We report on AlGaN/GaN heterostructures ultraviolet (UV) p–i–n photodetectors (PDs) in which generationrecombination and tunneling currents dominate PD leakage at high reverse voltage. At low voltages, the shunt current related to threading dislocations dominate PD leakage. The PD exhibits a narrow bandpass spectral responsivity characteristics from 320 to 360 nm, a zero bias peak responsivity 0.155 A/W at 360 nm, which corresponding to a quantum efficiency of 53%. Additionally, the effect of polarization effect on responsivity of the PD have been investigated.
Organic light-emitting devices (OLEDs) with stable white light emitting were fabricated by using exciton adjusting layer (EAL) inserted between dual emitting layers (EMLs). Three charge transport materials with different characteristics were chosen as EAL, including 4,7-diphenyl-1,1′-phenanthroline (Bphen), N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) and N,N′-dicarbazolyl-3,5-benzene (mCP). Device structure was given as: ITO/NPB (30 nm)/mCP: (t-bt)2Ir(acac) (2 nm, 4 wt.%)/EALs/ mCP: Firpic (12 nm, 10 wt.%)/Bphen (35 nm)/Mg: Ag (100 nm). The results showed that, compared with device without EAL, the devices employed EAL yielded high device performance as well as favorable luminescence property and stable white emission. For the device with mCP EAL, the maximum brightness of 24700cd/m2 and current efficiency of 14.5 cd/A were obtained, while the CIE coordinates of device changed from (0.33, 0.35) to (0.35, 0.36) with the bias voltage increasing from 5 V to 12 V. It was suggested that by incorporating EAL in OLEDs, the charge carrier recombination zone was broadened, and the balance of electron-hole was improved between EMLs.
In this paper, we proposed a p-i-n AlGaN EBL, which is easy to realize in epitaxy, to enhance the electron confinement and improve the hole injection efficiency. The physical and optical properties of GaN-based MQW LEDs with the conventional EBL are also investigated comparatively. The simulation results show that the LEDs with the p-i-n EBL exhibit much higher output power and smaller efficiency droop at high current as compared to those with the traditional EBL due to the enhancement of the electron confinement and improvement of the hole injection from p-type region, which are induced by the strong reverse electrostatic fields in the p-i-n EBL.
GaN ultraviolet (UV) p–i–n photodetectors (PDs) with a thin p-AlGaN/GaN contact layer are designed and fabricated. The PD exhibits a low dark current density of∼7 nA/cm2 under −5 V, and a zero-bias peak responsivity of ∼0.16 A/W at 360 nm, which corresponds to a maximum quantum efficiency of 55%. It is found that, in the wavelength range between 250 and 365 nm, the PD with thin p-AlGaN/GaN contact layer exhibits enhanced quantum efficiency especially in a deep-UV wavelength range, than that of the control PD with conventional thin p-GaN contact layer. The improved quantum efficiency of the PD with thin p-AlGaN/GaN contact layer in the deep-UV wavelength range is mainly attributed to minority carrier reflecting properties of thin p-AlGaN/GaN heterojunction which could reduce the surface recombination loss of photon-generated carriers and improve light current collection efficiency.
GaN-based homojunction p-i-n ultraviolet (UV) photodetectors (PDs) with the conventional structure and delta doped layer in the p-n interface are investigated numerically. Using the delta doped n-type layer, the PDs exhibit much higher responsivity and almost does not affect the dark current as compared to conventional one. Simulation results show that the enhancement of the carrier injection from p-type region, which is the main reason behind the improved performance of GaN-based p-i-n PDs employing the delta doping. This beneficial effect is more remarkable in situations with higher p-cap absorption, such as devices with a thickness p-cap layer or devices with a higher Aluminium composition.
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