[1] [1] Shatalov M, Yang J W, Sun W H, et al. Efficiency of light emission in high aluminum content AlGaN quantum wells［J］. Journal of Applied Physics, 2009, 105(7): 073103.

[2] [2] Khan A, Balakrishnan K, Katona T. Ultraviolet lightemitting diodes based on group three nitrides［J］. Nature Photonics, 2008, 2(2): 7784.

[3] [3] Fischer A J, Allerman A A, Crawford M H, et al. Roomtemperature direct current operation of 290 nm lightemitting diodes with milliwatt power levels［J］. Applied Physics Letters, 2004, 84(17): 33943396.

[4] [4] Li D, Jiang K, Sun X, et al. AlGaN photonics: recent advances in materials and ultraviolet devices［J］. Advances in Optics & Photonics, 2018, 10(1): 43110.

[5] [5] Ellingson R J， Beard M C， Johnson J C, et al. Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots［J］. Nano Letters, 2005, 5(5): 865871.

[6] [6] Klimov V I， Mikhailovsky A A， Xu S, et al. Optical gain and stimulated emission in nanocrystal quantum dots［J］. Science, 2000, 290(5490): 314317.

[7] [7] Chuang L, Chang C S. A bandstructure model of strained quantumwell wurtzite semiconductors［J］. Semiconductor Science and Technology, 1999, 12(3): 252.

[8] [8] Stampfl C, Walle C G V D. Theoretical investigation of native defects, impurities, and complexes in aluminum nitride［J］. Physical Review B, 2002, 65: 155212.

[9] [9] Nam K B, Nakarmi M L, Li J, et al. Mg acceptor level in AlN probed by deep ultraviolet photoluminescence［J］. Applied Physics Letters, 2003, 83(5): 878880.

[10] [10] Wang S, Dai J N, Hu J H, et al. Ultrahigh degree of optical polarization above 80% in AlGaNbased deepultraviolet LED with motheye microstructure［J］. ACS Photonics, 2018, 5(9): 35343540.

[11] [11] Nam K B, Li J, Nakarmi M L, et al. Unique optical properties of AlGaN alloys and related ultraviolet emitters［J］. Applied Physics Letters, 2004, 84(25): 52645266.

[12] [12] Zhang J, Zhao H P, Tansu N. Effect of crystalfield splitoff hole and heavyhole bands crossover on gain characteristics of high Alcontent AlGaN quantum well lasers［J］. Applied Physics Letters, 2010, 97(11): 111105.

[13] [13] Lin W, Jiang W, Gao N, et al. Optical isotropization of anisotropic wurtzite Alrich AlGaN via asymmetric modulation with ultrathin (GaN)m/(AlN)n superlattices［J］. Laser & Photonics Reviews， 2013， 7(4)： 572579.

[14] [14] Han J, Crawford M H, Shul R J, et al. AlGaN/GaN quantum well ultraviolet light emitting diodes［J］. Applied Physics Letters, 1998, 73(12): 16881690.

[15] [15] Kawakami Y, Shen X Q, Piao G, et al. Improvements of surface morphology and sheet resistance of AlGaN/GaN HEMT structures using quasi AlGaN barrier layers［J］. Journal of Crystal Growth, 2007, 300(1): 168171.

[16] [16] Gorczyca I, Suski T, Christensen N E, et al. Theoretical study of nitride short period superlattices［J］. Journal of Physics. Condensed Matter, 2018， 30(6)： 063001.

[17] [17] Taniyasu Y, Kasu M. Polarization property of deepultraviolet light emission from Cplane AlN/GaN shortperiod superlattices［J］. Applied Physics Letters, 2011, 99(25): 251112.

[18] [18] Kuchuk A V, Kladko V P, Petrenko T L, et al. Mechanism of straininfluenced quantum well thickness reduction in GaN/AlN shortperiod superlattices［J］. Nanotechnology, 2014, 25(24): 245602.

[19] [19] Rong X, Wang X, Ivanov S V, et al. Highoutputpower ultraviolet light source from quasi2D GaN quantum structure［J］. Advanced Materials, 2016, 28(36): 79787983.

[20] [20] Islam S M, Lee K, Verma J, et al. MBEgrown 232270 nm deepUV LEDs using monolayer thin binary GaN/AlN quantum heterostructures［J］. Applied Physics Letters, 2017, 110(4): 041108.

[21] [21] Islam S M, Protasenko V, Lee K, et al. DeepUV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures［J］. Applied Physics Letters, 2017,111(9): 091104.

[22] [22] Shan M C, Zhang Y, Tran T B, et al. Deep UV laser at 249 nm based on GaN quantum wells［J］. ACS Photonics, 2019, 6(10): 23872391.

[23] [23] Toropov A A, Evropeitsev E A, Nestoklon M O, et al. Strongly confined excitons in GaN/AlN nanostructures with atomically thin GaN layers for efficient light emission in deepultraviolet［J］. Nano Letters, 2020, 20(1): 158165.

