Fabrication of vertical AlGaN-based deep-ultraviolet light-emitting diodes operating at high current density (∼43 kA cm⁻²) using a laser liftoff method

Abstract

We have successfully fabricated vertical light-emitting devices by separating a 1 × 1 cm2 wafer composed of deep-ultraviolet light-emitting diode (LED) on a sapphire substrate from the substrate using a laser liftoff (LLO) method. Reproducible substrate separation was achieved by the LLO method using an Al0.68Ga0.32N underlayer film on an AlN template with periodic pillars. The fabricated vertical LED successfully demonstrated notable luminescence (peak wavelength: 298 nm) characteristics up to a current density of ~43 kA cm−2 at room temperature and in pulsed drive, which is expected to be used in high-power LEDs and laser diodes.

Centimeter-scale laser lift-off of an AlGaN UVB laser diode structure grown on nano-patterned AlN

“…27) Recently, we demonstrated the high current density operation of the vertical AlGaN UVB LED using the LLO with 257 nm pulsed laser for AlGaN on the nano-patterned AlN. 28) This result evidently indicated this LLO could be realized while maintaining the UVB light-emitting device structure with a high AlN molar fraction on a large area with high yield without the aforementioned dislocation generation.…”

“…On the nano-patterned AlN, unintentionally doped AlGaN (u-AlGaN) and n-AlGaN of a UVB LD structure were grown by MOVPE under the same conditions and with structures similar to that used in a previous study. 9,28) Note that this structure could be realized while maintaining the UVB LD structure with low TDDs, which has already achieved the laser oscillation at RT. 9) Before the LLO, the backside of a one-side-polished sapphire substrate was ground and polished to minimize scattering from the backside of the sapphire substrate.…”

Unexpected Realization of N-Polar AlN Films on Si-Face 4H–SiC Substrates Using RF Sputtering and High-Temperature Annealing

“…Ultra-wide band gap Al-rich AlGaN is one of the most promising materials to build efficient deep ultraviolet light-emitting diodes (DUV LEDs), laser diodes (LDs), and next-generation high electron mobility transistors (HEMTs) with high breakdown voltage. − The polarity of AlGaN affects the performance of related optoelectronic and power devices, and N-polar devices offer theoretically unique advantages over the Al-polar counterparts. For example, N-polar AlGaN DUV LEDs have better carrier injection efficiency and alleviated electron overflow than the Al-polar ones .…”

Increased Light Extraction of Thin-Film Flip-Chip UVB LEDs by Surface Texturing

“…In recent work, this has been improved by growing on nanopatterned AlN and by polishing the surface after the LLO to remove metal residues and surface cracks. This is however challenging to do uniformly on strained wafers with bow. , Alternatively, to circumvent LLO, UVB LEDs have been grown on SiC substrates to allow substrate removal by polishing and dry etching …”

“…This is however challenging to do uniformly on strained wafers with bow. 15,16 Alternatively, to circumvent LLO, UVB LEDs have been grown on SiC substrates to allow substrate removal by polishing and dry etching. 17 Recently, we have shown an alternative method for the substrate removal, namely selective lateral electrochemical etching of AlGaN sacrificial layers 18 and realized a proof-ofconcept TFFC UVB LED.…”