With increasing demands in all-optical signal processing functions such as switching and modulating in integrated photonic-electronic circuits, plasmonic modulators are getting lots of attentions. In this paper, we present a novel design of hybrid plasmonic modulator based on insulator-metal phase transition in vanadium dioxide (VO2). The device consists of two silicon tapers and a metal-VO2-insulator-silicon hybrid plasmonic structure that are inserted into a strip silicon waveguide, with 120 nm x 800 nm modulating section within 450 nm x 2 μm device footprint. By taking advantages of the large refractive index contrast between the metal and semiconductor phase of VO2, the proposed modulator achieves a high modulation depth of 14.852 dB with a low insertion loss of 1.804 dB. Moreover, we have systematically analyzed the geometry dependence of the device and the influence of broadband light on modulation performances. Considering the effects of seed layer in VO2 deposition process, we have also studied the modulating performances using different dielectric layers. Our design can be practically fabricated, and a complete process flow is provided. We believe this work has great values in promoting the industrial process of silicon photonics in the fields of optical communication and data storage.
Waveguide-coupled germanium (Ge) p-i-n photodetectors (PDs) have attracted much attention and have been investigated widely due to their high performance and enable on-chip integration. Conventional waveguide-coupled Ge PDs requires metal contact on Ge as well as doping in Ge to form the p-i-n junction. However, in these devices, the light absorption of metal contacts on Ge leads to a sharp decrease in responsivity. In addition, in the standard CMOS foundries, the technology of forming metal contact with Ge is immature. In this paper, we report on the design, fabrication, and experimental demonstration of an integrated lateral waveguide p-i-n photodetector (PD). We experimentally obtained at a reverse voltage of 3V a dark current of 11 nA, a responsivity higher than 0.73 A/W at 1550 nm wavelength, and a -3 dB opto-electrical cut-off frequency over 66 GHz. The combined benefits of decreased process complexity and high-performance device operation pave the way towards attractive integration strategies to deploy costeffective photonic transceivers on silicon-on-insulator substrates.
Waveguide-coupled germanium (Ge) p-i-n photodetectors (PDs) have attracted much attention and have been investigated widely due to their high performance and enable on-chip integration. In this paper, we report on the fabrication and experimental demonstration of an integrated lateral waveguide p-i-n PD with additional Si doping. In order to achieve a high performance detector, we used a novel silicon substrate doping to improve the electric field intensity in the active region. It is demonstrated by experiment that the strategy using additional Si doping to decrease dark current and to increase the bandwidth is more favorable. Using the additional Si doped p-i-n junction, the waveguide coupled Ge-on-Si p-i-n PD shows a comprehensive performance improvement. With comparison to the conventional waveguide coupled Ge-on-Si p-i-n PD, such a PD, owns an about 60% improvement on the tested -3 dB opto-electrical cut-off frequency and shows the smaller dark current at voltage of -1 V. We obtained at a reverse voltage of 1V a dark current lower than 30 nA, a responsivity higher than 1.1 A/W at 1550 nm wavelength, and a -3 dB optoelectrical cut-off frequency over 25 GHz. Evidently, the waveguide coupled Ge-on-Si p-i-n PD with additional p-i-n junction is very effective to promote the performance of device, which is very promising to be applied in the further high power Ge-on-Si PD fabrication.
In this paper, we present the design and characterization of a novel GaN based ultraviolet (UV) detector. The detector consists of two GaN PIN diodes, connected in antiparallel configuration. Two layers of AlGaN, a 100 nm Al0.4Ga0.6N barrier layer and a 400 nm Al0.33Ga0.67N filter layer are deposited on top of one of the PIN diodes. The filter layer exhibits strong absorption of photons at about 310 nm and below. The barrier layer improves the short wave rejection ratio as it can prevent the diffusion of the carriers generated in the filter layer. Due to the antiparallel connection of the two diodes, the cutoff wavelength of the detector is 300 nm and the overall photocurrent of the detector provides good similarity to the Erythemal action spectrum.
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.
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.
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.
A unique design method of two cascaded diffractive optical elements (DOEs) with different sizes of effective phase region to modulate broadband beam is presented with consideration of single production material and low relief height on DOE. The iterative algorithm to calculate the relief heights on these DOEs is introduced at first. Where after, a broadband beam at wavelength from 500nm to 600nm propagates through the designed DOEs and is focused on the target plane in the simulation part. The shaping results demonstrate the excellent shaping ability of this unique design method. The shaping system proposed in this paper is significant for nonmonochromatic light modulation and has many applications such as graphic encryption, three-dimensional color display and multi wavelength division multiplexing.
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.
This paper presents the comparative analysis of influence of doping level and doping profile of the active region on zero bias photoresponse characteristics of GaN-based p-i-n ultraviolet (UV) photodetectors operating at front- and back-illuminated. A two dimensional physically-based computer simulation of GaN-based p-i-n UV photodetectors is presented. We implemented GaN material properties and physical models taken from the literature. It is shown that absorption layer doping profile has notable impacts on the photoresponse of the device. Especially, the effect of doping concentration and distribution of the absorption layer on photoresponse is discussed in detail. In the case of front illumination, comparative to uniform n-type doping, the device with n-type Gaussian doping profiles at absorption layer has higher responsivity. Comparative to front illumination, back illuminated detector with p-type doping profiles at absorption layer has higher maximum photoresponse, while the Gaussian doping profiles have a weaker ability to enhance the device responsivity. It is demonstrated that electric field distribution, mobility degradation, and recombinations are jointly responsible for the variance of photoresponse. Our work enriches the understanding and utilization of GaN based p-i-n UV photodetectors.
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