J. Salzman

Fabrication of triangular nanobeam waveguide networks in bulk diamond using single-crystal silicon hard masks

A scalable approach for integrated photonic networks in single-crystal diamond using triangular etching of bulk samples is presented. We describe designs of high quality factor (Q = 2.51 × 106) photonic crystal cavities with low mode volume (Vm = 1.062 × (λ/n)3), which are connected via waveguides supported by suspension structures with predicted transmission loss of only 0.05 dB. We demonstrate the fabrication of these structures using transferred single-crystal silicon hard masks and angular dry etching, yielding photonic crystal cavities in the visible spectrum with measured quality factors in excess of Q = 3 × 103.

Nonvolatile low-voltage memory transistor based on SiO2 tunneling and HfO2 blocking layers with charge storage in Au nanocrystals

We demonstrate a low voltage nonvolatile memory field effect transistor comprising thermal SiO2 tunneling and HfO2 blocking layers as the gate dielectric stack and Au nanocrystals as charge storage nodes. The structure exhibits a memory window of ∼2 V at an applied sweeping voltage of ±3 V which increases to 12.6 at ±12 V. Retention tests show an extrapolated loss of 16% after ten years in the hysteresis width of the threshold voltage. Dynamic program/erase operation reveal an approximately pulse width independent memory for pulse durations of 1 μs to 10 ms; longer pulses increase the memory window while for pulses shorter than 1 μs, the memory windows vanishes. The effective oxide thickness is below 10 nm with very low gate and drain leakage currents.

A nonvolatile memory capacitor based on Au nanocrystals with HfO2 tunneling and blocking layers

We report on a nonvolatile memory capacitor based on gold nanocrystals serving as charge storage elements located between two HfO2 films acting as the tunneling and control layers. The capacitor has an equivalent oxide thicknesses of 7 nm and exhibits a large hysteresis in the C-V characteristics of 1 and 9 V for gate voltage sweeps of ±1 and ±7 V, respectively, with no frequency dependence in the range of 10 kHz to 1 MHz. The storage charge density is ∼1.2×1013 cm−2 and the flat band voltage shift is stable for write/erases operations with a voltage swing of ±5 V for over 18 h.

Thermally activated electrical conductivity in thin GaN epitaxial films

Temperature-dependent Hall measurements of thin GaN films subjected to He ion irradiation at ever increasing doses are used to study the electron transport in GaN. It is shown that electron transport is a thermally activated process with activation energies gradually increasing with reciprocal net carrier concentration, until a saturated value of the activation energy is reached. These experiments provide a direct verification that conductivity in thin GaN layers is controlled by potential barriers caused by depletion of carriers at grain boundaries in the material. Values of average grain size, density of surface states at the grain boundaries, and their energetics are extracted from the experiment.

A Nonvolatile Memory Capacitor Based on a Double Gold Nanocrystal Storing Layer and High-k Dielectric Tunneling and Control Layers

We present a metal-insulator-semiconductor nonvolatile memory capacitor based on two gold nanoparticle charge storage layers, two Hf0 2 layers, and a multilayer HfNO/HfTiO stack. The device exhibits an equivalent oxide thickness of 7.3 nm, a hysteresis of 15 V at a gate voltage of +11 to -8 V, and a storage charge density of 2.75 × 10 13 cm -2 . A leakage of 3.6 × 10- 5 A/cm 2 at -10 V, a breakdown voltage of 13.3 V, and good retention properties with a hysteresis window of 10 V following more than 10 h of consecutive write/erase operations with a ±7 V swing were demonstrated. The capacitor characteristics are frequency-independent in the 10 kHz-1 MHz range.

Enhanced electro‐optic effect in amorphous hydrogenated silicon based waveguides

We report on a direct measurement of the electro‐optic effect in amorphous hydrogenated silicon based waveguides. The observed phase modulation with an applied voltage shows evidence of a threshold voltage below which the electro‐optic effect is weak. At high voltages the electro‐optic phase modulation is nonquadratic and significantly enhanced with respect to the bulk effect in amorphous silicon. These results are explained in terms of a model which considers inhomogeneous electric fields within the silicon layer due to voltage dependent space charges.

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.

Optical properties of nonvolatile memory capacitors based on gold nanoparticles and SiO2–HfO2 sublayers

We describe the effect of optical excitation of state of the art nonvolatile memory capacitors. The devices comprise Au nanocrystals sandwiched between a SiO2 tunneling layer and a HfO2 blocking layer and exhibit an effective oxide thickness of 7.5 nm. The memory properties are modified by the optical excitation due to nonequilibrium depletion. Optical control with different illumination wavelengths as well as variable optical intensities and pulse widths is described.

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.