Volume 107, Issue 10, 15 May 2010
Index of content:
107(2010); http://dx.doi.org/10.1063/1.3380528View Description Hide Description
High crystalline quality (BSTZ) thin films were epitaxially grown by pulsed laser deposition on (001) single crystal substrates. Their epitaxial nature was revealed by x-ray and electron diffraction. Thinnest film has largest out-of-plane lattice constant (4.135 Å) and tetragonality (1.06). Films are under compressive strain. Film thicknesses above were started to relax as revealed from reciprocal space mapping. Thicknesses deduced from x-ray diffraction and transmission electron microscopy methods are in good agreement. Critical thickness to relieve strain of the BSTZ film is about .
107(2010); http://dx.doi.org/10.1063/1.3427566View Description Hide Description
The ferroelectrichysteresis loops of ceramics were measured under sinusoidal electric fields in the range of frequency from 0.1 to 100 Hz and field from 5 to 55 kV/cm. The fitting results showed two linear relations existed between the logarithm of hysteresis area and the logarithm of the amplitude of field in the first and third field region. In the second region, no linear relation existed due to polarization reversal. These three-stage behaviors were distinct from the existing two-stage behaviors. The slopes in the third stage increase with the increasing of frequency, which can be attributed to dielectric loss under high frequency.
107(2010); http://dx.doi.org/10.1063/1.3427567View Description Hide Description
This paper presents a two-dimensional nonuniform model to calculate the quantum shot noise suppression (or Fano factor) for electron field emission from a single field emitter of two different shapes: Lorentzian and prolate spheroidal. Between them, the Lorentzian field emitter has a larger shot noise suppression. For a given sharp emitter at a fixed work function, there is a minimum value of the Fano factor, which is independent of the geometrical sharpness of the emitter, and it increases with larger work function. Comparison with the one-dimensional uniform model has implied that prior results had overestimated the shot noise suppression.
Trap states in AlGaN/GaN metal-oxide-semiconductor structures with prepared by atomic layer deposition107(2010); http://dx.doi.org/10.1063/1.3428492View Description Hide Description
Atomic layer deposition(ALD) of was used to prepare metal-oxide-semiconductor(MOS) devices on two different_AlGaN/GaN heterostructures, with and without a thin GaN cap layer. Their trapping effects were evaluated by the frequency dependent conductance measurement. The trap state density decreased sharply from at the energy of 0.27 eV to at 0.45 eV. The low trap state density and exactly exponential dependence of the trap state time constant on the gate voltage show a good quality of the gate oxide. The trap state density in the structure with a GaN cap is about 2–3 times lower than that in the structure without a cap, which might be due to the different and interface properties. The trap state density in the structures investigated is lower than those reported for the devices with the metal-organic chemical vapor deposition and Al-oxidized gate oxide. This shows an importance of the ALD technique for the preparation of high-performance AlGaN/GaN MOS transistors.