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The impact of a TaOx nanolayer at the GeSex/W interface on the performance of resistive switching memory in an Al/Cu/GeSex/TaOx/W structure has been examined. All materials and the memory structure have been investigated using high-resolution transmission electron microscopy, energy dispersive x ray spectroscopy, and x ray photo-electron spectroscopy analyses. A conically shaped crystalline Cu (111) nanofilament with a diameter of around 17 nm in the TaOx nanolayer after a current compliance (CC) of 500 μA has been observed, and this has been also characterized by fast Fourier transform. The low resistance state (LRS) decreases as the current compliances (CCs) increased from 1 nA to 1 mA, since the nanofilament diameter increased from 0.04 to 23.4 nm. This is also estimated by bipolar resistive switching characteristics. The resistivity of this crystalline Cu nanofilament is approximately 2300 μΩ.cm. The nanofilament has a cylindrical shape, with CCs ranging from 1 nA to 10 μA and a conical shape with CCs ranging from 50 μA-1 mA. The resistive switching mechanism has been explained successfully under SET and RESET operations. Improved resistive switching parameters, such as SET voltage, LRS, and high resistance state with consecutive switching cycles are obtained and compared to those of pure GeSex and TaOx materials. Extrapolated, long program/erase endurance of > 106 cycles, attributed to the Al/Cu/GeSex/TaOx/W structure design, is observed. This resistive switching memory structure shows extrapolated 10 years data retention with a resistance ratio of > 10 at a low CC of 0.1 μA at 50 °C. A large memory size of ∼ 6 Pbit/sq. in. is obtained, considering the nanofilament diameter at a low CC of 0.1 μA. This study is important not only for improving the performance of low-power resistive switching memory, but also helpful for designing other nonvolatile memory devices. [ABSTRACT FROM AUTHOR]

Presents a study that examined Al[subx]Ga[sub1-x]As double heterostructure light emitting diodes (LED) grown by liquid phase epitaxy. Behavior of LED fabricated from a crystal grown by metalorganic chemical vapor deposition; Effect of residual defects and competing nonradiative recombination; LED recombination-radiation spectra.

Pretreatment of silicon surface with SiCH6 was used to modify the Stranski-Krastanow growth mode of Ge on Si(001) at 550 °C by ultrahigh vacuum chemical vapor deposition. With the appropriate SiCH6 mediation, the elongated Ge hut clusters can be transformed to highly uniform multifaceted domes with a high Ge composition at the core. These SiCH6-mediated Ge dots have an average diameter and height of 38 and 7 nm, respectively. The modified growth mode for the formation of SiCH6-mediated Ge dots can be attributed to (i) an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation and (ii) the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. The results also demonstrate that SiCH6-mediated dots exhibit the improved field emission characteristics compared to shallow Ge huts. [ABSTRACT FROM AUTHOR]

Charge-trapping type flash memory devices with various integrations of metal gates having different work functions and blocking oxides were investigated in this work. Improved erasing speed together with acceptable reliability characteristics can be achieved by the integration of high work-function metal gate and high-k blocking oxide due to an efficient suppression of electron back tunneling through the blocking oxide during erasing operation for the MoN sample. Specifically, the high work-function value of MoN metal gate can be kept only by integrating with the Al2O3 blocking oxide because it can suppress the formation of molybdenum-silicide. Moreover, high-speed erasing can also be demonstrated by combining the MoN metal gate with an HfAlO charge trapping layer when band-to-band hot hole erasing method is adopted. [ABSTRACT FROM AUTHOR]

