Toru Kanazawa

InP/InGaAs Composite Metal–Oxide–Semiconductor Field-Effect Transistors with Regrown Source and Al2O3 Gate Dielectric Exhibiting Maximum Drain Current Exceeding 1.3 mA/µm

We have realized InP/InGaAs composite-channel metal–oxide–semiconductor field-effect transistors with both selectively regrown n+-InGaAs source/drain regions and Al2O3 as a gate dielectric. A 100-nm-long channel was fabricated by laterally buried regrowth in a channel undercut by metalorganic vapor phase epitaxy. The carrier density of the regrown layer was 2.9×1019 cm-3. A drain current Id of 1.34 mA/µm was achieved at a drain voltage Vd of 1 V and a gate voltage Vg of 3 V. A transconductance gm of 817 µS/µm at Vd = 0.65 V was also observed at the same time. The improvement in the subthreshold slope can be explained by the decrease in dielectric/semiconductor interface trap density.

Few-layer HfS2 transistors.

2D materials are expected to be favorable channel materials for field-effect transistor (FET) with extremely short channel length because of their superior immunity to short-channel effects (SCE). Graphene, which is the most famous 2D material, has no bandgap without additional techniques and this property is major hindrance in reducing the drain leakage. Therefore, 2D materials with finite band gap, such as transition metal dichalcogenides (TMDs, e.g. MoS2 WSe2) or phosphorene, are required for the low power consumption FETs. Hafnium disulfide (HfS2) is a novel TMD, which has not been investigated as channel material. We focused on its potential for well-balanced mobility and bandgap properties. The higher electron affinity of Hf dichalcogenides compared with Mo or W chalcogenides facilitates the formation of low resistance contact and staggered heterojunction with other 2D materials. Here we demonstrate the first few layer HfS2 FET with robust current saturation and high current on/off ratio of more than 10^4.HfS2 is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS2 has the potential for well-balanced mobility (1,800 cm2/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS2 flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS2 flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS2 transistor with the robust current saturation. The on/off ratio was more than 104 and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO4:PEO electrolyte, the drain current of the HfS2 transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm2/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS2. These results provides the basic information for the experimental researches of electron devices based on HfS2.

High drain current (>2A/mm) InGaAs channel MOSFET at V D =0.5V with shrinkage of channel length by InP anisotropic etching

In this paper, we report InGaAs channel MOSFETs with an InP source contact. InP source contact enables the suppression of carrier starvation and the easy shrinkage of the channel length by anisotropic etching. In fabricated 50-nm InGaAs channel MOSFETs, ID = 2.4A/mm at VD=0.5V were observed. On the other hand, degradations of Vth and SS by the short channel effect were also observed. Thinner channels will be required in order to suppress this effect.

Submicron InP/InGaAs Composite-Channel Metal?Oxide?Semiconductor Field-Effect Transistor with Selectively Regrown n+-Source

We have demonstrated an InP/InGaAs composite-channel metal–oxide–semiconductor field-effect transistor with a selectively regrown n+-InGaAs source/drain formed by metal organic vapor-phase epitaxy. A 150-nm-long channel was fabricated using a dummy gate and by laterally buried regrowth in the channel undercut. The gate stack was formed after regrowth by replacing the dummy gate. The carrier density of the regrown layer was 4.9×1019 cm-3. The maximum drain current at a drain voltage Vd = 1 V and a gate voltage Vg = 3 V was 0.93 mA/µm and the maximum transconductance was 0.53 mS/µm at Vd = 0.65 V.

Sub-50-nm InGaAs MOSFET with n-InP source on Si substrate

We demonstrated a sub-50-nm InGaAs 5-nm/InP 5-nm MOSFET with an n-InP source on a Si substrate using a 5-nm Al₂O₃ dielectric. In the measurement of the fabricated device, the maximum drain current and the peak transconductance at V_D = 0.5 V were 0.9 mA/μm and 0.8 mS/m, respectively. The threshold voltage was 0.09 V, and the drain-induced barrier lowering was 378 mV/V. From the channel length dependence, clear suppression of the short channel effect by the 5-nm-thick Al₂O₃ gate dielectric and the extremely thin body III-V-OI structure was confirmed.

