Ni–Cu Nanoparticles-Embedded Ag-Based Reflector for High-Efficiency Light-Emitting Diodes

We investigated the use of a silver reflector embedded with Ni–Cu nanoparticles to achieve low resistance and high reflectivity in GaN-based flip-chip light-emitting diodes. Compared to a single layer of Ag, the NC-NPs/Ag reflector exhibits a higher light reflectance of ~90% at a wavelength of 450 nm, a lower contact resistance of 4.75 × 10−5 II cm2, and improved thermal stability after annealing at 400°C. The NC-NPs formed after the annealing process prevents agglomeration of the Ag layer, while also reducing the Schottky barrier height between the p-GaN layer and metal reflector. The LED fabricated with a NC-NPs/Ag reflector exhibited a forward-bias voltage of 3.13 V and an improvement in light output power of 36.6% (at 20 mA), when compared with the LED composed of a Ag SL. This result indicates that the NC-NPs/Ag reflector is a promising p-type reflector for high-intensity light-emitting diodes.

Отрицательная дифференциальная проводимость структур на основе оксида лантана

Using e-beam evaporation technique, transparent surface-hydrated lanthanum oxide (OH-La2O3) films with a thickness of 40, 140, and 545 nm were obtained. The electrical and optical characteristics of Al/OH-La2O3/p-Si structures were studied, where aluminum and a silicon substrate with p-type conductivity were used as the upper and lower electrodes, respectively. Negative differential conductivity region in the conductivity–voltage characteristics for the forward bias voltage was found; a possible mechanism of negative differential conductivity is explained by proton transport in hydrogen bonded chains of water molecules at the OH-La2O3 film surface.

Диодные гетероструктуры с ферромагнитным слоем (Ga, Mn)As

The diode p-(Ga,Mn)As/n-InGaAs/n+-GaAs heterostructures, which differ in thickness (from 5 to 50 nm) of a diluted magnetic semiconductor (Ga,Mn)As layer, were fabricated and studied. We found the negative magnetoresistance effect, reaching 6–8% in a 3600 Oe magnetic field. The effect was conserved up to temperatures of 70–80 K and associated with a decrease in charge carrier scattering due to ferromagnetic ordering in the (Ga,Mn)As layer. The dependence of the magnetoresistance on the forward bias voltage is nonmonotonic with the maximum magnetoresistance and its observation voltage range depending on the (Ga,Mn)As layer thickness. The magnetic field dependences of the magnetoresistance have a hysteretic shape due to the influence of tensile stresses in the (Ga,Mn)As layer grown on top of the relaxed InGaAs material on the appearance of the magnetization component, perpendicular to the structure surface.

Chroma Stability of WOLED with High-Voltage

Multilayer chroma stability of white OLEDs was realized with blue dye DPVBi and red dye DCJTB doped as luminescence layer. The blue dye doping concentration was kept at 6%, at the same time the red dye was reduced from 4%, 2%, 1% to 0.5%. The device color coordinates (CIE) were adjusted from (0.58, 0.42) to (0.31, 0.32), achieving the white light emission. A stable white emission for forward bias voltage changes from 6 to 17 V has been achieved. Its maximum luminance was 15030 cd/m2 at 17 V, and the maximum current efficiency was 4.65 cd/A at 9 V. We contributed the main reason of chroma stability to the complete energy transfer from CBP to DCJTB and the incomplete energy transfer between DPVBi and DCJTB by analyzing the spectrum and characteristic of the device so its performance was enhanced.

Mechanism of Carrier Transport in n-Type β-FeSi2/Intrinsic Si/p-Type Si Heterojunctions

Preparation of n-type β-FeSi2/intrinsic Si/p-type Si heterojunctions was accomplished by facing-target direct-current sputtering (FTDCS) and measuring their current-voltage characteristic curves at low temperatures ranging from 300 K down to 50 K. A mechanism of carrier transport in the fabricated heterojunctions was investigated based on thermionic emission theory. According to this theory, the ideality factor was calculated from the slope of the linear part of the forward lnJ-V plot. The ideality factor was 1.12 at 300 K and increased to 1.99 at 225 K. The estimated ideality factor implied that a recombination process was the predominant mechanism of carrier transport. When the temperatures decreased below 225 K, the ideality factor was estimated to be higher than two and parameter A was estimated to be constant. The obtained results implied that the mechanism of carrier transport was governed by a trap-assisted multi-step tunneling process. At high forward bias voltage, the predominant mechanism of carrier transport was changed into a space charge limit current process.

Determination of Band Gap Energy of Semiconductor in Homojunction Structure Devices by Using Customized Microcontroller Based Apparatus

We have successfully developed a customized apparatus based on microcontroller for simple band gap energy (Eg) measurement of semiconductors in homojunction structure devices. The apparatus consisted of a data acquisition system based on microcontroller AVR ATMega 128 and a thermos flask equipped with temperature controller. It permits recording of current-voltage (I-V) and temperature and subsequently sends data to a computer to enable the computer processing of such data. For samples under tested, we used two types of commercial diode, i.e. Silicon (1N4007) and Germanium (1N60). In this measurement, the voltage across the resistor was used to calculate the current while the voltage across the diode gave the forward bias voltage. The temperature of diode was varied from 5°C to 80°C. During each I-V measurement, the temperature of diode was maintained to be constant by employing a proportional-integral-derivative (PID) controller to the heater. Furthermore, by varying the temperature of diode, we could extract the saturation currents under reverse bias across the diode of each I-V measurement. For the two types of diode, it is found that the Eg of silicon is 1.13 ± 0.03 eV, while that of germanium is 0.71 ± 0.03 eV. This result is closed to the Eg value of each diode indicated in the respective datasheet. Therefore, it suggests for applying this apparatus for measuring Eg of semiconductor in most homojunction structure devices.