G. Atiya

Electronic structure, morphology and emission polarization of enhanced symmetry InAs quantum-dot-like structures grown on InP substrates by molecular beam epitaxy

The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As2 source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model and realistic system parameters. The ...

A highly sensitive broadband planar metal-oxide-semiconductor photo detector fabricated on a silicon-on-insulator substrate

A high sensitivity photo-detector operating in the 245 to 880 nm wavelength range is reported. It is based on a planar Metal-Oxide-Semiconductor (MOS) structure fabricated on an insulator on silicon substrate where the insulator layer comprises a double layer dielectric stack of SiO2-HfO2. The MOS detector undergoes a voltage stress process after which it exhibits a record high responsivity of 0.4 A/W at 500–600 nm and 0.1 A/W at the spectrum edges, 245 and 880 nm. The structure is significantly simpler to fabricate than P-N or P-I-N junction devices and offers a lower dark current than Metal-Semiconductor-Metal diodes. Oxygen vacancies induced in the HfO2 sub-layer by the voltage stress form the conduction paths of the photo generated carriers. The penetration, under reverse bias conditions, of holes originating in the Si depletion layer is improved under illumination since their potential barrier is lowered. The compatibility with complimentary MOS technology processes makes this new structure attractiv...

Non-volatile memory transistor based on Pt nanocrystals with negative differencial resistance

We report on the structural and electrical characteristics of non-volatile memory (NVM) transistors and capacitors that use Pt nanocrystals (NCs) for charge storage. The transistor exhibits a memory window of 0.6 V for a sweep of ±2.5 V which increases to 11.5 V at ±10 V. The trapped charges (electron and hole) density for a ±10 V write/erase signal are 2.9 × 1013 cm−2. At small source to drain voltages (VSD) and for delay times longer than 0.1 ms, negative differential resistance (NDR) type behavior of the transistor source to drain ISD-VSD characteristics is revealed. The physical mechanism responsible for the NDR is related to the dynamics of electron injection (by tunneling through the thin bottom oxide) and their trapping by the Pt NCs. The large storage capability and relatively low program/erase voltages as well as the use of Pt, that is a Fab friendly material, make the described NVM transistors promising for practical applications.

Ultraviolet to near infrared response of optically sensitive nonvolatile memories based on platinum nano-particles and high-k dielectrics on a silicon on insulator substrate

An optically triggered nonvolatile memory based on platinum nano-particles embedded within a SiO2 and HfO2 dielectric stack on a silicon on insulator (SOI) substrate is presented. The memory cell exhibits a very wide spectral response, from 220 nm to 950 nm; much wider than common photo-detectors fabricated on SOI. It offers several functionalities including a low programming voltage and wide hysteresis of the capacitance-voltage characteristics, an illumination and voltage sweep amplitude dependent hysteresis of the current-voltage characteristics, and plasmonic enhanced, efficient broad-band photo detection.

Optically sensitive devices based on Pt nano particles fabricated by atomic layer deposition and embedded in a dielectric stack

We report a series of metal insulator semiconductor devices with embedded Pt nano particles (NPs) fabricated using a low temperature atomic layer deposition process. Optically sensitive nonvolatile memory cells as well as optical sensors: (i) varactors, whose capacitance-voltage characteristics, nonlinearity, and peak capacitance are strongly dependent on illumination intensity; (ii) highly linear photo detectors whose responsivity is enhanced due to the Pt NPs. Both single devices and back to back pairs of diodes were used. The different configurations enable a variety of functionalities with many potential applications in biomedical sensing, environmental surveying, simple imagers for consumer electronics and military uses. The simplicity and planar configuration of the proposed devices makes them suitable for standard CMOS fabrication technology.

Highly sensitive optically controlled tunable capacitor and photodetector based on a metal-insulator-semiconductor on silicon-on-insulator substrates

We describe a new type of optically sensitive tunable capacitor with a wide band response ranging from the ultraviolet (245 nm) to the near infrared (880 nm). It is based on a planar Metal-Oxide-Semiconductor (MOS) structure fabricated on an insulator on silicon substrate where the insulator layer comprises a double layer dielectric stack of SiO2-HfO2. Two operating configurations have been examined, a single diode and a pair of back-to-back connected devices, where either one or both diodes are illuminated. The varactors exhibit, in all cases, very large sensitivities to illumination. Near zero bias, the capacitance dependence on illumination intensity is sub linear and otherwise it is nearly linear. In the back-to-back connected configuration, the reverse biased diode acts as a light tunable resistor whose value affects strongly the capacitance of the second, forward biased, diode and vice versa. The proposed device is superior to other optical varactors in its large sensitivity to illumination in a ver...