InGaAs tri-gate MOSFETs with MOVPE regrown source/drain

InGaAs MOSFETs are attractive candidate for future high-speed and low-power-consumption devices. To enhance the performance of that, we propose a novel device structure which contains the superior current controllability due to the tri-gate structure and the high current drivability due to the n+-InGaAs source surrounding the non-planar channel. In this report, we demonstrate the source regrowth process for non-planar channel structure and current characteristics of the device fabricated by using regrowth.

Fabrication of thin-film HfS 2 FET

In conclusion, we demonstrated the fabrication and I-V characteristics of HfS2 FETs. For the channel thickness of less than 7.5 nm, a clear saturation behavior and drain current of 0.2 μA/μm were observed with reasonably good on/off current ratio. These results provide basic knowledge of HfS2 as a channel material for FET.

Optical Lattice Model Toward Nonreciprocal Invisibility Cloaking

We propose the design theory of nonreciprocal invisibility cloaking for an optical camouflage device with unidirectional transparency in which a person in the cloak can see the outside but cannot be seen from the outside. Existing theories of designing invisibility cloaks cannot be used for this purpose, because they are based on the transformation optics that uses the Riemannian metric tensor independent of direction. To realize nonreciprocal cloaking, we propose the theory of effective electromagnetic field for photons, which is an extended version of the theory of effective magnetic field for photons. The effective electromagnetic field can be generated using a photonic resonator lattice. The Hamiltonian for a photon in this field has a similar form to that of the Hamiltonian for a charged particle in an electromagnetic field. Incident photons, therefore, experience a Lorentz-like force and a Coulomb-like force and show nonreciprocal movement depending on their traveling direction. We design an actual invisibility cloaking system on the basis of this theory and, with the aid of computer simulation, confirm the nonreciprocal propagation of light needed for nonreciprocal cloaking.

Channel thickness dependence on InGaAs MOSFET with n-InP source for high current density

InGaAs is a promising material that can replace the current Si nMOSFET in CMOS because of its high electron mobility. To realize a high drain current density at a low supply voltage in InGaAs, the introduction of a heavily doped source is essential. We introduced an epitaxially grown n-InP source and obtained a high drain current density. However, short-channel effects were observed in a previous study; thus, we introduced extremely-thin-body III–V–OI InGaAs MOSFETs on a Si substrate. Accounting for the channel-thickness dependence, a drain current density of 2.04A/mm at VD F 0.5V and clear suppression of the short-channel effects were observed for a channel thickness of 10 nm.

Metamaterial Waveguide Devices for Integrated Optics

We show the feasibility of controlling the magnetic permeability of optical semiconductor devices on InP-based photonic integration platforms. We have achieved the permeability control of GaInAsP/InP semiconductor waveguides by combining the waveguide with a metamaterial consisting of gate-controlled split ring resonators. The split-ring resonators interact magnetically with light travelling in the waveguide and move the effective relative permeability of the waveguide away from 1 at optical frequencies. The variation in permeability can be controlled with the gate voltage. Using this variable-permeability waveguide, we have built an optical modulator consisting of a GaInAsP/InP Mach–Zehnder interferometer for use at an optical communication wavelength of 1.55 μm. The device changes the permeability of its waveguide arm with controlling gate voltage, thereby varying the refractive index of the arm to modulate the intensity of light. For the study of variable-permeability waveguide devices, we also propose a method of extracting separately the permittivity and permeability values of devices from the experimental data of light transmission. Adjusting the permeability of optical semiconductors to the needs of device designers will open the promising field of ‘permeability engineering’. Permeability engineering will facilitate the manipulation of light and the management of photons, thereby contributing to the development of novel devices with sophisticated functions for photonic integration.