Boosted ultraviolet electroluminescence of InGaN/AlGaN quantum structures grown on high-index contrast patterned sapphire with silica array

In this work, we demonstrate a high-performance ultraviolet phototransistor (UVPT) based on the AlGaN/GaN high-electron mobility transistor (HEMT) configuration. When the device is biased at off state, the peak photoresponsivity (R) of 3.6 × 107 A/W under 265 nm illumination and 1.0 × 106 A/W under 365 nm illumination can be obtained. Those two R values are one of the highest among the reported UVPTs at the same detection wavelength under off-state conditions. In addition, we investigate the gate-bias (VGS) dependent photoresponse of the fabricated device with the assistance of band structure analysis. It was found that a more negative VGS can significantly reduce the rise/decay time for 265 nm detection, especially under weak illumination. This can be attributed to a largely enhanced electric field in the absorptive AlGaN barrier that pushes the photo-generated carriers rapidly into the GaN channel. In contrast, the VGS has little impact on the switching time for 365 nm photodetection, since the GaN channel has a larger absorption depth and the entire UVPT simply acts as a photoconductive-type device. In short, the proposed AlGaN/GaN HEMT structure with the superior photodetection performance paves the way for the development of next generation UVPTs.

Demonstration of AlGaN/GaN-based ultraviolet phototransistor with a record high responsivity over 3.6 × 107 A/W

A high responsivity and controllable recovery ultraviolet (UV) photodetector based on a tungsten oxide (WO3) gate AlGaN/GaN heterostructure with an integrated micro-heater is reported for the first time. The WO3 nanolayer was deposited by physical vapor deposition (PVD) for deep UV absorption and the micro-heater was integrated for chip level heating and cooling. Our device when exposed to UV wavelength exhibits a high responsivity of 1.67 × 104 A W−1 at 240 nm and a sharp cut-off wavelength of 275 nm. More importantly, the persistent photoconductivity (PPC) effect can be eliminated by a novel method, mono-pulse heating reset (MHR), which consists in applying an appropriate pulse voltage to the micro-heater right after the removal of the UV illumination. The recovery time was reduced from hours to just seconds without reducing the high responsivity and stability of the photodetector. The UV detection, high responsivity, high stability, controllable recovery process and low production cost of GaN-based photodetectors make these devices extremely attractive for several applications, such as fire detection and missile and rocket warning.

/pdf/a-high-responsivity-and-controllable-recovery-ultraviolet-ktnnyory22.pdf

A high responsivity and controllable recovery ultraviolet detector based on a WO 3 gate AlGaN/GaN heterostructure with an integrated micro-heater

The collective oscillation of electrons located in the conduction band of metal nanostructures being still energized, with the energy up to the bulk plasmon frequency, are called nonequilibrium hot electrons. It can lead to the state-filling effect in the energy band of the neighboring semiconductor. Here, we report on the incandescent-type light source composed of Au nanorods decorated with single Ga-doped ZnO microwire (AuNRs@ZnO:Ga MW). Benefiting from Au nanorods with controlled aspect ratio, wavelength-tunable incandescent-type lighting was achieved, with the dominating emission peaks tuning from visible to near-infrared spectral regions. The intrinsic mechanism was found that tunable nonequilibrium distribution of hot electrons in ZnO:Ga MW, injected from Au nanorods, can be responsible for the tuning emission features. Apart from the modification over the composition, bandgap engineering, doping level, etc., the realization of electrically driving the generation and injection of nonequilibrium hot electrons from single ZnO:Ga MW with Au nanostructure coating may provide a promising platform to construct electronics and optoelectronics devices, such as electric spasers and hot-carrier-induced tunneling diodes.

/pdf/nonequilibrium-hot-electron-induced-wavelength-tunable-1t7fwxk42i.pdf

Nonequilibrium hot-electron-induced wavelength-tunable incandescent-type light sources

In this letter, we report the first demonstration of monolithically integrated ultraviolet (UV) light emitting diodes (LEDs) and visible-blind UV photodetectors (PDs) employing the same p-GaN/AlGaN/GaN epi-structures grown on Si. Due to the radiative recombination of holes from the p-GaN layer with electrons from the 2-D electron gas (2DEG) accumulating at the AlGaN/GaN heterointerface, the forward biased LED with p-GaN/AlGaN/GaN junction exhibits uniform light emission at 360 nm. Facilitated by the high-mobility 2DEG channel governed by a p-GaN optical gate, the visible-blind phototransistor-type PDs show a low dark current of ∼10-7 mA/mm and a high responsivity of 3.5×105 A/W. Consequently, high-sensitivity photo response with a large photo-to-dark current ratio of over 106 and a response time less than 0.5 s is achieved in the PD under the UV illumination from the on-chip adjacent LED. The demonstrated simple integration scheme of high-performance UV PDs and LEDs shows great potential for various applications such as compact opto-isolators.

