Non-diffraction guiding modes covering the full broad band of a photonic crystal with elliptical rods for TM mode are reported in this paper. All such modes can be used to effectively guide electromagnetic waves since they have near-zero group velocity components along the X direction. In the fourth dispersion surface of the photonic crystal, the two wide flat regions spanning the first Brillouin zone possess unique properties: one dimension corresponds to a broad band, while the other corresponds to full incident angles of 0-90 •. These properties have many potential applications; as an example, here a broadband all-angle supercollimation with a bandwidth of 169 nm around 1550 nm is demonstrated. For the inverted structure of elliptical holes in a dielectric, similar results can be achieved over 140 nm around 1550 nm for TE mode.
This investigation proposes the improved double δ-doped InGaP/InGaAs heterostructure field-effect transistor (HFET) grown by metalorganic chemical vapour deposition. The extrinsic transconductance (g m) and saturation current density (I max) of the double δ-doped InGaP/InGaAs HFET are superior to those of the previously reported single δ-doped InGaP/InGaAs HFETs. The first n-InAlGaP/GaAs HFET is also investigated because it has a high Schottky barrier, a large high band gap and a large conduction-band discontinuity (E C). Even without indium in the channel of the InAlGaP/GaAs HFET, g m and I max are as high as 170 mS mm −1 and 410 mA mm −1 , respectively. The g m values of these two HFETs remain large even when the gate voltages are positive. Moreover, the breakdown voltages of the two examined HFETs both exceed 40 V.
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