The physical and electrical characteristics of atomic layer deposited TiN nanocrystals embedded in high-k Al2O3 films in a metal/Al2O3/[TiN/Al2O3]/SiO2/p-Si structure have been investigated. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy show the formation of tiny TiN nanocrystals embedded in Al2O3 films after subsequent annealing treatment. The TiN nanocrystals with a high density of >1×1012/cm2 and a small size of <3 nm have been observed. A large hysteresis memory window of ∼4.3 V at small sweeping gate voltage of 3 V has been observed as compared with a pure Al2O3 charge trapping layer, due to highly charge confinement in the TiN metal nanocrystals. The hysteresis memory window of 1.4 V has also been observed under an extremely small sweeping gate voltage of 1 V. A large memory window of ∼3.9 V is observed after 10 years of retention. A maximum hysteresis memory window is limited by both of the nanocrystal density and leakage current at a high temperature annealing treatment of the TiN nanocrystal memory capacitors. [ABSTRACT FROM AUTHOR]

The band offsets and charge storage characteristics of atomic layer deposited high-k HfO2/TiO2 multilayers with ten periods in p-Si/SiO2/(HfO2/TiO2)/Al2O3 structure have been investigated. The thickness of high-k HfO2 or TiO2 film is ∼0.5 nm for each layer, before and after annealing treatment of 900 °C for 1 min in N2 ambient. High-resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy measurements on high-k HfO2/TiO2 multilayers confirm the layer-by-layer structure after annealing treatment, suggesting the HfO2/TiO2 multilayer quantum wells. The valence band offsets of HfO2 and TiO2 films are found to be ∼3.1 and ∼1.5 eV, respectively. The conduction band offsets are found to be ∼1.7 eV for HfO2 films and ∼0.9 eV for TiO2 films. The high-k HfO2/TiO2 multilayers in p-Si/SiO2/(HfO2/TiO2)/Al2O3/aluminum memory capacitor show a large capacitance-voltage hysteresis memory window of ∼5 V at gate voltage of ±5 V, due to the charge storage in multilayer quantum wells. The hysteresis memory window of ∼1.3 V at small gate voltage of ±1 V is also observed. The high-k HfO2/TiO2 multilayer memory structure can be used in future nanoscale flash memory device applications. [ABSTRACT FROM AUTHOR]

The charge storage characteristics of atomic layer deposited RuOx nanocrystals embedded in high-k HfO2/Al2O3 films in a metal/Al2O3/RuOx/HfO2/SiO2/n-Si structure have been investigated. The size and density of RuOx nanocrystals have been measured using transmission electron microscopy. The RuOx nanocrystals show a density of ∼1×1012/cm2 and a diameter of 5–8 nm. A large hysteresis memory window of ∼13.3 V at a gate voltage of 9 V has been observed for RuOx nanocrystal memory capacitors. A hysteresis memory window of 0.7 V has also been observed under a small sweeping gate voltage of 1 V. A promising memory window of RuOx nanocrystals has been observed as compared with those of pure HfO2 and Al2O3 charge trapping layers, due to charge storage in the RuOx metal nanocrystals. The RuOx nanocrystal memory capacitor has similar leakage current with the pure HfO2 and Al2O3 charge trapping layers. The RuOx memory capacitor has a large breakdown voltage of ∼13.8 V. [ABSTRACT FROM AUTHOR]

The electroluminescence of the light-emitting diodes with five-, ten and 30-fold p-type Ge quantum dots grown on n+ Si substrates is studied. The enhanced integral electroluminescence intensity and blueshift of the 30-fold one at high temperature (>200 K) act contrary to those in five- and ten-fold ones. It is attributed to the emission in the higher-fold quantum dots enabled by the injected electrons diffusing the farther at the higher temperature. Transmission electron microscopy shows that the size of the Ge quantum dots and the Si component in them, both increase with increasing the fold number. Due to the strain-induced intermixing at the high-fold quantum dots, those dots hence have large band gap and result in the intensity increment and blueshift at the high temperature. [ABSTRACT FROM AUTHOR]