Monolithic integration of ultraviolet light emitting diodes and photodetectors on a p-GaN/AlGaN/GaN/Si platform.

In this work, a GaN p-i-n diode based on Mg ion implantation for visible-blind UV detection is demonstrated With an optimized implantation and annealing process, a p-GaN layer and corresponding GaN p-i-n photodiode are achieved via Mg implantation As revealed in the UV detection characterizations, these diodes exhibit a sharp wavelength cutoff at 365 nm, high UV/visible rejection ratio of 12×104, and high photoresponsivity of 035 A/W, and are proved to be comparable with commercially available GaN p-n photodiodes Additionally, a localized states-related gain mechanism is systematically investigated, and a relevant physics model of electric-field-assisted photocarrier hopping is proposed The demonstrated Mg ion-implantation-based approach is believed to be an applicable and CMOS-process-compatible technology for GaN-based p-i-n photodiodes

Magnesium ion-implantation-based gallium nitride p-i-n photodiode for visible-blind ultraviolet detection

4H-SiC single photon counting avalanche photodiodes (SPADs) are prior devices for weak ultraviolet (UV) signal detection with the advantages of small size, low leakage current, high avalanche multiplication gain, and high quantum efficiency, which benefit from the large bandgap energy, high carrier drift velocity and excellent physical stability of 4H-SiC semiconductor material. UV detectors are widely used in many key applications, such as missile plume detection, corona discharge, UV astronomy, and biological and chemical agent detection. In this paper, we will describe basic concepts and review recent results on device design, process development, and basic characterizations of 4H-SiC avalanche photodiodes. Several promising device structures and uniformity of avalanche multiplication are discussed, which are important for achieving high performance of 4H-SiC UV SPADs.

Recent progress of SiC UV single photon counting avalanche photodiodes

In this work, the after-pulse properties of 4H-SiC ultraviolet (UV) avalanche photodiodes (APDs) working in gated quenching mode are firstly characterized by using a double gate method. The after-pulse probability is determined as a function of delay time at various overbias voltages and temperatures. It is found that the after-pulse probability of 4H-SiC APDs would decrease at higher chip temperature, supporting the carrier trapping/releasing mechanism. Compared to state-of-the-art Geiger-mode Si APDs, the 4H-SiC APD exhibits considerably larger after-pulsing effect, which should be mainly caused by high density point defects within the SiC epilayer. The maximum signal repetition rate of the SiC APD in gated quenching operation mode is estimated, which is a key performance parameter for future UV laser radar and quantum communication applications.

After-Pulse Characterizations of Geiger-Mode 4H-SiC Avalanche Photodiodes

4H-SiC avalanche photodiodes (APDs) working in Geiger mode are promising devices for ultra-weak ultraviolet light detection. In this letter, the degree of avalanche uniformity across device mesa of 4H-SiC p-i-n APDs is studied by imaging hot carrier luminescence pattern of the devices in avalanche regime. It is found that the luminescence emission from the APD under avalanche always first appears in the [ $\overline 1 \overline 1 20$ ] side of the top contact electrode. As over-bias increases, the luminescence pattern gradually extends toward the [ $11\overline 2 0$ ] direction and finally covers the whole device mesa. A physical model is proposed to explain the non-uniform avalanche phenomenon, in which the substrate off-orientation related carrier lateral drift would cause asymmetric hole accumulation and screening of junction electrical field along the [ $11\overline 2 0$ ] direction.

Spatial Non-Uniform Hot Carrier Luminescence From 4H-SiC p-i-n Avalanche Photodiodes

Optical crosstalk is one of major problems limiting the performance of focal plane arrays based on single photon avalanche diodes (SPADs). In this work, for the first time the crosstalk characteristics of a 4H-SiC SPAD linear array are studied, which is based on a real-time dual channel data acquisition method. It is found that SiC SPAD array exhibits similar crosstalk probability compared with those of InGaAs-based SPAD arrays, which can be effectively reduced by trench isolation between adjacent pixels or by lowering overbias. The average time required for forming a crosstalk event is determined between 7 and 10 ns. As a result, active time-gated operation scheme can be applied for reducing crosstalk.

/pdf/crosstalk-analysis-of-sic-ultraviolet-single-photon-2q1ngf7ehe.pdf

Linlin Su

Papers

Magnesium ion-implantation-based gallium nitride p-i-n photodiode for visible-blind ultraviolet detection

Recent progress of SiC UV single photon counting avalanche photodiodes

After-Pulse Characterizations of Geiger-Mode 4H-SiC Avalanche Photodiodes

Spatial Non-Uniform Hot Carrier Luminescence From 4H-SiC p-i-n Avalanche Photodiodes

Crosstalk Analysis of SiC Ultraviolet Single Photon Avalanche Photodiode Arrays