[24] [24] Ohba Y, Sato R. Growth of AlN on sapphire substrates by using a thin AlN buffer layer grown twodimensionally at a very low V/III ratio［J］. Journal of Crystal Growth, 2000, 221(1/2/3/4): 258261.

[25] [25] Zeimer U, Kueller V, Knauer A, et al. High quality AlGaN grown on ELO AlN/sapphire templates［J］. Journal of Crystal Growth, 2013, 377: 3236.

[26] [26] Hirayama H, Fujikawa S, Noguchi N, et al. 222282 nm AlGaN and InAlGaNbased deepUV LEDs fabricated on highquality AlN on sapphire［J］. Physica Status Solidi (a), 2009, 206(6): 11761182.

[27] [27] Sun W H, Zhang J P, Yang J W, et al. Fine structure of AlN/AlGaN superlattice grown by pulsed atomiclayer epitaxy for dislocation filtering［J］. Applied Physics Letters, 2005, 87(21): 211915.

[28] [28] Yoichi Kawakami，Mitsuru Funato，Ryan G. Initial nucleation of AlN grown directly on sapphire substrates by metalorganic vapor phase epitaxy［J］. Applied Physics Letters, 2008, 92(24): 241905.

[29] [29] Banal R G, Funato M, Kawakami Y. Characteristics of high Alcontent AlGaN/AlN quantum wells fabricated by modified migration enhanced epitaxy［J］. Physica Status Solidi C, 2010， 7(7/8): 21112114.

[30] [30] Wang H M, Zhang J P, Chen C Q, et al. AlN/AlGaN superlattices as dislocation filter for lowthreadingdislocation thick AlGaN layers on sapphire［J］. Applied Physics Letters, 2002, 81(4): 604606.

[31] [31] Zhuang Q Q, Lin W, Yang W H, et al. Defect suppression in AlN epilayer using hierarchical growth units［J］. The Journal of Physical Chemistry C, 2013, 117(27): 1415814164.

[32] [32] Gao N, Lin W, Chen X, et al. Quantum state engineering with ultrashortperiod (AlN)m/(GaN)n superlattices for narrowband deepultraviolet detection［J］. Nanoscale, 2014, 6(24): 1473314739.

[33] [33] Gao N, Feng X, Lu S, et al. Integral monolayerscale featured digitalalloyed AlN/GaN superlattices using hierarchical growth units［J］. Crystal Growth & Design, 2019, 19(3): 17201727.

[34] [34] Murotani H, Akase D, Anai K, et al. Dependence of internal quantum efficiency on doping region and Si concentration in Alrich AlGaN quantum wells［J］. Applied Physics Letters, 2012, 101(4): 042110.

[35] [35] Gupta H, Ahmad S, Kattayat S, et al. Improvement in efficiency and luminous power of AlGaNbased DUV LEDs by using partially graded quantum barriers［J］. Superlattices and Microstructures, 2020, 142: 106543.

[36] [36] Taniyasu Y, Kasu M, Makimoto T. Aluminum nitride deepultraviolet lightemitting diodes［J］. NTT Technical Review, 2006, 4(12): 5458.

[37] [37] Chen L, Zheng J J, Lin W, et al. Abnormal radiative interband transitions in highAlcontent AlGaN quantum wells induced by polarized orbitals［J］. ACS Photonics, 2017, 4(9): 21972202.

[38] [38] Chen L, Lin W, Wang H Q, et al. Reversing abnormal hole localization in highAlcontent AlGaN quantum well to enhance deep ultraviolet emission by regulating the orbital state coupling［J］. Light: Science & Applications, 2020, 9: 104.

[39] [39] Nakarmi M L, Kim K H, Li J, et al. Enhanced ptype conduction in GaN and AlGaN by Mgδdoping［J］. Applied Physics Letters, 2003, 82(18): 30413043.

[40] [40] Bayram C, Pau J L, Mcclintock R, et al. Deltadoping optimization for high quality ptype GaN［J］. Journal of Applied Physics, 2008, 104(8): 083512.

[41] [41] Kim K S, Han M S, Yang G M, et al. Codoping characteristics of Zn with Mg in GaN［J］. Applied Physics Letters, 2000, 77(8): 11231125.

[42] [42] Kipshidze G, Kuryatkov V, Borisov B, et al. Mg and O codoping in ptype GaN and AlxGa1-xN (0<x<0.08)［J］. Applied Physics Letters, 2002, 80(16): 29102912.

[43] [43] Aoyagi Y, Takeuchi M, Iwai S, et al. High hole carrier concentration realized by alternative codoping technique in metal organic chemical vapor deposition［J］. Applied Physics Letters, 2011, 99(11): 112110.

[44] [44] Simon J, Protasenko V, Lian C, et al. Polarizationinduced hole doping in widebandgap uniaxial semiconductor heterostructures［J］. Science, 2010, 327(5961): 6064.

[45] [45] Zhang L, Ding K, Yan J C, et al. Threedimensional hole gas induced by polarization in (0001)oriented metalface IIInitride structure［J］. Applied Physics Letters, 2010, 97(6): 062103.