Heterojunction phototransistors (HPTs) are requested to have high electrical bandwidth (∼1 GHz) performance for their application of high-speed digital fiber communication. In this letter, a method is disclosed to enhance the speed performance of Si/SiGe-based HPTs, which can overcome the low quantum efficiency drawback (∼0.1 A/W) of Si-based high-speed photodetectors at the wavelength of 850 nm due to its large internal gain. By use of the substrate terminal of HPT, the speed performance can be enhanced greatly with much less reduction in optical gain as compared to the traditional technique with base-terminal-bias. Under proper optical power excitation and the common ground of substrate and emitter terminals, we can achieve 1.8 GHz fast-Fourier-transformed electrical bandwidth with 0.7 A/W responsivity simultaneously. The demonstrated device structure can serve as a key component in the short-reach fiber communication system. [ABSTRACT FROM AUTHOR]

A simple and complementary metal-oxide-semiconductor-compatible method for fabricating germanium (Ge) single-electron transistors (SETs) is proposed, in which the Ge quantum dots (QDs) are naturally formed by selective oxidation of Si0.95Ge0.05/Si wires on a silicon-on-insulator substrate. Clear Coulomb-blockade oscillations, Coulomb staircase, and negative differential conductances were experimentally observed at room temperature. The tunneling currents through the Ge QDs were simulated by the Anderson model with two energy levels. Analysis of the current–voltage characteristics indicates that the single-electron addition energy of the Ge QD is about 125 meV. [ABSTRACT FROM AUTHOR]

Nanorings with an average height and diameter of 1.2 and 65 nm, respectively, were observed to form in Si-capped Ge quantum dots grown at 600 °C by ultrahigh-vacuum chemical vapor deposition. The nanorings were captured with the rapid cooling of the samples with appropriate amount of Si capping. Based on the results of transmission electron microscopy and Raman spectroscopy, the formation of nanorings is attributed to alloying and strain relief in the Si/Ge/(001)Si system. The self-assembly of nanorings provides a useful scheme to form ultrasmall ring-like structure and facilitates the characterization of the physical properties of unconventional quantum structures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A complementary metal-oxide-semiconductor-compatible method is proposed to form atomic-scale germanium (Ge) quantum dots (<10 nm) for application in single-electron devices or optical devices. The formation of Ge quantum dots is realized by the Ge atoms’ segregation and agglomeration during thermal oxidation of Si[sub 1-x]Ge[sub x] alloys. The size and distribution of the Ge dots are determined by conditions of thermal oxidation process and Ge content in the alloys. An average Ge-dot size of 5.1 nm with standard deviation of 1.79 nm and a comparatively uniform spatial distribution (dot density of 7.9×10[sup 11] cm[sup -2]) could be obtained by selective oxidation of Si[sub 0.85]Ge[sub 0.15]/Si-on-insulator structure. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Room-temperature electroluminescence at 1.3 and 1.5 μm from Ge/Si quantum-dot light-emitting diodes is reported. The devices were fabricated in a mesa-type structure, with a silicon oxide layer on the top for surface/sidewall passivation. Different passivation processes were employed. We found that the integrated electroluminescence intensities were relatively less sensitive to temperature, persisting at nearly the same intensity up to RT. The fabricated device shows an internal quantum efficiency of about 0.015% at RT. The improved emission property is attributed to the reduced nonradiative recombination centers due to the surface passivation and thermal treatment. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper investigates the repeatable unipolar/bipolar resistive switching memory characteristics in a copper/germanium-oxide/tungsten (Cu/GeOx/W) structure. The switching mechanism occurs because of the lower barrier height for hole injection rather than electron injection. Therefore, Cu ions, as a positive charge, migrate before initiating growth at the GeOx/W interface and dissolving at the GeOx/Cu interface. The diameter of the Cu nanofilament increases linearly from 0.13 Å to 25 nm as current compliances increase from 1 nA to 10 mA, as calculated using the other approach. The crystalline Cu nanofilament was also confirmed by high-resolution transmission electron microscopy analysis under SET. Good data retention with high resistance ratios of 102-105 (and >104 at 85 °C) and ∼109 was obtained under the bipolar and unipolar modes, respectively. Therefore, a maximum memory size of 5000 Pbit/in2 can be designed in the future. [ABSTRACT FROM AUTHOR]