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We report a GaN-based Schottky barrier diode with a p-NiO field ring and field plate. It shows a low turn-on voltage (V ON) of ∼0.6 V, an On-resistance (R ON) of ∼6.5 mΩ·cm2, a nearly unity ideality factor of 1.13 at V F = 0.3 V, and a high on/off current ratio of ∼1010. The breakdown voltage (BV) is increased from 300 to 1100 V, rendering a relatively high Baliga’s power figure-of-merit of ∼0.2 GW cmâˆ'2. The improved performance is attributed to the improved current spreading effect and the suppressed field crowding effect via the implemented p-NiO. [ABSTRACT FROM AUTHOR]

GaN-based ultraviolet (UV) detectors have a considerable application potential in many fields. In this Letter, we report an alternative strategy to realize a high-optical-gain bipolar UV phototransistor based solely on a GaN p-i-n epilayer. The device consists of two tightly adjacent vertical p-i-n structures with a common n-type layer as a floating base. The collector and emitter electrodes are deposited on the two p-type mesas, forming a three-dimensional metal–semiconductor–metal (MSM) like photodetector. As a result, a peak responsivity of 11.7 A/W at a wavelength of 358 nm at 5 V is realized, corresponding to an optical gain of 40 with the assumption of 100% internal quantum efficiency. Different from traditional GaN-based n-p-i-n phototransistors, the optical gain of this detector originates from the accumulated electrons in the n-type floating base upon illumination, which can lower the barrier height between the base and emitter, leading to hole emission from the emitter. Although the structure of this phototransistor is similar to a planar back-to-back Schottky-type MSM photodetector, the response speed is much faster because the gain mainly results from carrier emission rather than MS interface defects. [ABSTRACT FROM AUTHOR]

GaN-based micro-size light-emitting diode (μLED) have emerged as a promising light sources for a wide range of applications in displays, visible light communication etc. In parallel with the two key technological bottlenecks: full-color scheme and mass transfer technique that need overcoming, it is known that the low external quantum efficiency (EQE) is also another challenge for μLEDs from the perspective of manufacturing technology and device physics. The low EQE for GaN based μLEDs is opposite to the common belief for GaN-based LEDs, such that GaN based LEDs are featured with high quantum efficiency, mechanically robust and energy saving. Therefore, in this work, we have reviewed the origin for the low EQE for μLEDs. More importantly, we have also reported the underlying devices physics and proposed optimization strategies to boost the EQE for μLEDs. Our work is targeted to provide a guideline for the community to develop high-performance GaN-based μLEDs. [ABSTRACT FROM AUTHOR]

GaN-based vertical cavity surface emitting laser (VCSEL) features the quasi-vertical architecture, and thus a poor lateral current can be encountered, which can significantly reduce the net modal gain and decrease the lasing power. To prevent the holes from lateral leaking outside of the aperture region, we propose GaN based VCSELs with an NP-GaN structure below the buried insulator layer. The reverse biased NP-GaN junction can produce energy barrier that can better suppress the lateral hole leakage outside of the aperture, therefore the better stimulated radiative rate and device lasing power are obtained. Moreover, we also conduct parametric study regarding the impact of different NP-GaN junction designs with various doping concentrations and architectural sizes for the p-GaN layer on the lateral hole confinement capability. [ABSTRACT FROM AUTHOR]

Due to the low hole mobility and the unsatisfying p-type doping efficiency, the p-type layer has a low effective hole concentration and a large electrical resistivity that result in poor hole injection efficiency and significant current crowding effect for III-nitride light-emitting diodes (LEDs). In this work, we report a III-nitride LED architecture comprising a dielectric-constant-controlled tunnel junction to improve both the current spreading effect and the hole injection efficiency. The dielectric-constant-controlled tunnel junction is an n+-GaN/AlGaN/p+-GaN heterojunction, in which the dielectric constant for the AlGaN layer is smaller than that for the GaN layer, and therefore, compared to the conventional n+-GaN/p+-GaN homojunction, the electric field within the tunnel junction is increased and hence, the hole injection can be substantially enhanced if the n+-GaN/AlGaN/p+-GaN heterojunction is properly designed. Furthermore, the proposed device can better spread the current compared to the LED without a tunnel junction. As a result, the internal quantum efficiency has been improved for the LED possessing the dielectric-constant-controlled tunnel junction. [ABSTRACT FROM AUTHOR]

Graphene, with attractive electrical, optical, mechanical and thermal properties, is considered to be an ideal candidate for transparent conductive electrodes (TCEs) in many optoelectronic devices, including III-nitride based devices. However, high contact resistivity ( ρ c ) between graphene and GaN (especially p-GaN) has become a major challenge for graphene TCEs utilization in GaN-based light-emitting diodes (LEDs). Here, we analyzed the graphene/GaN contact junction in detail and reviewed the current research progress for reducing ρ c in graphene TCEs on GaN LEDs, including interface engineering, chemical doping and tunnel junction design. We also analyzed the current diffusion length for a single layer graphene (SLG) and multiple layer graphene (MLG) TCEs. Finally, to improve the fabrication process compatibility and simplicity with paramount reproduction, a method of directly growing graphene films on GaN by chemical vapor deposition (CVD) is proposed. We also give a short analysis on the reliability of graphene TCEs for GaN-based LEDs. It is believed that this is the ultimate solution for graphene TCEs application for GaN-based LEDs and others in general for other opto- and electrical devices. [ABSTRACT FROM AUTHOR]

InGaN/GaN light-emitting diodes (LEDs) make an important class of optoelectronic devices, increasingly used in lighting and displays. Conventional InGaN/GaN LEDs of c-orientation exhibit strong internal polarization fields and suffer from significantly reduced radiative recombination rates. A reduced polarization within the device can improve the optical matrix element, thereby enhancing the optical output power and efficiency. Here, we have demonstrated computationally that the step-doping in the quantum barriers is effective in reducing the polarization-induced fields and lowering the energy barrier for hole transport. Also, we have proven experimentally that such InGaN/GaN LEDs with Si step-doped quantum barriers indeed outperform LEDs with wholly Si-doped barriers and those without doped barriers in terms of output power and external quantum efficiency. The consistency of our numerical simulation and experimental results indicate the effects of Si step-doping in suppressing quantum-confined stark effect and enhancing the hole injection, and is promising in improving the InGaN/GaN LED performance. [ABSTRACT FROM PUBLISHER]