ALBERT

Notes: A multi-ion-beam reactive sputter (MIBERS) deposition technique was devised to grow ferroelectric lead zirconate titanate (PZT) thin films of different compositions (Zr/Ti ratios of 50/50 and 56/44) from individual metal targets of Pb, Zr, and Ti. This technique offers a highly controllable deposition process allowing excellent uniformity in composition and thickness over a large area (7.5 cm diameter) on a reproducible basis. The PZT films were deposited on a variety of unheated substrates and annealed by two different techniques, rapid thermal annealing and conventional furnace annealing. Both techniques induced a perovskite phase with good morphology. The effect of the excess Pb content was observed in terms of the crystallization and morphology. It was seen that the presence of excess Pb tends to enhance perovskite phase formation but degrades the morphology. The effect of the substrates was observed in terms of crystallization and orientation. A low-energy oxygen ion beam was employed to modify the film growth. Secondary-ion bombardment seems to be a promising approach to optimize the film quality as it showed a variety of effects such as enhancing crystallization, inducing preferred orientation, and improving the film morphology. The present MIBERS-grown PZT films showed fairly high dielectric constants, about 850 for PZT (50/50) and about 1150 for PZT (56/44), and low dielectric losses. Ferroelectricity of these films was established with the values of the remnant polarization and the coercive field for PZT (50/50) of 23 μC/cm2 and 80 kV/cm and for PZT (56/44) of 20 μC/cm2 and 60 kV/cm, respectively. The low-energy oxygen ion-beam bombardment during the growth of PZT (50/50) films caused an increase in the dielectric constant to about 1000, reduction in the dissipation factor to 0.02, increase in the remnant polarization to about 26 μC/cm2, and decrease in the coercive field to about 60 kV/cm. The C-V characteristics of PZT (50/50) films in a metal-ferroelectric-metal configuration also indicated a clear dielectric polarization hysteresis.

Notes: The relation between gold related levels in silicon is studied with deep level transient spectroscopy (DLTS) using linearly graded junctions. Since the depletion layer extends equally on both sides in the linearly graded junction, both the acceptor level in the upper half and the donor level in the lower half of the band gap are simultaneously monitored as majority-carrier traps. It is observed that the concentration of the acceptor level is about four times more than the donor level. The defect concentrations have been calculated using modified DLTS theory for linearly graded junctions where the influence of free-carrier tail has been properly considered for both the traps. The difference in concentrations indicates that the two deep levels originate from different configurations of the gold impurity in silicon.

Notes: Trapping characteristics of two peaks, named A and B, associated with the well-known DX center in molecular-beam epitaxial grown, silicon-doped AlxGa1−xAs (x=0.36) are studied by deep-level transient spectroscopy as function of filling pulse width. With increase in filling pulse duration, several interesting features are noted including interdependence of the two peaks apparently logarithmic increase in height, shift in the peak temperature of the low-temperature peak B, and sharp reduction in its width. These unusual features provide clues to the dynamics of carrier capture and emission at the defect. We propose a model to qualitatively explain these features.

Notes: The phenomenon of two-stage photoquenching of EL2 defect in semi-insulating GaAs [V. Pandian and V. Kumar, J. Appl. Phys. 70, 5114 (1991)] is further investigated by sequentially irradiating the sample with different energy photons in the quenching band at constant temperature. The results of the new experiments, which are similar to the sequential quenching experiments with fixed photon energy at different temperatures, support the conclusion that the two-stage quenching may be related to the possible lattice strain mediated cooperative structural distortion arising out of transition of EL2 to the metastable state.

Notes: The photoquenching of EL2 in semi-insulating gallium arsenide is seen to be a complex process, where at low temperatures the initial slow quenching is followed by a switch to fast quenching. A possible explanation involving lattice strain mediated cooperative structural relaxation arising out of transition to the metastable state is proposed.

Notes: The evidence of interaction of gold-related defects with irradiation-induced defects in silicon is presented. It is observed that the concentrations of both the gold-related levels increase with increasing dose of irradiation. The linear relation between gold-related acceptor concentration NAu and the divacancy NV-V suggests that the gold-related level is a gold-divacancy complex rather than gold-vacancy complex.

Notes: In this paper we show that the analysis of the dynamics in localized regions, i.e., sub-systems can be used to characterize the chaotic dynamics and the synchronization ability of the spatiotemporal systems. Using noisy scalar time-series data for driving along with simultaneous self-adaptation of the control parameter representative control goals like suppressing spatiotemporal chaos and synchronization of spatiotemporally chaotic dynamics have been discussed. © 1998 American Institute of Physics.

Notes: A metallization scheme consisting of Ti/Al/Mo/Au with excellent edge acuity has been developed for obtaining low-resistance ohmic contacts to n–GaN. Excellent ohmic characteristics with a specific contact resistivity as low as 4.7×10−7 Ω-cm2 were obtained by rapid thermal annealing of evaporated Ti/Al/Mo/Au at 850 °C for 30 sec in a N2 ambient. Additionally, no degradation in specific contact resistivity was observed for these contacts subjected to long-term annealing at 500 °C for 360 h. © 2002 American Institute of Physics.

Notes: Most conducting organic materials have a background p-type doping varying in the range 1015–1017 cm−3. We report results of a theoretical and experimental study of carrier transport in p-doped organic Schottky diodes. The theory given in this article shows that in a doped organic material with ohmic contacts the current is ohmic at low voltages. If the ohmic contact at the cathode is replaced by an Al Schottky contact the current varies exponentially with the applied voltage V. The current changes to space charge limited current (SCLC) at high voltages. The voltage at which the change takes place depends on the doping concentrations. In the SCLC regime the current varies according to the well-known V2 law if there are no traps and the mobility is independent of the electric field. If either trapping or effect of field on mobility is important, the current varies as Vm, where m〉2. We have investigated experimentally the I–V characteristics of Schottky diodes fabricated using the PPV-based oligomer 2,5-di-n-octyloxy-1,4-bis (4′, 4″-bis-styryl) styrylbenzene (Ooct-OPV5) blended with polystyrene (PS) and the PPV-based polymer poly(2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene vinylene) (OC1C10). As predicted by the theory, Al/Ooct-OPV5:PS/ITO (indium tin oxide) and Al/OC1C10/ITO Schottky diodes do show that the current varies exponentially with V at low voltages and as SCLC according to the Vm law (with m=3) at high voltages. The V3 variation of the current in the SCLC regime can be due to trapping or field dependent mobility. It is not possible to distinguish unambiguously between the two mechanisms using the experimental results. The voltage at which transition from the Shockley current to SCLC takes place can be used to determine the background doping concentration. The p-type background doping concentration in the Ooct-OPV5 is found to be ∼1017 cm−3. From the temperature variation of the hole current at low voltages, a value 0.53±0.1 eV is determined for the Schottky barrier height at the Al/Ooct-OPV5:PS contact. When image barrier lowering for 1017 cm−3 doping is taken into account, this value of the barrier height is in good agreement with the difference in the Al work function and highest occupied molecular orbital of the organic material. Finally we suggest that if the background doping concentration can be eliminated, the SCLC and light emission in the light-emitting diodes should occur at lower voltages. © 2001 American Institute of Physics.

Notes: The breakdown of Ne, Ar, and Xe gases at different pressures is studied by focusing a XeCl excimer laser in the presence of a static electric field transverse to the laser focus.