氮化銦鎵藍光發光二極體效率衰退之抑制 Reduction of efficiency droop in Blue InGaN LEDs

氮化銦鎵藍光發光二極體效率衰退之抑制 Reduction of efficiency droop in Blue InGaN LEDs
2018/11/16 氮化銦鎵藍光發光二極體效率衰退之抑制 Reduction of efficiency droop in Blue InGaN LEDs 彰化師大物博二王尊信 Speaker: Tsun-Hsin Wang Advisor: Prof. Yen-Kuang Kuo Date: 2018/11/16

Tsun-Hsin Wang/BLL/NCUE
大綱研究動機 ~LED TV 研究結構 ~Epistar Inc. 研究工具 ~Crosslight APSYS 研究結果結論 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

LED TV時代來臨 2009年3月 Samsung以迅雷不及掩耳之勢，在Yahoo奇摩首頁刊登廣告，正式宣告LED TV時代的來臨 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

LED需求到2012年晶電 (2448)董事長李秉傑日前指出若依照目前全年月產能40億顆的產量計算，明年藍光就會出現供不應求的現象，如果產能無法在2012年前快速擴增，屆時加上照明的需求，產業鏈將嚴重失衡。 =>趕快買股票?! 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

晶元光電產學合作 p-GaN: 接觸層. p-AlGaN: 電子阻礙層(EBL). InGaN/GaN: 活性層triple quantum wells (well/barrier). n-GaN: 接觸層. u-GaN: 低溫成核層. p contact p-GaN p-AlGaN n contact InGaN/GaN n-GaN n-GaN u-GaN Sapphire Simplified Epistar LED structure. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

與實驗Curve fitting 光電元件相較於單一原子為複雜系統，因此精確與實務需要權衡然而，從LI與IV的curve fitting，我們可以相信所模擬的LED元件與實驗結構具有相同光性與電性以此為基礎，模擬後得到的優化結果可以當作實驗長晶的參考 =>R & D Division 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

高階模擬器工欲善其事，必先利其器超過NT$5,000,000. APSYS是一套通用的化合物半導體元件以及矽半導體元件模擬軟體，主要應用於半導體雷射以外的所有半導體元件對象: 有機發光二極體(OLED) 發光二極體(LED) 光偵測器(PD) 太陽能電池(SC) 電吸收調制器(EAM) 高電子移動率電晶體(HEMT) 異質接面雙極電晶體(HBT) 金氧半場效電晶體(MOSFET) 共振穿隧二極體(RTD) 行波半導體光學放大器(TWSOA) 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

理論模型泊松方程(Poisson equation):∇2V = −ρ /ε ，ρ 為自由電荷的體電荷密度，ε為介質的介電常數。連續方程(Continuity equation): ∇J + ∂ρ/ ∂ t = 0 ， J為電流密度， t為時間。光子複波動方程(Complex wave equation): ∇2W+k2(ε-β2)W=0 ，W 為光子的波函數。 k為波向量，ε為介電常數，β為實數本徵值。光子速率方程(Rate equation): ∂S/ ∂ t =c(g-α)/n ， n為材料的折射率，g為增益，α 為損失，S 為光子數。光子增益方程(Gain equation): g= α+[ln(1/R1R2)]2L，R為兩鏡的反射率，L為共振腔長。 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

參數表方程式 =>參數泊松方程 =>V, n, p 連續方程 => V, n, p, S, W, g 速率方程 => n, p, S, W, g 波動方程　　 => n, p, W, lambda, g 增益方程　　 => n, p, lambda, g V表電位、 n與p表電子與電洞濃度、 S表光子數目、W表光場強度、 lambda表波長、 g表增益 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

