GaN/AlGaN high electron mobility transistors (HEMTs) are important devices due to their high-frequency and high-power applications. The two-dimensional (2D) electron density in AlGaN/GaN heterostructures is essential for the design of the state-of-the-art HEMTs. Here, the electro-absorption of GaN/AlGaN HEMTs was investigated using photoluminescence excitation (PLE), which is a sensitive and noncontact optical technique. The built-in electric fields of the GaN and AlGaN layers in HEMTs were derived from the Stark effect in PLE. According to the discontinuity in the displacement electric fields, the 2D electron density in the heterostructures can be estimated from PLE, which agrees with the values obtained from the Hall-effect measurements.

Si δ -doped AlGaAs/InGaAs/AlGaAs quantum well (QW) structure is commonly adopted as one of the core elements in modern electric and optoelectronic devices. Here, the time dependent photoconductivity spectra along the active InGaAs QW channel in a dual and symmetric Si δ -doped AlGaAs/InGaAs/AlGaAs QW structure are systematically studied under various temperatures ( T = 80–300 K) and various incident photon energies ( E _in = 1.10–1.88 eV) and intensities. In addition to positive photoconductivity, negative photoconductivity (NPC) was observed and attributed to two origins. For T = 180–240 K with E _in = 1.51–1.61 eV, the trapping of the photo-excited electrons by the interface states located inside the conduction band of InGaAs QW layer is one of the origins for NPC curves. For T = 80–120 K with E _in = 1.10–1.63 eV, the photoexcitation of the excess ‘supersaturated’ electrons within the active InGaAs QW caused by the short cooling process is another origin.

Resistive switching (RS) and negative differential resistance (NDR) within the same device have promising applications in switches, memory devices, and analog-to-digital converters. In this study, we synthesized molybdenum disulfide (MoS _₂ ) quantum dots (QDs) functionalized with glutathione (GSH) and investigated their electrical properties. Current–voltage ( I – V ) measurements of the QD device revealed the coexistence of RS and NDR at room temperature. By adjusting the voltage scan rate, the NDR effect was enhanced, achieving a peak-to-valley ratio of 23.6. A model based on carrier tunneling and trapping was proposed to explain the observed NDR and RS. Moreover, the device demonstrated excellent durability, maintaining a stable high on/off resistance ratio of approximately 10 ⁴ after 100 voltage-sweep cycles under ambient conditions. These results indicate that GSH-functionalized MoS _₂ QDs exhibit controllable RS and NDR, demonstrating significant potential for advanced multifunctional memory devices.

We investigated the electric noise characteristics of Hall devices made with dual δ -doped InGaAs quantum wells by varying the doping concentration and location. The noise was studied in the frequency range from 0.1 Hz to 1 kHz at room temperature in a transverse configuration, with an active area of 140 × 140 μ m 2 . The Hooge parameter was found to be inversely proportional to the square of the carrier concentration, but independent of the doping location. Such significant reduction of noise, in comparison to the Hooge formula, was explained by the screening of potential modulation provided by the dual δ -doped layers. The results indicate the beneficial role of high carrier concentration in such type of device.

Nanosized ultrathin magnetic films were prepared by controlling the deposition of Fe onto an oxidized NiAl(001) surface with an alumina nanostructure on it. Because the ultrathin ferromagnetic Fe films on the bare NiAl(001) surface are separated by paramagnetic Fe nanoparticles on the alumina stripes, as determined by scanning electron microscopy with spin analysis, they form rectangular domains with sizes ranging from tens of nanometer to larger than a micrometer. Magnetic domain patterning can thus be achieved by controlling the Fe coverage and nanostructured template.