High performance of AlGaN deep-ultraviolet light emitting diodes due to improved vertical carrier transport by delta-accelerating quantum barriers

Abstract

AlGaN-based deep-ultraviolet light emitting diodes adopting an embedded delta-AlGaN thin layer with an Al composition higher than that in conventional barriers have been investigated. The experimental result shows that when the current is below 250 mA, the maximum of the external quantum efficiency and light output power for the proposed structure reach severally 1.38% and 10.1 mW, which are enhanced significantly by 160% and 197%, respectively, compared to the conventional ones, showing a tremendous improvement. We attribute that to the inserted delta-thin layer's modulation effect on the energy band, namely, accelerating holes to cross the high barrier with very large kinetic energy, thus increasing the hole injection into the active regions. Meanwhile, the electron concentration within the active regions is enhanced as well because of the accompanying additional effect of the delta-AlGaN thin layer being an electron barrier to block electrons escaping from the active region.

Carrier Velocity Modulation by Asymmetrical Concave Quantum Barriers to Improve the Performance of AlGaN-Based Deep Ultraviolet Light Emitting Diodes

“…Both of them are grown on a 1-um-thick annealed AlN buffer layer with a (0001) c-plane sapphire [14], [15], followed by a 0.5-um-thick AlN/AlGaN stress modulation multilayers and a Semiconductor Devices program is adopted in this study to conduct simulations [16], which can help to understand the inherent transport mechanism including the energy band, carrier injection behavior, and carrier distribution within the active region. And the parameter setting can be found in our previous work [9].…”

“…And a multiplicative photoelectric converter on top of the p-type region was promoted to induce the electric-optic conversion, and then multiply the carrier concentration within the active region [8]. Additionally, the structure of active region was also optimized such as the delta-accelerating quantum barriers, which helps holes to accelerate and cross the injection barrier with large kinetic energy [9]. Meanwhile, in the aspect of electron leakage, numerous approaches have been proposed, such as the multiple quantum barrier electron blocking layer (MQB-EBL) [10], [11], Al-composition graded quantum barrier [12], and single-spike quantum barrier [13], to increase the barrier height of quantum barrier or EBL for electrons, thus suppress the electron leakage.…”

Calculating the Effect of AlGaN Dielectric Layers in a Polarization Tunnel Junction on the Performance of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

“…However, it is difficult to achieve highefficiency doping, particularly p-type doping, in AlGaN with a high Al content [10,11]. In addition, AlGaN has much lower hole mobility than electron mobility (electron mobility of ~300 cm 2 /V•s and hole mobility of ~14 cm 2 /V•s at room temperature for unintentionally doped AlN [12,13]), which results in low hole injection efficiency and high electron leakage [5,[14][15][16][17][18][19][20][21][22][23]. Moreover, poor ohmic contact between AlGaN and the electrode will increase the series resistance of an LED.…”

The marvelous optical performance of AlGaN-based deep ultraviolet light-emitting diodes with AlInGaN-based last quantum barrier and step electron blocking layer

“…High threading dislocation density (TDD) and Auger recombination also severely affect the optoelectronic performance of DUV LEDs. Researchers proposed different DUV structures to enhance the optical characteristics and reducing highly TDD using buffer layers or patterned sapphire substrates [ 9 , 11 ], p-doped delta-accelerating [ 12 ], and quaternary-graded quantum barrier [ 13 ]. It is worth noting that electrons have lower effective thermal velocity due to their higher effective mass, so electrons easily overcome the effective potential barrier height (denoted by Φ e ) of quantum barriers and EBL, resulting in leakage to the p-type layers [ 14 ].…”