J. A. Gupta

Gadolinium silicate gate dielectric films with sub-1.5 nm equivalent oxide thickness

GdSixOy gate dielectric films were deposited on Si(001) substrates using ultra-high-vacuum electron-beam evaporation from pressed-powder targets. Transmission electron microscopy showed that the films were amorphous as deposited and remained amorphous when annealed to temperatures up to 900 °C. Capacitance–voltage measurements indicate an equivalent oxide thickness (EOT) of 13.4 A for a film with composition GdSi0.56O2.59 determined by in situ x-ray photoelectron emission spectroscopy. After forming gas annealing at 500 °C the EOT was reduced to 11.0 A, at a physical thickness of 45 A. The same film has a low leakage current of approximately 5.7×10−3 A cm−2 at +1 V, a reduction of 8.7×104 compared to current density estimates of SiO2 films with the same specific capacitance.

Fast lifetime measurements of infrared emitters using a low-jitter superconducting single-photon detector

We use a superconducting single-photon detector with less than 40Hz dark count rate to measure spontaneous emission lifetimes of quantum wells emitting light at wavelengths of 935 and 1245nm. The timing jitter of the measurement system—which includes the detector and all other electronic and optical components—is 68±3ps. We demonstrate how the infrared sensitivity and Gaussian temporal response function of this superconducting detector present clear advantages over conventional detector technologies.

Origin of switching noise in GaAs/AlxGa1-xAs lateral gated devices

We have studied switching (telegraph) noise at low temperature in

Femtosecond (191 fs) NaY(WO4)2 Tm,Ho-codoped laser at 2060 nm.

\mathrm{Ga}\mathrm{As}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}

Broadly tunable femtosecond mode-locking in a Tm:KYW laser near 2 μm

heterostructures with lateral gates and introduced a model for its origin, which explains why noise can be suppressed by cooling samples with a positive bias on the gates. The noise was measured by monitoring the conductance fluctuations around

Femtosecond mode-locked Tm 3+ and Tm 3+ -Ho 3+ doped 2 μm glass lasers

{e}^{2}∕h

Intersubband transitions in InGaNAs/GaAs quantum wells

on the first step of a quantum point contact at around

Passive mode locking of a Tm,Ho:KY(WO4)2 laser around 2 μm

1.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Single-mode 2.4 μm InGaAsSb/AlGaAsSb distributed feedback lasers for gas sensing

. Cooling with a positive bias on the gates dramatically reduces this noise, while an asymmetric bias exacerbates it. Our model is that the noise originates from a leakage current of electrons that tunnel through the Schottky barrier under the gate into the conduction band and become trapped near the active region of the device. The key to reducing noise is to keep the barrier opaque under experimental conditions. Cooling with a positive bias on the gates reduces the density of ionized donors. This builds in an effective negative gate voltage so that a smaller negative bias is needed to reach the desired operating point. This suppresses tunneling from the gate and hence the noise. The reduction in the density of ionized donors also strengthens the barrier to tunneling at a given applied voltage. Further support for the model comes from our direct observation of the leakage current into a closed quantum dot, around

Electron energy loss spectroscopy of interfacial layer formation in Gd2O3 films deposited directly on Si(001)

{10}^{\ensuremath{-}20}\phantom{\rule{0.3em}{0ex}}\mathrm{A}