Abstract-The current-voltage and noise characteristics of bridging silicon wires have been measured at room temperature. From the linear current-voltage characteristics the bulk and contact resistance contributions are extracted and modeled. The excess noise observed at low frequencies is interpreted in terms of bulk and contact noise contributions, with the former comparable, in terms of Hooge parameter values, to the low noise levels observed in high-quality silicon devices. The contact noise is significant in some devices and is attributed to the impinging end of the bridging nanowires.

Abstract:We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors. Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 x 10 7 cm/s at a low sheet charge density of 7.8 x 10 11 cm -2 . A new optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated LO phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.a)

The low frequency noise of single-walled carbon nanotubes is studied over the 77–300K temperature range. Lorentzian shaped spectra along with 1∕f noise spectra have been observed. From the Lorentzian noise components, a range of thermal activation energies from 0.08to0.51eV for the associated fluctuation mechanisms is obtained. From the 1∕f noise spectra, a distribution of activation energies of fluctuation processes ranging from 0.2to0.7eV is derived. These findings indicate that the observed noise spectra are caused by number fluctuations.

Due to the ultra‐wide bandgap of Al‐rich AlGaN, up to 5.8 eV for the structures in this study, obtaining low resistance ohmic contacts is inherently difficult to achieve. A comparative study of three different fabrication schemes is presented for obtaining ohmic contacts to an Al‐rich AlGaN channel. Schottky‐like behavior was observed for several different planar metallization stacks (and anneal temperatures), in addition to a dry‐etch recess metallization contact scheme on Al0.85Ga0.15N/Al0.66Ga0.34N. However, a dry etch recess followed by n+‐GaN regrowth fabrication process is reported as a means to obtain lower contact resistivity ohmic contacts on a Al0.85Ga0.15N/Al0.66Ga0.34N heterostructure. Specific contact resistivity of 5 × 10−3 Ω cm2 was achieved after annealing Ti/Al/Ni/Au metallization.