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Infrared photodetectors with In(Ga)As quantum dot (QD) active element functioning on interband and intersubband transitions are currently actively investigated, however, the vertical sensors were mostly reported. In the current study, a multilayer InGaAs/GaAs QD photodetector structure allowing the lateral photocurrent detection at normal incidence has been prepared depositing top contact. In order to have a comparison, a heterostructure with only a stack of InGaAs/GaAs wetting layers (WL) has been grown. In-depth photoelectrical characterization shows an effective broad-band photodetection related to the interband transitions between quantum-confined levels in QDs ranging from 1.03 to 1.38 eV (0.9-1.2 ?m) that covers much wider infrared range in comparison to that from WLs (1.27-1.38 eV). Photoluminescence spectroscopy confirms the existence of QD transitions, observed as intense QD emission which peaked at 1.12 eV (~1 ?m) redshifted in comparison to the WL structure. The mechanisms of photoconductivity are modelled and discussed, comparing both the structures. We also show that our QD stack has an order lower contribution from defects compared to similar QD structures investigated before. At the same time, our structures demonstrate appropriate device characteristics at room temperature, such as the wide dynamic range from 10 to 10 ?W cm and a high photoresponsivity up to 20 A W at low excitation intensities over 10-10 ?W cm, while at higher excitation intensities the responsivity is reduced, exhibiting a strong spectral dependence. Thereby, our results show that the grown multilayer InGaAs/GaAs QD heterostructure is of relevant interest for application in lateral QD photodetectors.

Metamorphic InAs/InGaAs quantum dot (QD) structures have been successfully used in optoelectronics as light-emitting and sensing devices. Previous optical and photoelectrical studies showed many benefits such as the shift of the operating range in the infrared and the possibility of engineering their properties via the control of strain. However, photovoltage (PV) kinetic properties of metamorphic QD structures have not been studied yet. PV kinetics in the vertical metamorphic InAs/In0.15Ga0.85As QD and wetting layer (WL) structures compared with conventional pseudomorphic InAs/GaAs QD ones are investigated. A red-shift of the photoresponse from metamorphic QDs in comparison with pseudomorphic QDs was observed, while the PV magnitudes remain similar. Moreover, time-dependent PV measurements reveal faster increase and decay rates in both the metamorphic samples. At the same time, all the structures reveal a non-monotonous kinetics. This kinetics is explained by an unwanted PV component generated in the interface of n+-GaAs buffer to the semi-insulating GaAs substrate, causing a signal opposite to the main PV generated at the top layers of structure. We believe the findings on faster carrier kinetics in metamorphic QDs can be helpful for the development of novel efficient optoelectronic devices. Specifically, the design of metamorphic QD structure is proposed to be improved by: (i) minimizing strain-related defects, (ii) keeping such interface defects far from QDs, (iii) utilizing n+-GaAs substrates.

We investigated the threshold voltage (V TH) shift in p-GaN gate AlGaN/GaN power HEMTs under both forward and reverse gate bias conditions at different temperatures. With increasing forward gate bias, the V TH first positively shifted and then decreased. While at the reverse gate bias, V TH shifts monotonically increased towards the positive direction. Positive V TH shifts were due to electron trapping while its decrease was attributed to the optical pumping by the internal electroluminescence (EL). The EL emission from the p-GaN gate region was captured. A light illumination test was performed to verify the effectiveness of optical pumping.

Most fault location methods depend on the exact extraction of fault transient feature. However, due to the weak grounding current, arc grounding and intermittent problems, it is difficult to extract the fault transient feature. Based on second-order generalized integrator (SOGI), a single-phase-to-ground fault section location method for neutral point ungrounded system is proposed to address this problem in this paper, which avoids the extraction of fault transient feature. Firstly, the fundamental wave phases of zero sequence voltage and zero sequence current are extracted by second-order generalized integrator. Then, the fault position is located based on their phase difference. Finally, the proposed strategy is tested by the simulation data and the field data. The test results show that the method proposed in this paper can accurately locate fault position. Moreover, the phase extraction method based on SOGI is more accurate than traditional Euler method.

An increase in OFF-state leakage current in p-GaN gate AlGaN/GaN high-electron-mobility transistors (HEMTs), induced by ON-state gate bias, was observed and reported in this paper. Higher OFF-state leakage current was observed with higher gate bias voltage and longer bias duration. We propose that the initial increase in OFF-state leakage current and its subsequent decay with time are due to persistent photoconductivity effects in GaN induced by hole injection and electroluminescence during the ON-state gate bias. At room temperature, it took more than 20 s for the increased leakage current to reduce to its equilibrium level in the dark. The related physical mechanisms underlying this phenomenon in the p-GaN gate HEMT structure are also proposed.

The interface band alignment between GaMnAs and organic material was investigated by current transport measurement in hole only devices with GaMnAs/NPB/Al structure. The current density – voltage (J-V) curves were measured and numerical simulations performed on this device structure yielded the hole injection barrier between GaMnAs and NPB to be 0.77 eV. A vacuum level shift at GaMnAs/NPB interface was deduced as 0.54 eV, indicating a dipole layer across the interface. We attributed the vacuum level shift to the charge transfer across the interface.

We studied organic magnetoresistance (OMAR) and magneto-photocurrent (MPC) in ITO/N,N'-di(naphthalene-l-yl)-N,N'-diplienyl-benzidine (NPB)/A1 sandwich devices with NPB thicknesses of 50 nm. Without illumination, no OMAR is observable. While the MPC curves are found to have different line shapes containing a low field and a high field component, depending on excitation photon energy and applied bias. The analysis of experimental results indicate that: (i) the magnetic field effects in NPB is associated with excitonic states, and (ii) the dissociation of singlet excitons is associated to the high field component and triplet-exciton-charge interaction is to the low field component in MPC curves.

The interface formed between the ferromagnetic semiconductor GaMnAs and the organic semiconductor N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'-diamine (NPB) was investigated using current transport measurement and ultraviolet photoemission spectroscopy (UPS). The hole injection barrier at a GaMnAs and NPB interface was measured as 0.77 eV by modelling the measured current density-voltage (J-V) characteristics in a GaMnAs/NPB/Al structured device. The vacuum level shift at a GaMnAs/NPB interface was deduced to be 0.54 eV, indicating that a dipole layer exists at the interface. A UPS study gave a vacuum level shift of 0.53 eV and a band offset between the GaMnAs valence band and the highest occupied molecular orbital of NPB of 0.79 eV, in good agreement with the results of J-V measurements. We attribute the vacuum level shift to charge transfer across the interface.