AlN成核层对近紫外LED外延生长的影响
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摘要
在图形化蓝宝石衬底上制备了InGaN/AlGaN近紫外发光二极管(LED)。采用金属有机化学气相沉积(MOCVD)方法外延生长了不同厚度的AlN成核层,系统研究了AlN成核层厚度对外延层质量和InGaN/AlGaN近紫外LED(波长395 nm)光电性能的影响。使用透射电子显微镜对外延层的截面结构及位错进行表征。结果表明,随着AlN成核层厚度的增加,位错密度不断减小,且量子阱表面V形坑尺寸逐渐减小。LED器件的光学性能和电学性能随着V形坑尺寸的减小而提高,归一化外量子效率最大值由0.55增至1;在电流350 m A时,正向电压从3.54 V降至3.45 V,又升高至3.60 V。当AlN成核层厚度超过临界值后,位错密度不降反升,量子阱表面的V形坑密度增加,导致量子阱的有效发光面积减小,外延层质量下降。InGaN/AlGaN近紫外LED的光电性能与AlN成核层厚度密切相关,最佳AlN成核层厚度为50.22 nm。
InGaN/AlGaN near-ultraviolet( UV) light-emitting diodes( LEDs) were grown on patterned sapphire substrate. The AlN nucleation layers of different thicknesses were grown by the metal organic chemical vapor deposition( MOCVD) method. The effects of the thickness of AlN nucleation layer on the quality of the epitaxial layer and the photoelectric properties of InGaN/AlGaN near-UV LEDs( with a wavelength of 395 nm) were investigated systematically. The cross-section structure and dislocation of the epitaxial layer were characterized by the transmission electron microscope. The results show that the dislocation density and the size of the V-shaped pit on the quantum well surface decrease with the increase of AlN nucleation layer thickness. The optical and electrical properties of LED devices are improved with the decrease of the V-shaped pit size,and the maximum value of the normalized external quantum efficiency increases from 0. 55 to 1. The forward voltage at 350 m A drops from 3. 54 V to 3. 45 V initially,and then rises to 3. 60 V. When the thickness of the AlN nucleation layer exceeds the critical value,the dislocation density and the V-shaped pit density on the quantum well surface increase,whichleads to a decrease of the effective luminescence area and a decrease in the quality of the epitaxial layer.The photoelectric properties of InGaN/AlGaN near-UV LEDs are closely related to the AlN nucleation layer thickness,and the best AlN nucleation layer thickness is 50. 22 nm.
InGaN/AlGaN near-ultraviolet( UV) light-emitting diodes( LEDs) were grown on patterned sapphire substrate. The AlN nucleation layers of different thicknesses were grown by the metal organic chemical vapor deposition( MOCVD) method. The effects of the thickness of AlN nucleation layer on the quality of the epitaxial layer and the photoelectric properties of InGaN/AlGaN near-UV LEDs( with a wavelength of 395 nm) were investigated systematically. The cross-section structure and dislocation of the epitaxial layer were characterized by the transmission electron microscope. The results show that the dislocation density and the size of the V-shaped pit on the quantum well surface decrease with the increase of AlN nucleation layer thickness. The optical and electrical properties of LED devices are improved with the decrease of the V-shaped pit size,and the maximum value of the normalized external quantum efficiency increases from 0. 55 to 1. The forward voltage at 350 m A drops from 3. 54 V to 3. 45 V initially,and then rises to 3. 60 V. When the thickness of the AlN nucleation layer exceeds the critical value,the dislocation density and the V-shaped pit density on the quantum well surface increase,whichleads to a decrease of the effective luminescence area and a decrease in the quality of the epitaxial layer.The photoelectric properties of InGaN/AlGaN near-UV LEDs are closely related to the AlN nucleation layer thickness,and the best AlN nucleation layer thickness is 50. 22 nm.
引文
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[13]ZHANG B S,WU M,SHEN X M,et al.Influence of high-temperature AIN buffer thickness on the properties of Ga N grown on Si(111)[J].Journal of Crystal Growth,2003,258(1):34-40.
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[15]QUAN Z,WANG L,ZHENG C,et al.Roles of Vshaped pits on the improvement of quantum efficiency in In Ga N/Ga N multiple quantum well light-emitting diodes[J].Journal of Applied Physics,2014,116(18):779-789.
