A high-performance short-wavelength infrared n-i-p photodiode based on InAs/InAs1−xSbx/AlAs1−xSbx type-II superlattices on GaSb substrate has been demonstrated. The device is designed to have a 50% cut-off wavelength of ∼1.8 μm at 300 K. The photodetector exhibited a room-temperature (300 K) peak responsivity of 0.47 A/W at 1.6 μm, corresponding to a quantum efficiency of 37% at zero bias under front-side illumination, without any anti-reflection coating. With an R × A of 285 Ω cm2 and a dark current density of 9.6 × 10−5 A/cm2 under −50 mV applied bias at 300 K, the photodiode exhibited a specific detectivity of 6.45 × 1010 cm Hz1/2/W. At 200 K, the photodiode exhibited a dark current density of 1.3 × 10−8 A/cm2 and a quantum efficiency of 36%, resulting in a detectivity of 5.66 × 1012 cm Hz1/2/W.

The thermal treatment method was employed to prepare nickel-cobalt oxide (NiO/Co₃O₄) nanoparticles. This method was attempted to achieve the higher homogeneity of the final product. Specimens of nickel-cobalt oxide were characterized by various experimental techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). X-ray diffraction results showed that there was no crystallinity in the predecessor, and it still had the amorphous phase. The formations of the crystalline phases of the nickel-cobalt oxide nanoparticles started from 350–500 °C, and the final products had different crystallite sizes ranging from 11–35 nm. Furthermore, the variation of DC conductivity (σ_dc), impedance, tangent loss (tgδ) and dielectric constant (ε′) of the calcined specimens with frequency in the range of 10²–10⁶ Hz was investigated. σ_dc showed a value of 1.9 × 10⁻⁶ S/m, 1.3 × 10⁻⁶ S/m and 1.6 × 10⁻⁶ S/m for the specimens calcined at 350, 400 and 450 °C, respectively. Additionally, a decrease in tgδ values with an increase in temperature was observed. Finally, the formed nanoparticles exhibited ferromagnetic behaviors, which were confirmed by using a vibrating sample magnetometer (VSM).

Moderation of internal quantum mechanical energies, such as exchange energy of an unconventional contact, comprised of a system of 2-D charge carriers, improves performance merits of variable capacitors, varactors, mainly in tuning ratio (TR), and sensitivity, S. Energy transfer from the unconventional contact to the dielectric increases the energy density and enhances the capacitance of the varactor. Here, we analyze the performance of an unconventional varactor based on a planar metal-semiconductor-metal (MSM) structure with an embedded layer of high-density 2-D electron gas (2DEG). Through localized field-assisted manipulation of the 2DEG density, a twice larger equilibrium capacitance and a minimum capacitance, less than the geometric capacitance of a conventional MSM, are achieved. Moreover, the maximum capacitance increases through a Batman-shaped capacitance enhancement at a threshold voltage. Therefore, giant is attained while maintaining quality factors of up to 30. Capacitance-voltage characteristics exhibit a switched-capacitor behavior with S as high as 350 that is due to localized transitions from a dense 2DEG to a complete depletion. This MSM 2-D varactor combines the unconventional features of 2DEG with superior electrical properties of MSMs.

We report on a variable capacitor that is formed between Schottky contacts and the two dimensional electron gas (2DEG) in a planar metal-semiconductor-metal structure. Device capacitance at low bias is twice the series capacitance of anode and cathode, enhancing to a maximum value, Cmax, at a threshold voltage, before reaching a minimum, Cmin, lower than the geometric capacitance of the coplanar contacts, thus resulting in ultra high Cmax/Cmin tuning ratio. Sensitivity, the normalized change of capacitance with voltage, is also very large. The dense reservoir of the 2DEG charge maintained between contacts is shown to be responsible for this remarkable performance.

Analogous to a drop exciting a wave in a reservoir that is detected more rapidly than the drop’s transport by current flow, charge plasma confined in a semiconductor can transfer energy, hence respond much faster than the electric field-induced carrier drift current. Here we construct an optoelectronic device in which charge reservoirs respond to excitation with a speed that is impossible to achieve by transport of charge. In response to short optical pulses, this device produces electrical pulses that are almost 2 orders of magnitude shorter than the same device without the charge reservoirs. In addition to speed, the sensitivity of this process allowed us to measure, at room temperature, as low as 11 000 photons. These micro plasma devices can have a range of applications such as optical communication with a fraction of a microwatt power compared to the present tens of milliwatts, ultrasensitive light detection without cryogenic cooling, photovoltaic devices capable of harvesting dim light, THz radiation detectors, and charged particle detectors.

Capacitance of capacitors in which one or both plates are made of a two-dimensional charge system (2DCS) can be increased beyond their geometric structural value. This anomalous capacitance enhancement (CE) is a consequence of manipulation of quantum mechanical exchange and correlation energies in the ground state energy of the 2DCS. Macroscopically, it occurs at critical charge densities corresponding to transition from an interacting “metallic” to a noninteracting “insulator” mode in the 2-D system. Here, we apply this concept to a metal-semiconductor-metal capacitor with an embedded two-dimensional hole system (2DHS) underneath the plates for realization of a capacitance-based photodetector. Under sufficient illumination, and at critical voltages the device shows a giant CE of 200% and a peak-to-valley ratio of over 4 at probe frequencies larger than 10 kHz. Remarkably, the light-to-dark capacitance ratio due to CE at this critical voltage is well over 40. Transition of the 2DHS from insulator to metallic, enforced by charge density manipulation due to light-generated carriers, accounts for this behavior, which may be used in optical sensing, photo capacitors, and photo transistors.