Dynamical Properties of Optically Sensitive Metal-Insulator-Semiconductor Nonvolatile Memories Based on Pt Nanoparticles

We describe the optical properties of nonvolatile memory cells based on metal-insulator-semiconductor structures with embedded Pt nanoparticles, fabricated by atomic layer deposition. We show the effect of illumination on the static as well as dynamic properties of two devices, which differ by their respective thicknesses of the tunneling layer. The device with the thicker tunneling layer exhibits a faster response under illumination and significantly better retention properties, while the device with the thinner tunneling layer is faster under dark conditions.

Microstructure and phase composition in a die cast Mg–Nd alloy containing Zn and Zr

Abstract The microstructure of the as-cast Mg-3.1Nd-0.45Zr-0.25Zn (wt.%) alloy was investigated. It consists of α-Mg matrix, a divorced intergranular phase and small Zr-containing particles. Scanning electron microscopy equipped with energy dispersive spectroscopy analysis on transmission electron microscopy samples was carried out in order to eliminate the Mg matrix contribution to the quantitative analysis results and to reveal the intergranular phase composition which was found to be Mg12–xZnxNd (x ∼ 0.31) (space group I4/mmm) with a bct crystal structure. The lattice parameters (a = 1.029 nm and c = 0.591 nm) were found using X-ray diffraction with the least squares refinement technique. The combination of different characterization techniques indicates that Mg atoms are substituted by Zn atoms without a change in the crystal structure.

Non-volatile memory and negative photoconductivity in a metal-insulator-semiconductor diode with embedded Co nanoparticles

We describe a new metal-insulator-semiconductor (MIS) device in which cobalt based nano particles (NPs) in a core-shell structure (Co–core and Co3O4-shell) are embedded between a thermally grown SiO2 layer and a HfO2 film deposited by atomic layer deposition. Two additional structures were prepared for comparison. One had no NPs and the other included the Fe NPs, prepared using the same procedure as used for the Co film. All devices exhibited the classic behavior of a voltage variable MIS capacitor with or without a large hysteresis as in non-volatile memory (NVM) systems. However, only the device with the Co core-shell structure exhibits a negative photoconductivity (NPC) effect as well as NVM capabilities in both the capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The dependence of C-V and current voltage I-V characteristics on illumination intensity and wavelength (from ultraviolet to near infrared) as well as on temperature was characterized. Illumination enhances the NPC effect as well as the flat-band voltage shift determined from C-V characteristics and hence the memory width. Illumination in the wavelength range of 735–780 nm caused a current decrease, at a given voltage, by up to a factor of two. The NPC effect stimulates an annihilation of the stored charges and therefore erases the system instantly at a small applied bias. The main cause of the NPC effect under illumination is the photo excitation of supplementary trap channels in the Co3O4 shell, which lowers the free carrier density and hence the conductivity of the MIS structure.We describe a new metal-insulator-semiconductor (MIS) device in which cobalt based nano particles (NPs) in a core-shell structure (Co–core and Co3O4-shell) are embedded between a thermally grown SiO2 layer and a HfO2 film deposited by atomic layer deposition. Two additional structures were prepared for comparison. One had no NPs and the other included the Fe NPs, prepared using the same procedure as used for the Co film. All devices exhibited the classic behavior of a voltage variable MIS capacitor with or without a large hysteresis as in non-volatile memory (NVM) systems. However, only the device with the Co core-shell structure exhibits a negative photoconductivity (NPC) effect as well as NVM capabilities in both the capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The dependence of C-V and current voltage I-V characteristics on illumination intensity and wavelength (from ultraviolet to near infrared) as well as on temperature was characterized. Illumination enhances the NPC effect a...

Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles

This paper describes a metal-insulator-semiconductor (MIS) capacitor with flat capacitance voltage characteristics and a small quadratic voltage capacitance coefficient. The device characteristics resemble a metal-insulator-metal diode except that here the capacitance depends on illumination and exhibits a strong frequency dispersion. The device incorporates Fe nanoparticles (NPs), mixed with SrF2, which are embedded in an insulator stack of SiO2 and HfO2. Positively charged Fe ions induce dipole type traps with an electronic polarization that is enhanced by photogenerated carriers injected from the substrate and/or by inter nanoparticle exchange of carriers. The obtained characteristics are compared with those of five other MIS structures: two based on Fe NPs, one with and the other without SrF2 sublayers. Additionally, devices contain Co NPs embedded in SrF2 sublayers, and finally, two structures have no NPs, with one based on a stack of SiO2 and HfO2 and the other which also includes SrF2. Only structures containing Fe NPs, which are incorporated into SrF2, yield a voltage independent capacitance, the level of which can be changed by illumination. These properties are essential in radio frequency/analog mixed signal applications.