Volume 91, Issue 12, 15 June 2002
Index of content:
- DEVICE PHYSICS (PACS 85)
91(2002); http://dx.doi.org/10.1063/1.1471920View Description Hide Description
Defect generation in gate dielectric stacks under constant voltage stress is investigated. It is found that the stress induced electrical degradation in stacks is different than in the layer. The variation of the gate leakage current with different polarities shows different degradation characteristics after stress. Positive charge generation is also observed under both negative and positive gate voltage polarities. These degradation phenomena are explained by the composite effect of three components: neutral trap generation, electron trapping, and positive charge generation in the gate stacks.
91(2002); http://dx.doi.org/10.1063/1.1479464View Description Hide Description
Spin-dependent transport of the photoexcited electrons in the semiconductor (p-GaAs)/insulator metal (permalloy)junctions was investigated. As samples, homogeneous tunnelingjunctions were prepared on the flat and As-defect-free GaAs(111)B homoepitaxial surface by in situoxidation of the Al layer and successive metallization by permalloy deposition. Spin-polarized electrons were excited in the GaAs by circularly polarized light and injected into the permalloy layer. Since the permalloy has almost zero magnetic circular dichroism at the vicinity of the band gapenergy of GaAs, we can detect spin-dependent current exclusively. As a result, the energy dependence of the observed helicity asymmetry (1.44–3.05 eV) of the photoinduced current shows the absence of the spin-dependent tunneling in the sample. The importance of controlling the electron lifetime to obtain the spin-dependent tunneling was discussed.
91(2002); http://dx.doi.org/10.1063/1.1471385View Description Hide Description
The nonlinear electrical transport properties of metal-insulator-metal tunnel diodes based on a barrier of naturally grown niobium oxide have been measured at room temperature and analyzed. In most cases excellent agreement is found between the measured current-voltage characteristics and fits to the trapezoidal barrier model, over large ranges in conductance (up to several times the zero-bias value), and including the asymmetry induced by the differing electrodematerials,niobium and silver. Moreover, we find that an in situ, Ar plasma etch may be used to modify the tunnel barrier in a controlled fashion. Specifically, as the etch time is increased from 0 to 120 s, the barrier thickness is continuously reduced from ∼2.8 to 1.1 nm, while the barrier height at the base (Nb)electrode remains roughly constant at Simultaneously, the barrier height at the Ag counterelectrode is lowered from an initial value of 800 mV to the asymptotic value implied by the difference in work functions of the electrodematerials, namely,
91(2002); http://dx.doi.org/10.1063/1.1476084View Description Hide Description
Organic transistor based circuits that can be employed for chemical vapor sensing, are described. Such circuits have improved sensing characteristics in comparison with discrete transistor based sensors. Complementary ring oscillator based sensors have a stronger response to analytes such as octanol and allyl propionate compared to a single transistor. A fabrication process that combines organic semiconductor circuitry with Si is described. The design and advantages of adaptive differential amplifiers with high gain and feedback are described. Voltage gains of allow the detection of weak odorant inputs and the adaptive feedback allows for improved background elimination.
Bright and efficient exciplex emission from light-emitting diodes based on hole-transporting amine derivatives and electron-transporting polyfluorenes91(2002); http://dx.doi.org/10.1063/1.1481203View Description Hide Description
We report highly efficient and bright emission from exciplexes generated between a series of hole-transporting amine derivatives and two electron-transporting fluorene–dicyanophenyl (FCNP) copolymers. These exciplexes were formed at either the interface between tetraphenyldiamine-containing perfluorocyclobutane polymers and the FCNP copolymers, or in the blends of the FCNP copolymers with small molecule amine derivatives such as triphenylamine, -diphenyl--bis(3-methylphenyl)--biphenyl]--diamine, and -diphenyl--bis(1-naphthyl)--biphenyl]--diamine. The exciplex emission is largely dependent on the composition of the hole-transporting materials. The best device derived from these exciplexes demonstrated a very low turn-on voltage (2.8 V), a high external quantum efficiency (0.91%), and a high brightness of The desirable properties of these devices were attributed to the excellent electron transport ability of the FCNP copolymers.