EXPERIMENTAL STUDIES OF BALLISTIC TRANSPORT IN SEMICONDUCTORS

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Abstract
The effects encountered with short-gate FET's in GaAs and In.53Ga.47 As/InP show some enhancement of average velocity, but effective electrical lengths are much longer than the gates. When N+ N N+ short, two-terminal devices, with. 36 µm electrical length, are tested at room temperature, the current density values allow one to infer an average velocity of about 4x107 cm/s for .35-.50 V bias. Using Gunn effect threshold experimental data at room temperature, it will be shown that the average distance between launching polar optical phonons is just over 1000 Å at electron energy values of ~.1 eV, and over 1500 Å at electron energy values of more than .3 eV and the most probable angle after scattering is small. Planar doped barrier (PDB) will be presented as ballistic electron launchers and collectors, for velocity near 1x108 cm/s. Using closely-spaced PDB's back to back, a ballistic injection and drift condition can be set up on opposite sides of an N base region, for very high frequency transistors. By scaling the finger size to the limits of photolithography (.75 µm), over 200 GHz fmax is expected in such transistors in the near future. Using buried metal submicron base fingers, up to 1000 GHz fmax is eventually expected

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