We study a class of photonic crystals in which both the dielectric constant e d the magnetic permeability m vary within the crystal. We find that in the case where both e andm have their maximum values in the same material, the photonic band gaps tend to disappear. However, in the opposite case where e andm have their maximum values in different materials, the gaps become wider with maximum gap over midgap frequency as high as 0.8. We also discuss the possibility of designing such photonic crystals with ferrites. @S0163-1829 ~97!06227-9# BRIEF REPORTS

Physical Review B

Journal of Applied physics,Vol.33 : 1962年に発表されたレオロジー関連の論文

Solid-state electronics

In this letter, we systematically investigate the impact of gate length and channel orientation on the electrical performance of tunneling field-effect transistors (TFETs). We fabricate and characterize Si/SiGe heterostructure TFETs with p-doped compressively strained Si
 0.5
Ge
 0.5
 source, intrinsic Si channel, and n-doped Si drain. We observe a linear relation of gate length, L
 g
, and ON-current, I
 ON
, which is the first experimental proof of line tunneling occurring in a TFET. TCAD simulations support our observations. After forming gas annealing, short-channel TFETs exhibit different I-V characteristics compared with long-channel devices due to better passivation.

Line and Point Tunneling in Scaled Si/SiGe Heterostructure TFETs

We report on experimental and simulated results of tunneling field-effect transistors (TFETs) with a Si channel and a strained Si1-xGex source. The fabricated TFET with a tensile strained Si channel shows comparably large on-currents and a subthreshold slope of 80 mV/dec at 300 K for a drain current range of three orders of magnitude. A novel TFET structure is proposed to enhance the on-currents by using a buried Si1-xGex source. The overlap between the top thin Si channel and the buried SiGe source increases the tunneling area. Simulations indicate that this structure significantly improves the performance.

An Improved Si Tunnel Field Effect Transistor With a Buried Strained $\hbox{Si}_{1-x}\hbox{Ge}_{x}$ Source

We investigate here the impact of the dopant concentration in the source and drain regions on the ambipolar behavior of band-to-band tunneling field-effect transistors with compressively strained Si0.5Ge0.5 channels grown on Si on insulator. Source and drain areas were formed by BF2+ and As+ ion implantation to doses of 1 × 1013, 1 × 1014, and 1 × 1015 cm−2. We show that the dopant concentration impacts the energy band alignment of source/drain and the channel region, and thus influences the tunneling current. The ambipolar device behavior is strongly reduced toward unipolar for source-to-drain implantation dose ratio of 100, but at the expense of the on-current, as compared to symmetric implanted devices. Moreover, our results indicate that for SiGe devices, the change of the B doping concentration has a greater impact on the tunneling currents than the variation of the As concentration.

/pdf/unipolar-behavior-of-asymmetrically-doped-strained-si0-5ge0-3uwrhyk38r.pdf

Unipolar behavior of asymmetrically doped strained Si0.5Ge0.5 tunneling field-effect transistors

Compressively strained Si 1−x Ge x band-to-band tunneling field effect transistors with planar structure and HfO 2 /TiN gate stack have been produced and analyzed, with different Germanium concentrations of x = 0.35, 0.50 and 0.65. Simulations using a nonlocal band-to-band-tunneling model have been carried out to understand the switching behavior and its dependence on the material parameters. One would expect an increase of the tunneling currents for the increase of x. However, the Si 0.5 Ge 0.5 devices show the highest I on and smallest S, whereas Si 0.35 Ge 0.65 devices exhibit decreased currents due to partial strain relaxation.

Impact of strain and Ge concentration on the performance of planar SiGe band-to-band-tunneling transistors

Compressively strained Si1−xGex band-to-band tunneling field effect transistors (TFETs) with planar structure are fabricated and analyzed. Different germanium concentrations of x = 0.35, 0.50 and 0.65 are investigated. An HfO2/TiN high-κ/metal gate stack is used for a better electrostatic control. The fabricated Si0.5Ge0.5 devices show the highest on-state current Ion and the smallest subthreshold slope (4 μA/μm and 162 mV/dec, respectively), whereas the performance of Si0.35Ge0.65 TFETs is degraded due to partial strain relaxation. The influences of Ge content and elastic strain, via band gap narrowing and effective mass change on the band to band tunneling effect are discussed. Simulations using a nonlocal band-to-band-tunneling model indicate that the transistor performance is enhanced with increasing Ge content and strain, in agreement with our experimental results.

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Unipolar behavior of asymmetrically doped strained Si0.5Ge0.5 tunneling field-effect transistors

Impact of strain and Ge concentration on the performance of planar SiGe band-to-band-tunneling transistors

Impact of strain and Ge concentration on the performance of planar SiGe band-to-band-tunneling transistors