High‐Power AlGaN‐Based Ultrathin Tunneling Junction Deep Ultraviolet Light‐Emitting Diodes

Abstract

Tunnel junctions (TJs) offer a unique approach to utilizing nonequilibrium tunneling injection of holes and have demonstrated potential applications in ultraviolet (UV) emitters. However, high operating voltage caused by the wide bandgap of the III‐nitrides has impeded the further promotion of TJ. Here, 275 nm n+‐Al0.45Ga0.55N/p+‐Al0.5Ga0.5N ultrathin tunnel junction (UTJ) deep‐UV light‐emitting diodes (LEDs) are developed for minimizing the electrical losses and achieve, to the current knowledge, the lowest operating voltage (5.7 V) at 300 mA reported to date. This study discovers that Mg‐Si co‐doping occurs in the n+‐Al0.45Ga0.55N layer during the growth of n+‐Al0.45Ga0.55N/p+‐Al0.5Ga0.5N UTJ due to the memory and diffusion effect of Mg, which leads to the formation of Ohmic contact between high‐work‐function Ni/Au and Mg‐Si co‐doped n+‐ Al0.45Ga0.55N layer in UTJ. The Zener diode, fluorine resin, and optimally designed glass lens are incorporated into the chip encapsulation to enhance the reliability and optical performance of the device. Furthermore, a high‐efficiency sterilization deep‐UV light source is developed integrated with 120 UTJ deep‐UV LED chips. Complete surface inactivation at a long irradiation distance (20 cm) is achieved within only seconds using the high‐power sterilization deep‐UV light source. These results indicate that UTJ is promising in developing deep UV LEDs and their integrated light sources.

Contact Engineering of III-Nitrides and Metal Schemes toward Efficient Deep-Ultraviolet Light-Emitting Diodes

“…As for Al-rich n-AlGaN, optimizing the epitaxial growth has proven to be effective in reducing its resistivity. − In addition, rational design of the epitaxial structure plays an ineligible role for AlGaN-based devices. , It was reported that a graded n-AlGaN contact layer was utilized to obtain a high electron concentration near the interface and achieve better n-contact . Particularly, tunnel junctions have been widely implemented in III-nitride laser diodes and LEDs, which effectively address the issues of high series resistance and DUV light absorption. , Our group recently proposed a recorded ultrathin tunnel junction DUV LED, achieving a low forward voltage of 5.7 V at 300 mA …”

“…45,46 Our group recently proposed a recorded ultrathin tunnel junction DUV LED, achieving a low forward voltage of 5.7 V at 300 mA. 47 In the mesa definition process, etching damages, resulting from the plasma etching, generally act as deep-level compensation centers in Al-rich n-AlGaN. This increases the Schottky barrier height at the metal-AlGaN interface and raises the difficulty in forming ohmic contact.…”

Refractive Index Engineering as a New Degree of Freedom for Designing High‐Performance AlGaN‐Based Ultraviolet C Light‐Emitting Diodes

“…The low EQEs are directly linked to the inherent material properties of high‐Al‐composition AlGaN, which result in poor internal quantum efficiency (IQE) and poor light extraction efficiency (LEE). [ 1,7 ] The former issue is mainly attributed to high dislocation density, [ 8–10 ] inadequate hole injection, [ 11–13 ] high electron overflow, [ 14 ] and the strong quantum‐confined Stark effect (QCSE) in multiple quantum wells (MQWs). [ 15,16 ] The latter issue primarily arises from significant UV light absorption by the p‐type GaN contact layer, severe light trapping due to strong total internal reflection (TIR), and the unique optical polarization of strong transverse‐magnetic (TM) polarized emission.…”

Planar Compound Eye Lens for Enhanced Light Extraction Efficiency in AlGaN‐Based Deep Ultraviolet LEDs

“…Substantial efforts have been proposed to enhance LEEs of the DUV-LEDs, mainly by reducing absorption of materials and by breaking boundary conditions at the air/dielectric interface to attenuate TIR, such as utilizing p-AlGaN with low absorption, [7][8][9] Micro/nano structured LEDs, [10][11][12][13] patterned sapphire substrate (PSS), [14][15][16][17][18] inclined/rough sidewall, [19][20][21] plasmonic nanoparticles, [22][23][24][25] optimized metallic reflector etc. [26][27][28][29] However, the AlGaN-based deep ultraviolet LEDs still suffer from limited LEE with multiple fabrication steps.…”