S-1. Higher p-doping of EBL
Structure A: Original structure, EBL p-doping= 1.2×1024 m-3. Structure B: Slight structure, EBL p-doping= 2×1024 m-3. Structure C: Heavy structure, EBL p-doping= 5×1024 m-3. p contact p-GaN p-AlGaN n contact InGaN/GaN n-GaN n-GaN u-GaN Sapphire 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Higher p-doping of EBL in InGaN LEDs
(Left figure) With more p-doping in EBL, the efficiency droop is suppressed markedly. (Right figure) The corresponding output power is enhanced at the same time. At high current injection, 140 mA for example, the output powers are about 2 and 4 times to original structure with optimized structure B and C respectively. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Simulation results (Middle figure) With slightly higher p-doping of EBL, the injections of both electron and hole are enhanced markedly. At the same time, the 2DEG is vanished. (Right figure) With heavily higher p-doping of EBL, even the uniformities of both electron and hole are enhanced. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Theory explanation 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

S-2. Lower aluminum-composition of EBL
Structure A: EBL: Al0.15Ga0.85N. Structure B: EBL: Al0.14Ga0.85In0.01N. Structure C: EBL: Al0.13Ga0.85In0.02N. Structure D: EBL: Al0.12Ga0.85In0.03N. Structure E: EBL: Al0.11Ga0.85In0.04N. p contact p-GaN p-AlGaN n contact InGaN/GaN n-GaN n-GaN u-GaN Sapphire 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Lower aluminum-composition of EBL in InGaN LEDs
(Left figure) With lower aluminum-composition of EBL, the efficiency droop is suppressed markedly. (Right figure) The corresponding output power is enhanced at the same time. At high current injection, 150 mA for example, the output powers of optimized structures are about 2 ~ 5 times to that of original structure. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Simulation results (Left figure) Electron concentration at 150 mA. (Right figure) Hole concentration at 150 mA. The origin of enhancement on IQE and output power is the increase of electron and hole concentration in all wells. What is more, they appears at the same time dramatically. (The same result is found by increasing p-doping concentration of EBL.) 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Theory explanation (Left figure) Conduction band diagram at 150 mA. The origin of enhancement on electron injection efficiency is the reduction of two dimension electron gas (2DEG) in conduction band. (Right figure) Valance band diagram at 150 mA. The origin of enhancement on hole injection efficiency is the reduction of effective potential height in valance band. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

S-3. Higher aluminum-composition of last barrier
Increase aluminum-composition of last barrier. Structure A: GaN. Structure B: Al0.01Ga0.99N. Structure C: Al0.02Ga0.98N. Structure D: Al0.03Ga0.97N. Structure E: Al0.04Ga0.96N. Structure F: Al0.05Ga0.95N. p contact p-GaN p-AlGaN n contact InGaN/GaN n-GaN n-GaN u-GaN Sapphire 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Higher aluminum-composition of last barrier in InGaN LEDs
(Left figure) With higher aluminum-composition of last barrier, the efficiency droop is suppressed. (Right figure) The corresponding output power is enhanced at the same time. At high current injection, 150 mA for example, the output powers of optimized structures are about 1~2 times to that of original structure. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Simulation results (Left figure) Electron injection is enhanced markedly. (Right figure) Hole injection is also enhanced markedly. The origin of enhancement on IQE and output power is the increase of electron and hole concentrations in, almost, all wells. What is more, they appears at the same time dramatically. The same results are found by increasing p-doping concentration and decreasing aluminum-composition of EBL. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Theory explanation 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

結論 In this study, three investigations of blue InGaN LEDs are proposed. Due to the dynamics of carrier transportation, the performance of InGaN LEDs is enhanced markedly. By reducing the effective potential height in valance band near EBL, the hole concentration in last well is increased. The origin of the optimization is increase of hole injection which makes the reduction of efficiency droop trustworthy. 2018/11/16 Tsun-Hsin Wang/BLL/NCUE

Thank you for your attention!
2018/11/16 Tsun-Hsin Wang/BLL/NCUE

氮化銦鎵藍光發光二極體效率衰退之抑制 Reduction of efficiency droop in Blue InGaN LEDs

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氮化銦鎵藍光發光二極體效率衰退之抑制 Reduction of efficiency droop in Blue InGaN LEDs

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