[16]LI H,LU T C.Study of efficiency droop in In Ga N/Ga N light emitting diodes with V-shape pits[J].Gallium Nitride Materials&Devices X,2015,9363:93631Q-1-93631Q-6.
[2]MATSUBARA T,DENPO Y,OKADA N,et al.Vshaped pits in HVPE-grown Ga N associated with columnar inversion domains originating from foreign particles ofα-Si3N4and graphitic carbon[J].Micron,2017,94:9-14.
[3]QUAN Z,LIU J,FANG F,et al.A new interpretation for performance improvement of high-efficiency vertical blue light-emitting diodes by In Ga N/Ga N superlattices[J].Journal of Applied Physics,2015,118(19):1606-1614.
[4]SHIN T,LI X S,KO D S,et al.Photocarrier dynamics near V-shaped pits in InxGa1-xN/Ga N multiple quantum wells[J].Chemical Physics,2014,436-437:51-54.
[5]孙晓园,张家骅,张霞,等.新一代白光LED照明用一种适于近紫外光激发的单一白光荧光粉[J].发光学报,2005,26(3):404-406.SUN X Y,ZHANG J H,ZHANG X,et al.A single white phosphor suitable for near ultraviolet excitation applied to new generation white LED lighting[J].Chinese Journal of Luminescence,2005,26(3):404-406(in Chinese).
[6]ZHANG M,CAI D M,ZHANG Y M,et al.Investigation of the properties and formation process of a peculiar V-pit in HVPE-grown Ga N film[J].Materials Letters,2017,198:12-15.
[7]KONG J,FENG M J,CAI J,et al.Ga N grown on nanopatterned sapphire substrates[J].Journal of Semiconductors,2015,36(4):26-29.
[8]CAO X A,TEETSOY J A,SHAHEDIPOUR S F,et al.Microstructural origin of leakage current in Ga N/In Ga N light-emitting diodes[J].Journal of Crystal Growth,2004,264(1/2/3):172-177.
[9]刘军林,熊传兵,程海英,等.Al N插入层对硅衬底Ga N薄膜生长的影响[J].光学学报,2014,34(2):311-316.LIU J L,XIONG C B,CHENG H Y,et al.Effects of Al N interlayer on growth of Ga N films on substrate[J].Acta Optica Sinica,2014,34(2):311-316(in Chinese).
[10]聂晓辉,王小兰,莫春兰,等.V形坑尺寸对硅衬底In Ga N/Al Ga N近紫外LED光电性能的影响[J].发光学报,2017,38(6):735-741.NIE X H,WANG X L,MO C L,et al.Effect of V-pit size on optical and electrical properties of In Ga N/Al Ga N near-ultraviolet light emitting diode[J].Chinese Journal of Luminescence,2017,38(6):735-741(in Chinese).
[11]邓旭光,韩军,邢艳辉,等.Al N成核层厚度对Si上外延Ga N的影响[J].光电子·激光,2013,2(7):1338-1343.DENG X G,HAN J,XING Y H,et al.Effect of Al N nucleation layer thickness on the quality of Ga N grown on Si(111)[J].Journal of Optoelectronics·Laser,2013,2(7):1338-1343(in Chinese).
[12]任凡.高质量Al N材料分子束外延生长机理及相关材料物理性研究[D].北京:清华大学,2010.
[13]ZHANG B S,WU M,SHEN X M,et al.Influence of high-temperature AIN buffer thickness on the properties of Ga N grown on Si(111)[J].Journal of Crystal Growth,2003,258(1):34-40.
[14]OKADA N,KASHIHARA H,SUGMOTO K,et al.Controlling potential barrier height by changing V-shaped pit size and the effect on optical and electrical properties for In Ga N/Ga N based light-emitting diodes[J].Journal of Applied Physics,2015,117(2):1274.
[15]QUAN Z,WANG L,ZHENG C,et al.Roles of Vshaped pits on the improvement of quantum efficiency in In Ga N/Ga N multiple quantum well light-emitting diodes[J].Journal of Applied Physics,2014,116(18):779-789.
[16]LI H,LU T C.Study of efficiency droop in In Ga N/Ga N light emitting diodes with V-shape pits[J].Gallium Nitride Materials&Devices X,2015,9363:93631Q-1-93631Q-6.