Browsing by Subject "Electron injection"

Now showing 1 - 7 of 7

Open Access
A charge inverter for III-nitride light-emitting diodes
(American Institute of Physics Inc., 2016) Zhang Z.-H.; Zhang, Y.; Bi, W.; Geng, C.; Xu S.; Demir, Hilmi Volkan; Sun, X. W.
In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO2 insulator layer on the p+-GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p+-GaN and SiO2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO2 layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p+-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.
Open Access
A hole modulator for InGaN/GaN light-emitting diodes
(American Institute of Physics, 2015) Zhang, Z-H.; Kyaw, Z.; Liu W.; Ji Y.; Wang, L.; Tan S.T.; Sun, X. W.; Demir, Hilmi Volkan
The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332meV to ∼294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.
Open Access
Improving hole injection efficiency by manipulating the hole transport mechanism through p-type electron blocking layer engineering
(Optical Society of America, 2014) Zhang, Zi-Hui; Ju, Z.; Liu W.; Tan S.T.; Ji Y.; Kyaw, Z.; Zhang X.; Hasanov N.; Sun, X. W.; Demir, Hilmi Volkan
The p-type AlGaN electron blocking layer (EBL) is widely used in InGaN/GaN light-emitting diodes (LEDs) for electron overflow suppression. However, a typical EBL also reduces the hole injection efficiency, because holes have to climb over the energy barrier generated at the p-AlGaN/p-GaN interface before entering the quantum wells. In this work, to address this problem, we report the enhancement of hole injection efficiency by manipulating the hole transport mechanism through insertion of a thin GaN layer of 1 nm into the p-AlGaN EBL and propose an AlGaN/GaN/AlGaN-type EBL outperforming conventional AlGaN EBLs. Here, the position of the inserted thin GaN layer relative to the p-GaN region is found to be the key to enhancing the hole injection efficiency. InGaN/ GaN LEDs with the proposed p-type AlGaN/GaN/AlGaN EBL have demonstrated substantially higher optical output power and external quantum efficiency.
Open Access
On the hole accelerator for III-nitride light-emitting diodes
(American Institute of Physics Inc., 2016) Zhang Z.-H.; Zhang, Y.; Bi, W.; Geng, C.; Xu S.; Demir, Hilmi Volkan; Sun, X. W.
In this work, we systematically conduct parametric studies revealing the sensitivity of the hole injection on the hole accelerator (a hole accelerator is made of the polarization mismatched p-electron blocking layer (EBL)/p-GaN/p-AlxGa1-xN heterojunction) with different designs, including the AlN composition in the p-AlxGa1-xN layer, and the thickness for the p-GaN layer and the p-AlxGa1-xN layer. According to our findings, the energy that the holes obtain does not monotonically increase as the AlN incorporation in the p-AlxGa1-xN layer increases. Meanwhile, with p-GaN layer or p-AlxGa1-xN layer thickening, the energy that the holes gain increases and then reaches a saturation level. Thus, the hole injection efficiency and the device efficiency are very sensitive to the p-EBL/p-GaN/p-AlxGa1-xN design, and the hole accelerator can effectively increase the hole injection if properly designed.
Open Access
Performance enhancement of GaN metal-semiconductor-metal ultraviolet photodetectors by insertion of ultrathin interfacial HfO2 layer
(AVS Science and Technology Society, 2015) Kumar, M.; Tekcan, B.; Okyay, Ali Kemal
The authors demonstrate improved device performance of GaN metal-semiconductor-metal ultraviolet (UV) photodetectors (PDs) by ultrathin HfO2 (UT-HfO2) layer on GaN. The UT-HfO2 interfacial layer is grown by atomic layer deposition. The dark current of the PDs with UT-HfO2 is significantly reduced by more than two orders of magnitude compared to those without HfO2 insertion. The photoresponsivity at 360 nm is as high as 1.42 A/W biased at 5 V. An excellent improvement in the performance of the devices is ascribed to allowed electron injection through UT-HfO2 on GaN interface under UV illumination, resulting in the photocurrent gain with fast response time. © 2015 American Vacuum Society.
Open Access
Quantum dot/light-emitting electrochemical cell hybrid device and mechanism of its operation
(American Chemical Society, 2016) Frohleiks, J.; Wepfer, S.; Kelestemur Y.; Demir, Hilmi Volkan; Bacher, G.; Nannen E.
A new type of light-emitting hybrid device based on colloidal quantum dots (QDs) and an ionic transition metal complex (iTMC) light-emitting electrochemical cell (LEC) is introduced. The developed hybrid devices show light emission from both active layers, which are combined in a stacked geometry. Time-resolved photoluminescence experiments indicate that the emission is controlled by direct charge injection into both the iTMC and the QD layer. The turn-on time (time to reach 1 cd/m2) at constant voltage operation is significantly reduced from 8 min in the case of the reference LEC down to subsecond in the case of the hybrid device. Furthermore, luminance and efficiency of the hybrid device are enhanced compared to reference LEC directly after device turn-on by a factor of 400 and 650, respectively. We attribute these improvements to an increased electron injection efficiency into the iTMC directly after device turn-on. © 2016 American Chemical Society.
Open Access
Super-radiant surface emission from a quasi-cavity hot electron light emitter
(Springer New York LLC, 1999) O'Brien, A.; Balkan, N.; Boland-Thoms, A.; Adams, M.; Bek, A.; Serpengüzel, A.; Aydınlı, A.; Roberts, J.
The Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure (HELLISH-1) device is a novel surface emitter which utilises hot carrier transport parallel to the layers of a Ga1 - xAlxAs p-n junction incorporating a single GaAs quantum well on the n-side of the junction plane. Non-equilibrium electrons are injected into the quantum well via tunnelling from the n-layer. In order to preserve the charge neutrality in the depletion region, the junction undergoes a self-induced internal biasing. As a result the built-in potential on the p-side is reduced and hence the injection of non-equilibrium holes into the quantum well in the active region is enhanced. The work presented here shows that a distributed Bragg reflector grown below the active region of the HELLISH device increases the emitted light intensity by two orders of magnitude and reduces the emission line-width by about a factor of 3 in comparison with the original HELLISH-1 structure. Therefore, the device can be operated as an ultrabright emitter with higher spectral purity.