摘要(英) |
Despite years of research efforts, the external quantum efficiency of deep ultraviolet (DUV,
wavelength ≤ 290 nm) LEDs rarely exceed 20%, far below the level of visible LEDs. The main
reason is that the p-type contact layer of DUV LEDs must simultaneously fulfill the requirement of
high transparent and high conductive, which is extremely difficult to achieve with the commonly
used material, AlGaN. To address the issue, hexagonal boron nitride (hBN) is recently regarded as a
potential alternative to AlGaN. hBN has the characteristics of high energy band and low hole
activation energy, which can prevent light absorption and provide sufficient free hole concentration
in the p-type layer. Because of the two merits, hBN is an ideal p-type material for DUV LEDs. In
addition, the wide bandgap (6 eV) of hBN can form a large band offset with AlGaN, effectively
blocking the electron spill from quantum wells. The hole activation energy of boron nitride is
reported to be as low as 30 meV, which is much lower than the ~510 meV of AlN. With such small
activation energy, hBN can provide a large number of holes to enter the quantum well, enhancing
the quantum efficiency of DUV LEDs. The low hole activation energy can also lower the operating
voltage, reduce heat generation, and thus improve device lifetime. The above-mentioned advantages
make boron nitride a promising p-type material for DUV LEDs. |
參考文獻 |
[1] H. X. Jiang and J. Y. Lin, Hexagonal boron nitride for deep ultraviolet photonic devices. Semicond.
Sci. Technol. 29, 084003 (2014).
[2] X. H. Jiang et al. Reduction of the Mg Acceptor Activation Energy in GaN, AlN, Al0.83Ga0.17N
and MgGaδ-Doping (AlN)5/(GaN)1: The Strain Effect. J. Phys. D: Appl. Phys. 48, 475104 (2015).
[3] M. Soltani, R. Soref, T. Palacios, and D. Englund, AlGaN/AlN integrated photonics platform for
the ultraviolet and visible spectral range. Optics Express. 24, 25415-25423 (2016).
[4] R. A. Patil. et al. Size-controllable synthesis of Bi/Bi2O3 heterojunction nanoparticles using
pulsed Nd:YAG laser deposition and metal-semiconductor-heterojunction-assisted
photoluminescence. Nanoscale 8, 3565-3571 (2016).
[5] Seung Hee Lee. et al. Improvements in structural and optical properties of wafer-scale hexagonal
boron nitride flm by post-growth annealing. Scientific Reports. 9, 10590 (2019).
[6] Y. Zhang, et al. Direct observation of a widely tunable bandgap in bilayer graphene. Nature. 459,
820-823 (2009).
[7] Th. Böker, et al. “Band structure of MoS2, MoSe2, and a - MoTe2: Angle-resolved photoelectron
spectroscopy and ab initio calculations. Phys. Rev. B. 64, 235305 (2001).
[8] L. Wang, et al. Negligible Environmental Sensitivity of Graphene in a Hexagonal Boron
Nitride/Graphene/h-BN Sandwich Structure. ACS Nano. 6, 9314–9319 (2012).
[9] M. Bokdam, G. Brocks, M. I. Katsnelson, and P. J. Kelly. Schottky barriers at hexagonal boron
nitride/metal interfaces: A first-principles study. Phys. Rev. B. 90, 085415 (2014).
[10] Xu Yang, et al. Growth of hexagonal boron nitride on sapphire substrate by
pulsed-mode metalorganic vapor phase epitaxy, Journal of crystal Growth. 482, 1-8 (2018).
[11] Q. S. Paduano, M. Snure, and J. Shoaf. Effect of V/III ratio on the growth of hexagonal boron
nitride by MOCVD. Mater. Res. Soc. Symp. Proc. 1726, 1–6 (2015).
[12] Chuang-Yuan Chiu, Growth of High-Quality AlN Via Pulsed-Flow MOCVD. Master′s thesis.
35
National Central University. (2020).
[13] Chun-Pin Huang, High Quality AlN and BN Grown by MOCVD for Deep UV LEDs. Master
Thesis. National Central University. (2020).
[14] Chun-Pin Huang, et al. Crystal Transformation of Cubic BN Nanoislands to Rhombohedral
BN Sheets on AlN for Deep-UV Light-Emitting Diodes, ACS Appl. Nano Mater. 5285–5290 (2020).
[15] Y. Kobayashi, et al. Hexagonal Boron Nitride Grown by MOVPE, Journal of Crystal Growth.
310, 5048–5052 (2008).
[16] J. Iwański, et al. Delamination of Large Area Layers of Hexagonal Boron Nitride Grown
by MOVPE, Acta Physica Polonica A. 139, 457-461 (2021).
[17] Adama Mballo, et al. Towards P-Type Conduction in Hexagonal Boron Nitride: Doping Study
and Electrical Measurements Analysis of hBN/AlGaN Heterojunctions. Nanomaterials, 11, 211
(2021).
[18] Kenji Watanabe, et al. Far-ultraviolet plane-emission handheld device based on hexagonal boron
nitride. Nature Photonics. 3, 591–594 (2009).
[19] R. Dahal, et al. Epitaxially grown semiconducting hexagonal boron nitride as a deep ultraviolet
photonic material. Appl. Phys. Lett. 98, 211110 (2011)
[20] S. Majety, et al. Epitaxial growth and demonstration of hexagonal BN/AlGaN p-n junctions for
deep ultraviolet photonics. Appl. Phys. Lett. 100, 061121 (2012 |