BAlGaN alloys nearly lattice-matched to AlN for efficient UV LEDs

Abstract

The lattice mismatch between AlGaN and AlN substrates limits the design and efficiency of UV LEDs, but it can be mitigated by the co-incorporation of boron. We employ hybrid density functional theory to investigate the thermodynamic, structural, and electronic properties of BAlGaN alloys. We show that BAlGaN can lattice match AlN with band gaps that match AlGaN of the same gallium content. We predict that BAlGaN emits transverse-electric polarized for gallium content of ~45% or more. Our results indicate that BAlGaN alloys are promising materials for higher efficiency UV optoelectronic devices on bulk AlN substrates. Main TextThe efficient generation of UV light is useful in many technological applications, including sensing and measurement of inks and markers, protein analysis and DNA sequencing, UV curing of resins and solvent-free printer ink, and, most importantly, disinfection and sterilization. 1,2) AlGaN-based LEDs are the most promising semiconducting UV generation technology due to their wide emission spectrum range (from 6.2 eV for AlN to 3.4 eV for GaN), relatively high-efficiency emission of light, ability to be doped n-and p-type, robust mechanical properties, and lack of toxic elements. 2) Current UV generation technology uses mercury-based lamps, 3) but the Minamata Convention on Mercury 4) has over 100 nations pledged to phase out mercury-based technologies.However, the efficiency of AlGaN-based UV LEDs is still hampered by multiple material issues. Of note, light extraction becomes less efficient for high Al-content LEDs, as the polarization of emitted light switches from transverse electric (TE) (emitted preferentially along the c direction) to transverse magnetic (TM) polarization (emitted preferentially within the c-plane) above 68% Al for 3 nm Al x Ga 1-x N quantum wells. 5,6)

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

“…[ 51 ] In recent proposals for high‐efficiency UVC LEDs, the BAlGaN alloy has been suggested as a promising material for the active region. [ 52 ] The incorporation of boron in BAlGaN can mitigate the QCSE by reducing the built‐in internal polarization field. [ 26 ] The BAlGaN MQWs may also be a favorable candidate for minimizing the refractive index contrast at the heterointerface of MQWs/n‐AlGaN due to the reduced refractive index resulting from boron incorporation.…”

Dawn of nitride ferroelectric semiconductors: from materials to devices

“…Boron-substituted AlN (BAlN) is generally considered as an ultrawide bandgap semiconductor [111,112], and the measured optical bandgap for low B alloyed BAlN exhibiting ferroelectricity is larger than 5.2 eV, which could be beneficial for reducing the dielectric loss in nitride ferroelectrics [113,114]. Hexagonal BN (hBN) has long been used as dielectrics for 2D heterostructures and devices, and the optical properties and bandgap have been extensively studied [115][116][117].…”

Power Enhancement of 265 nm DUV-LED Flip-Chip by HVPE-AlN High-Temperature Annealing

“…Aluminum nitride (AlN) thin films have attracted a great amount of attention due to their large bandgap, high thermal conductivity, and high acoustic velocity at high temperatures [ 1 , 2 , 3 ]. AlN-based electronics hold great promise, particularly in the fields of deep ultraviolet light-emitting diodes (DUV-LEDs) and photodetectors for solar-blind technologies [ 4 , 5 , 6 ]. DUV-LEDs with high efficiency and reliability may be grown on bulk AlN single crystal substrates with a low dislocation density and sufficient size [ 7 , 8 ].…”