An unusual increase in the Seebeck coefficient with increasing charge carrier density is observed in pentacene thin film transistors. This behavior is interpreted as being due to a transition from hopping transport in static localized states to bandlike transport, occurring at temperatures below ∼250  K. Such a transition can be expected for organic materials in which both static energetic diso...

The doping dependence of specific heat and magnetic susceptibility has been investigated for Li(x)ZrNCl superconductors derived from a band insulator. As the carrier concentration is decreased, the anisotropy of superconducting gap changes from highly anisotropic to almost isotropic. It was also found that, upon reducing carrier density, the superconducting coupling strength and the magnetic su...

Anomalously large decrease in spontaneous emission is observed in gain-guided vertical-cavity surface-emitting lasers after the onset of lasing. By analyzing two-dimensional profiles of the lasing mode and carrier density, we found that this unexpected phenomenon originates from the contraction of transverse lasing mode size. Under the condition of the constant modal gain, it is explained that ...

Efficiency droop is a major obstacle facing high-power application of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs). In this paper, we report the suppression of efficiency droop induced by the process of density-activated defect recombination in nanorod structures of a-plane InGaN/GaN QWs. In the high carrier density regime, the retained emission efficiency in a dry-etched nanorod sa...

In this study, the properties of optically excited silicon were investigated using terahertz time-domain spectroscopy (THz-TDS). The surface was illuminated with 365-nm ultraviolet (UV) light to excite charge carriers, and properties such as conductivity, charge carrier density and mobility were evaluated. The illumination effect significantly changed the conductivity as well as the surface rec...

We attempt to understand the fundamental factors that determine the growth rate of carbon nanotubes. In a series of experiments on growing multiwall carbon nanotubes (MWNTs) by thermal chemical vapor deposition, we found that the addition of carrier gas and the type of carrier gas can change the growth rate, growth density, and structures of MWNTs. We explain these results based on the dissocia...

Collective impact ionization has been used to exT1ain lock-on in semi-insulating GaAs under highvohage bias. W7ehave used this theory to study some of the steady state properties of lock-on current filaments. In steady state, the heat gained from the field is exactly compensated by the cooling due to phonon scattering. In the simplest approximation, the carrier distribution approaches a quasi-e...