamond behaviors at T = 77 K-150 K, providing a way to analyze the electronic structure of the Ge QD.

Internal structure and electrical properties of Ge quantum dot in single-electron transistors

We have developed a simple, manageable, and self-organized manner — thermally oxidizing SiGe nanocavity for precisely controlling Ge quantum dot (QD) number, position, and tunnel path, which is crucial for effective single-electron tunneling devices. The internal structure properties of Ge QDs were systematically characterized. The effectiveness of Ge QD placement is evidenced by high performance Ge QD single electron transistors (SETs), featuring with clear Coulomb staircase and Coulomb-blockade oscillation behaviors at room temperature.

Designer Ge quantum dots Coulomb blockade thermometry

A Coulomb blockade (CB) thermometer has been experimentally demonstrated based on the temperature dependence of a Ge quantum-dot (QD) single-hole transistor (SHT). The Ge-QD SHT features distinctive current peaks/plateaus, sharp differential conductance (G_D) dips up to temperature 120K. The full-width-at-half minimum, V_1/2, of the G_D dips directly scale with temperature following the material parameter-independent equation of eV_1/2 ~ 5.44k_BT, providing the primary thermometric quantity. Also the depths of the G_D dips increases with 1/k_BT as expected from CB theory of ΔG_D/G_D0 = E_C/6k_BT. This experimental demonstration indicates that our Ge-QD SHT offers an effective building block for ultrasensitive CB primary thermometers with the detection temperature as high as 115K.

Size Effects on Phase Formation and Electrical Robustness of Nickel Silicide Nanowires

We reported that the morphology, phase formation, and electrical resistivity of the NixSiy NW have strong dependences on the geometrical size of the as-formed Si NW before silicidation. The electrical current stressing generated selfheating and thus local compressive stress buildup and relaxation near the locations where the NixSiy NW ruptured.

Ultra-low Damage Fabrication of Graphene Nanoribbons by Neutral Beam Etching

Ultra-low-edge-defect graphene nanoribbons (GNRs) are successfully fabricated by subjecting large scale CVD graphene to a combination of electron beam lithography and oxygen neutral beam etching. Atomic force microscopy (AFM) images clearly show the morphology of the GNRs and Raman spectroscopy shows they have extremely low ID/IG ratio. A bottom-gate field-effect transistor with an array of the GNRs is found to have a high on/off ratio (~10 4 ) and high carrier mobility (~200 cm 2 V −1 s −1 ) even at room temperature.

Single Ge quantum dot placement along with self-aligned electrodes for effective management of single electron tunneling

We demonstrate controlled number and placement of the Ge quantum dot (QD) along with tunnel junction engineering through a self-organized approach for effective management of single electron tunneling. In this approach, a single Ge QD (~11 nm) self-aligning with nickel-silicide electrodes is realized by thermally oxidizing a SiGe nanorod bridging a 15-nm-wide nanotrench in close proximity to electrodes via a spacer bi-layer of Si3N4/SiO2. The fabricated Ge QD single electron transistor exhibits clear Coulomb staircase and Coulomb diamond behaviors at T = 120-300 K.

CMOS-compatible fabrication of room-temperature Ge QD single hole transistors

Precise control on quantum dot (QD) number and tunnel path in a self-organized manner is crucial for effective single electron tunneling. We experimentally demonstrated a single Ge QD (∼10 nm) self-aligned with nickel-silicide electrodes via Si3N4/SiO2 tunnel barriers by thermally oxidizing a SiGe nanorod. The fabricated Ge QD single hole transistor (SHT) features with clear differential conductance and Coulomb-blockade oscillation behaviors at near room temperature.