[46] [46] Schubert E F, Grieshaber W, Goepfert I D. Enhancement of deep acceptor activation in semiconductors by superlattice doping［J］. Applied Physics Letters, 1996, 69(24): 37373739.

[47] [47] Kozodoy P, Hansen M, Denbaars S P, et al. Enhanced Mg doping efficiency in Al0.2Ga0.8N/GaN superlattices［J］. Applied Physics Letters, 1999, 74(24): 36813683.

[48] [48] Kozodoy P, Smorchkova Y P, Hansen M, et al. Polarizationenhanced Mg doping of AlGaN/GaN superlattices［J］.Applied Physics Letters, 1999, 75(16): 24442446.

[49] [49] Wang L, Li R, Li D, et al. Strain modulationenhanced Mg acceptor activation efficiency of Al0.14Ga0.86N/GaN superlattices with AlN interlayer［J］. Applied Physics Letters, 2010, 96(6): 061110.

[50] [50] Iwai S, Hirayama H, Aoyagi Y. High doped ptype GaN grown by alternative Codoping technique［J］. MRS Proceedings, 2002, 719： F1.1.

[51] [51] Li J C, Yang W H, Li S P, et al. Enhancement of ptype conductivity by modifying the internal electric field in Mgand Siδcodoped AlxGa1-xN/AlyGa1-yN superlattices［J］. Applied Physics Letters, 2009, 95(15): 151113.

[52] [52] Zhang Z Y, Kushimoto M, Sakai T, et al. A 271.8 nm deepultraviolet laser diode for room temperature operation［J］. Applied Physics Express, 2019, 12(12): 124003.

[53] [53] Goepfert I D, Schubert E F, Osinsky A, et al. Experimental and theoretical study of acceptor activation and transport properties in ptype AlxGa1xN/GaN superlattices［J］. Journal of Applied Physics, 2000, 88(4): 20302038.

[54] [54] Waldron E L, Graff J W, Schubert E F, et al. Improved mobilities and resistivities in modulationdoped ptype AlGaN/GaN superlattices［J］. Materials Research Society SymposiumProceedings， 2002， 693： 823828.

[55] [55] Zheng T C, Lin W, Liu R, et al. Improved ptype conductivity in Alrich AlGaN using multidimensional Mgdoped superlattices［J］. Scientific Reports, 2016, 6: 21897.

[56] [56] Park S H, Shim J I. Carrier density dependence of polarization switching characteristics of light emission in deepultraviolet AlGaN/AlN quantum well structures［J］. Applied Physics Letters, 2013, 102(22): 221109.

[57] [57] Northrup J E, Chua C L, Yang Z, et al. Effect of strain and barrier composition on the polarization of light emission from AlGaN/AlN quantum wells［J］. Applied Physics Letters, 2012, 100(2): 021101.

[58] [58] Wierer J J Jr， Montao I, Crawford M H, et al. Effect of thickness and carrier density on the optical polarization of Al0.44Ga0.56N/Al0.55Ga0.45N quantum well layers［J］. Journal of Applied Physics, 2014, 115(17): 174501.

[59] [59] Atsushi Yamaguchi A. Valence band engineering for remarkable enhancement of surface emission in AlGaN deepultraviolet light emitting diodes［J］.Physica Status Solidi C, 2008, 5(6): 23642366.

[60] [60] Jiang X H, Shi J J, Zhang M, et al. Enhancement of TE polarized light extraction efficiency in nanoscale (AlN)m/(GaN)n(m>n) superlattice substitution for Alrich AlGaN disorder alloy: ultrathin GaN layer modulation［J］. New Journal of Physics, 2014, 16: 113065.

[61] [61] Liu C, Ooi Y K, Islam S M, et al. Physics and polarization characteristics of 298 nm AlNdeltaGaN quantum well ultraviolet lightemitting diodes［J］. Applied Physics Letters, 2017, 110(7): 071103.

[62] [62] Liu C, Ooi Y K, Islam S M, et al. 234 nm and 246 nm AlNDeltaGaN quantum well deep ultraviolet lightemitting diodes［J］. Applied Physics Letters, 2018, 112(1): 011101.

[63] [63] Hou M J, Qin Z X, He C G, et al. Effect of injection current on the optical polarization of AlGaNbased ultraviolet lightemitting diodes［J］. Optics Express, 2014, 22(16): 1958919594.

[64] [64] Zheng J J, Li S Q, Chou C L, et al. Direct observation of the biaxial stress effect on efficiency droop in GaNbased lightemitting diode under electrical injection［J］. Scientific Reports, 2015, 5: 17227.

[65] [65] Zheng J J, Li J C, Zhong Z B, et al. Effect of electrical injectioninduced stress on interband transitions in high Al content AlGaN MQWs［J］. RSC Advances, 2017, 7(87): 5515755162.

[66] [66] Long H L, Wang S, Dai J N, et al. Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD［J］. Optics Express, 2018, 26(2): 680686.

[67] [67] Luo Z Y, Lu S Q, Li J C, et al. Modification of strain and optical polarization property in AlGaN multiple quantum wells by introducing ultrathin AlN layer［J］. AIP Advances, 2019, 9(5): 055004.