Dual-band metal–semiconductor–metal (MSM) photodetectors (PDs) with a Ga2O3/MgZnO heterostructure were fabricated by radio frequency (RF) sputtering, which can detect ultraviolet C (UVC) and ultraviolet B (UVB) bands individually by controlling different bias voltages. A PD with the annealing temperature of Ga2O3 at 600 °C can improve the crystal quality of Ga2O3 thin film and exhibit the least persistent photoconductivity (PPC) effect. However, a PD with the annealing temperature of Ga2O3 at 600 °C cannot achieve a voltage-tunable dual-band characteristic. On the contrary, the PD without annealing can suppress the carriers from the bottom layer of MgZnO thin film at a lower bias voltage of 1 V. At this time, the peak responsivity at 250 nm was mainly dominated by the top layer of Ga2O3 thin film. Then, as the bias voltage increased to 5 V, the peak detection wavelength shifted from 250 (UVC) to 320 nm (UVB). In addition, the PD with a 25 nm–thick SiO2 layer inserted between Ga2O3 and MgZnO thin film can achieve a broader operating bias voltage range for dual-band applications.

In this study, GaN-based blue light-emitting diodes (LEDs) with an n-GaN electron transmission layer (ETL) grown between prestrain layer and multiple quantum wells region were fabricated and investigated. As the thickness of ETL increased from 15 to 45 nm, the LEDs generated a 2DEG-like structure with better current spreading ability presented a lower forward voltage of 3.18 V, the light output power (LOP) was improved by 12.5%, and efficiency droop was less than the others. However, as the concentration of ETL increased from 2 × 1018 to 5 × 1018 cm−3, the LEDs performed an obvious decrease in LOP and increase in efficiency droop due to the serious electron overflow. On the other hand, the low temperature electroluminescence and hot/cold factors of LEDs with 45-nm-thick ETL also exhibited better properties, and its hot/cold factor was still quite high (0.87) even at an injection current of 700 mA.

The MgZnO/SiO2/ZnO metal–semiconductor–metal (MSM) dual-band UVA and UVB photodetectors (PDs) with different MgZnO thicknesses were fabricated by RF sputter. From the dark current, it was found that the PD with 200 nm thick MgZnO had a lower leakage current, which implies less defect density and better crystal quality. Therefore, the FWHM of the X-ray diffraction and grain size of the scanning electron microscope image for PDs with a thicker MgZnO thickness were narrower and larger than those of the others. From the photoluminescence (PL) at room temperature, the main defect types of the MgZnO/SiO2/ZnO thin film included Ov, Oi, and Zni. Then, a variable and voltage-controlled tunable wavelength of UV PD from UVB to UVA can be well accomplished by using a SiO2 blocking layer inserted between the MgZnO and ZnO thin film. Therefore, at a lower and higher bias voltage, the PD with a 200 nm thick MgZnO can detect the UVB and UVA range, respectively.

The numerical simulations of blue InGaN/GaN light-emitting diodes (LEDs) with the combined structures of p-GaN/InGaN shortperiod superlattice (SPS) last barrier (LB) and p-AlGaN/GaN SPS electron blocking layer (EBL) are investigated by the Advance Physical Model of Semiconductor Devices (APSYS) program. The simulation results show that the newly designed LEDs get better performances over the original structure of InGaN/GaN LEDs. This is attributed to the enhancement of the hole injection efficiency and the improvement of the polarization field effect between the InGaN well and the GaN barrier layer in the multiple quantum wells (MQWs). Therefore, the simulation results exhibit a significant increment in radiative recombination rate and about 2.6 times enhancement in the internal quantum efficiency (IQE) at an injection current of 150 mA. More important of all, it also shows that the newly designed structure can obviously reduce the ratio of efficiency droop of the LEDs from 62 to 14.5%.The high-brightness InGaN/GaN LEDs are considered to be the most candidates in the applications on liquid crystal display back lighting, automobile headlamps, and solid-state lighting. However, the efficiency droop is still a serious issue for high-power LEDs applications. It is known that this phenomenon with the significantly reduction of the efficiency of LEDs at high current density has been called the "efficiency droop". Regarding the mechanisms of efficiency droop, several possible causes for the efficiency droop include poor carrier confinement, 1 Auger recombination, 2-4 electron leakage, 5-7 and poor hole injection. 8-10 However, the origin of the efficiency droop mechanism for nitride-based LEDs is still a controversial and uncertain issue until now. Among them, the insufficient hole injection efficiency and the electron overflow effect are very important key issues due to the relatively low mobility of the hole compared with the electron and insufficient potential barrier height for the electron in the conduction band for GaN-based materials. The conventional bulk p-AlGaN EBL between the LB and p-GaN layer acted as a potential barrier for the electron in the conduction band can effectively suppress the electron overflow from the MQWs to the p-GaN layer. However, the conventional bulk p-AlGaN EBL also created a potential barrier for the hole in the valence band, which obstructed the hole injected into the active region. 11 Consequently, some studies have had some specific designs of the LB structure to improve the carrier injection and reduce the efficiency droop in the GaN-based LEDs, such as a p-doped LB and a p-doped SPS LB. 12,13 In addition, several different energy band engineering designs on EBL also have been suggested like as: a graded p-AlGaN EBL, a p-AlGaN/GaN SPS EBL, and a triangle shape pAlGaN/GaN/AlGaN EBL. 14-16 The purposes of these designs are the improvement of the hole concentration and the enhancement of the radiative recombination rate in the MQWs.On the other hand, GaN-based materials generally exis...

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