scholarly journals Response to “Comment on ‘Forward current propagation beyond the virtual cathode formed by a high injection current’ ” [Appl. Phys. Lett. 81, 1530 (2002)]

2002 ◽  
Vol 81 (8) ◽  
pp. 1532-1533 ◽  
Author(s):  
Han S. Uhm ◽  
Eun H. Choi ◽  
Myung C. Choi
Keyword(s):  
Virtual Cathode ◽  
Injection Current ◽  
Forward Current ◽  
High Injection

Forward current propagation beyond the virtual cathode formed by a high injection current

2001 ◽  
Vol 79 (7) ◽  
pp. 913-915 ◽  
Author(s):  
Han S. Uhm ◽  
Eun H. Choi ◽  
Myung C. Choi
Keyword(s):  
Virtual Cathode ◽  
Injection Current ◽  
Forward Current ◽  
High Injection

Approaches Towards the Ultimate Luminous Output Power of Light-Emitting Diodes: Bottlenecks and Remedies

2015 ◽  
Author(s):  
Xiaokun Zhang ◽  
Xiao-Dong Xiang ◽  
Yong Xiang
Keyword(s):  
Output Power ◽  
Light Emitting Diodes ◽  
Thermal Runaway ◽  
Efficiency Droop ◽  
Injection Current ◽  
Light Emitting ◽  
Excessive Heat ◽  
High Injection ◽  
Current Densities ◽  
The Cost

Although light-emitting diodes (LEDs) hold great promises for high-efficiency lighting applications, the cost per lumen still poses a challenge for LEDs to fast penetrate into the markets. Increasing the output power per LED chip reduces the number of chips required for a specific luminous flux, thus reducing the cost of LED luminaires. However, it is well known that the luminous output power of LEDs (Pout) cannot be enhanced simply by increasing the injection current density (Jinj) due to efficiency droop. Extensive efforts have been made towards avoiding efficiency droop at high injection current densities (e.g., Jinj > 50 A/cm2). Gardner et al. reported a double-heterostructure LED with an external quantum efficiency (EQE) of 40% at 200 A/cm2. Xie et al. introduced an electron-blocking layer into the LED devices and the EQE peak occurred at 900 A/cm2 approximately. Nevertheless, the EQE is always lower than 100%, excessive heat will accumulate in LEDs at high current densities and increase the junction temperatures, which will damage the device and limit its luminous output power and lifetime. In this paper, the recombination mechanism in the LED active area is analyzed and an analytic relationship between Pout and Jinj is proposed. The calculated results show that the best Pout currently achieved is far lower than its potential value. The temperature dependence of the Pout-Jinj relationship is also calculated and the thermal state of LEDs at high injection current densities predicted. The results demonstrate that LED luminaires with thermal management based on conventional fin-shaped heat sinks suffer from thermal runaway due to excessive heat accumulation before reaching their ultimate output power. The gap between the existing and predicted Pout is mainly due to thermal runaway of LED devices at high injection current densities, instead of efficiency droop. Therefore, the short-term solution of LED luminous output power enhancement should be better cooling of LED modules, such as jet/spray cooling, heat pipe cooling, or 3D embedded two-phase cooling. Long-term solutions continue to focus on reducing the efficiency droop with improved LED device structures and advanced materials.

High Current Injection to a UV-LED grown on a Bulk AlN Substrate

2003 ◽  
Vol 798 ◽  
Author(s):  
Toshio Nishida ◽  
Tomoyuki Ban ◽  
Hisao Saito ◽  
Toshiki Makimoto
Keyword(s):  
Thermal Conductivity ◽  
Heat Dissipation ◽  
Light Emitting Diode ◽  
Peak Shift ◽  
Emission Peak ◽  
Injection Current ◽  
High Thermal Conductivity ◽  
Uv Led ◽  
High Injection ◽  
Large Injection

ABSTRACTWe applied a bulk AlN substrate to an AlGaN-based ultraviolet light emitting diode (UV-LED) and found that this combination enables high injection current, which shows the LED's potential for large ultraviolet flux extraction. Heat dissipation is an important issue for LEDs. Bulk AlN substrate has high thermal conductivity, a wurtzite crystal symmetry the same as that of nitride emitters, and transparency in the ultraviolet wavelength range. An UV-LED grown on a bulk AlN substrate shows output power linearity up to high injection current up to 300 mA, whereas a similar device grown on an AlN-template formed on a sapphire substrate only shows linearity up to an injection current of about 150 mA. It also showed very stable emission peak wavelength. For example, the emission peak shift is less than 2 nm in spite of the large injection current of 200 mA. Both findings are attributed to the heat dissipation afforded by the high thermal conductivity of the bulk AlN. This LED still suffers from internal absorption loss caused by the residual color centers in the AlN at present. However, further improvement of bulk AlN substrates will lead to high flux and highly efficient ultraviolet sources.

scholarly journals Point Normal Metal-Superconductor (NS) Contact in Nonballistic Regime

2003 ◽  
Vol 17 (10n12) ◽  
pp. 649-656 ◽  
Author(s):  
I. N. Askerzade ◽  
I. O. Kulik
Keyword(s):  
Current Density ◽  
Andreev Reflection ◽  
Injection Current ◽  
Normal Metal ◽  
Excess Current ◽  
High Injection ◽  
Contact Conductivity ◽  
Injection Current Density

We analyze the point NS contact conductivity taking into account the depression of superconductivity at high-injection current density and Andreev reflection at the adaptive NS boundary. The dependence of the excess current on the voltage, as well as conductivity of contact at arbitrary voltage is obtained.

scholarly journals Enhancement in external quantum efficiency of AlGaInP red μ-LED using chemical solution treatment process

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Byung Oh Jung ◽  
Wonyong Lee ◽  
Jeomoh Kim ◽  
Myungshin Choi ◽  
Hui-Youn Shin ◽  
...  
Keyword(s):  
Chemical Treatment ◽  
Solution Treatment ◽  
Surface Recombination ◽  
Injection Current ◽  
Plasma Damage ◽  
Light Emitting ◽  
Chemical Surface ◽  
High Injection ◽  
Transmission Electron ◽  
Sidewall Surface

AbstractTo investigate the effects of their surface recovery and optical properties, extremely small sized (12 µm × 12 µm mesa area) red AlGaInP micro light emitting diodes ($$\upmu$$ μ LED) were fabricated using a diluted hydrofluoric acid (HF) surface etch treatment. After the chemical treatment, the external quantum efficiencies (EQEs) of $$\upmu$$ μ -LED at low and high injection current regions have been improved by 35.48% and 12.86%, respectively. The different phenomena of EQEs have a complex relationship between the suppression of non-radiative recombination originating from the etching damage of the surface and the improvement of light extraction of the sidewalls. The constant enhancement of EQE at a high injection current it is attributed to the expansion of the active region’s sidewall surface area by the selective etching of AlInP layers. The improved EQE at a low injection current is related to the minimization of the surface recombination caused by plasma damage from the surface. High-resolution transmission electron microscopy (HR-TEM) revealed physical defects on the sidewall surface, such as plasma-induced lattice disorder and impurity contamination damage, were eliminated using chemical treatment. This study suggests that chemical surface treatment using diluted HF acid can be an effective method for enhancing the $$\upmu$$ μ -LED performance.

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