Electrical transport and noise in semiconducting carbon nanotubes

We investigate electrical transport and noise in semiconducting carbon nanotubes. By studying carbon nanotube devices with various diameters and contact metals, we show that the ON-currents of CNFETs are governed by the heights of the Schottky barriers at the metal/nanotube interfaces. The current fluctuations are dominated by 1/f noise at low-frequencies and correlate with the number of transport carriers in the device regardless of contact metal.     

Dopant segregation in SOI Schottky-barrier MOSFETs

We present experimental results on silicon-on-insulator Schottky-barrier MOSFETs with fully silicided NiSi source and drain contacts. Dopant segregation during silicidation was used to improve the device characteristics: on-currents, significantly higher than without dopant segregation as well as an almost ideal off-state are demonstrated in n-type as well as p-type SB-MOSFETs. Temperature dependent measurements show that the effective Schottky-barrier height in devices with segregation can be strongly lowered. In addition, we investigate the dopant segregation technique with simulations. Comparing simulations with experiments it turns out that the spatial extend of the segregation layer is on the few nanometer scale which is necessary for ultimately scaled devices. Furthermore, the use of ultrathin-body SOI in combination with ultrathin gate oxides results in an even further increased transmission through the Schottky barriers and consequently leads to strongly improved device characteristics. As a result, the dopant segregation technique greatly relaxes the requirement of low Schottky-barrier silicides for high performance transistor devices.     

Dislocation multiplication inside contact holes

Ion implantation into contact holes has been widely used to dope the specific contact area and to reduce the contact resistance. In this study, mask edge defects were observed at the edge area of small contact holes with high aspect ratio, which resulted in multiplied dislocations penetrating into Si substrate for more than 0.3 μm after back-end processings. Those dislocations were identified to be Schockley partial dislocations and stair rod dislocations lying on 4 sets of inclined {111}Si planes.     

Synthesis, reactions and structural features of monofluorinated cyclopropanecarboxylates

Monofluorinated cyclopropanecarboxylates are available in racemic or optically active form by transition metal-catalyzed reactions of vinylfluorides with diazoacetates. From α-fluorostyrene and tert-butyl diazoacetate in the presence of 2 mol% of an enantiopure bis(oxazoline) copper complex, a 81:19 mixture of tert-butyl trans- and cis-2-fluoro-2-phenylcyclopropanecarboxylates was obtained with high enantiomeric excess (ee) of 93 or 89%, respectively. The corresponding racemic ethylesters were used as starting materials for the synthesis of carboxamides, of the cis- and trans-isomers of analogues of tranylcypromine, an anti-depressive drug and several of its homologous fluorinated cyclopropylmethyl and cyclopropylethyl amines. Corresponding enantiopure cyclopropylmethanols and several of their derivatives were synthesized also. Solid state structures of a selection of these compounds were examined by X-ray crystallography. Particularly, the cis-configurated fluorinated phenylcyclopropane derivatives showed extremely close intermolecular CH?FC contacts. The shortest of such distances (2.17 Å) was found in the N-(4-bromophenyl)carbamate of (1S,2R)-(2-fluoro-2-phenylcyclopropyl)methanol.     

The effect of composition on the barrier height and contact resistance of Tixw1-x/si contacts

Barrier height is an important parameter for metal/silicon rectifying contacts. In this paper the barrier heights of Ti_xW{1-x}/Si contacts have been studied and found to range from 0.54 eV for high Ti content to 0.66 eV for pureW. Interpretation is made in terms of the parallel Schottky diode model of Tu. Ohmic contact measurements of Ti_xW_1-x/ Si metallization after heat treatment at 500° C have also been made and specific contact resistances of less than 10⁻⁶ ohm-cm² obtained in shallow implanted junction devices.     

The effect of Ti:W barrier metal on characteristics of palladium-silicide Schottky barrier diodes

The values of diode-quality factor and reverse-current leakage of Au/Pd/Ti:W/Pd₂Si/nSi unguarded Schottky barrier diodes are much higher than expected from silicide/silicon junction-radius induced highfield effects. Experimental Ti-, W-, and Ti:W-MIS structures were built and tested to show that Ti is responsible for the formation of a parasitic Ti-MIS structure around the unguarded-diode perimeter. This parasitic structure is responsible for excessive current leakage and also for an additional unguarded-diode degradation induced by annealing at 400 °C.     

Experimental and theoretical investigations of the electrical properties of undoped and magnesium-doped GaN layers

The ac characteristics of GaN : Mg and undoped GaN layers, grown by MOVPE on sapphire substrates, are measured for a wide range of temperature and bias conditions, in order to investigate the effect of the magnesium-related level on the transport properties. Two peaks, whose height and position depend on the measurement temperature, are observed in the admittance curves (G/ω versus frequency) of the Mg-doped samples, whereas only one peak appears in undoped samples. The study of the frequency dependence of the impedance, with a model including the two metallic Au/GaN junctions, the GaN layer itself, shows that, besides the effect of the differential resistance of the layer which plays a role in both sample types, the presence of a Mg-related deep level contributes to the observed variations of the peaks in the admittance curves of the p-doped samples. Results of a theoretical steady-state and small-signal analysis based on numerical modelling of the Au/GaN/Au heterostructure complete our analysis.     

Placement of Substrate Contacts to Minimize Substrate Noise in Mixed-Signal Integrated Circuits

The placement of substrate contacts in epi and non-epi technologies is analyzed in order to control and reduce the substrate noise amplitude and spreading. The choice of small or large substrate contacts or rings for each of the two major technologies is highlighted. Design guidelines for placing substrate contacts so as to improve the noise immunity of digital circuits in mixed-signal smart-power systems are also presented.     

Surface-layer damage and responsivity in sputtered-ITO/p-GaN Schottky-barrier photodiodes

It is postulated that donor-like nitrogen vacancies, caused by the sputtering of a Schottky-barrier metal onto p-type gallium nitride, diffuse into the GaN and form a surface layer in which both the minority-carrier lifetime and mobility are drastically reduced. Such a damaged surface layer is shown to reduce the responsivity of p-GaN Schottky-barrier photodiodes, thereby offering an explanation for the responsivity values in the range of 0.03–0.04 A/W that have been measured in experimental ITO/p-GaN devices. On making allowance for the damaged surface layer, an electron diffusion length of around 300 nm can be inferred for the undamaged p-GaN region.     

采用叠盖电极的高级长波60元光导探测器

介绍一种采用叠盖电极制备高级长波60元探测器的方法，并进行了较深入的实验，证明此方法是一种行之有效的提高光导探测器的技术。并在此基础上，确定了器件的最佳工作条件，而且证明应用有叠盖电极的器件是有方向性的。