Future Works

7.2.1 Fabrication and characterization of ultra-low dislocation density LED with Two-step Maskless defects passivation layers

In our early reports, the low dislocation density LEDs with maskless defects passivation layer have been demonstrated. But, the high temperature molten KOH can only etch the screw type of dislocations, that’s why there still remain dislocations of other types. Based on the realization of high efficient light emitting devices, we will further fabricate ultra-low dislocation density LED by two-step maskeless defects passivation layers. The entire process flowchart and thin GaN structure are shown in Fig. 7.1. The epitaxial layers of two-step LED

structure were grown by metal-organic chemical vapor deposition (MOCVD). First, we grew 2 µm GaN on sapphire as a template, and the GaN epilayer was etched in molten KOH for 10 min at high temperature (approximate 250 ~ 300 degree).After several minutes of etching by KOH, defects on the surface of GaN epilayer were etched into pits, and the etching depth was approximately 1µm. Afterward the 1µm SiO2 film was deposited on the etched surface by plasma enhanced chemical vapor deposition (PECVD). The SiO2 film was used as defects-passivation layer.

And then we remove the sacrificial SiO2 film on top of the GaN by chemical mechanical polishing (CMP) to expose the GaN top layer which acts as the regrowth seed layer for next step crystal overgrowth. In order to further investigate the dislocation type etched by various solutions, we repeat above process using H3PO4 to etch the difference type dislocation.

Finally, LED structures were grown on two-step DP layer.

Fig. 7.1 The process flowchart for fabrication of two-step DP-LED

KOH Etching Deposit SiO₂ DP layer After CMP process Sapphire

Publication lists

Journal paper

[1] Ming-Hua Lo, Po-Min Tu, Chao-Hsun Wang, Cheng-Wei Hung, Shih-Chieh Hsu, Yuh-Jen Cheng, Hao-Chung Kuo, Hsiao-Wen Zan, Shing-Chung Wang, Chun-Yen Chang, and Shih-Cheng Huang―Defect selective passivation in GaN epitaxial growth and its application to light emitting diodes‖ Appl. Phys. Lett., 95, 211103, (2009) [2] Ming-Hua Lo, Chao-Hsun Wang, Po-Min Tu, Cheng-Wei Hung, Shih-Chieh Hsu, Yuh-Jen Cheng, Hao-Chung Kuo¹, Hsiao-Wen Zan , Shing-Chung Wang , Chun-Yen Chang and Che-Ming Liu ―High efficiency light emitting diode with anisotropically etched GaN-sapphire interface‖ Appl. Phys. Lett., 95, 041109, (2009)

[3] S. W. Chen, M. H. Lo, T. T. Kao, C. C. Kao, J. T. Chu, L. F. Lin, H. W. Huang, T. C.

Lu, H. C. Kuo, S. C. Wang, C. C. Kuo, and C. C. Lee, ―Effects of Inhomogeneous Gain and Loss on Nitride-based Vertical-Cavity Surface Emitting Lasers‖ Jpn. J. Appl. Phys., 48, 04C127 (2009)

[4] C.H. Chiu, S. Y. Kuo, M. H. Lo, T.C. Wang, Y. T. Lee, H. C. Kuo, T. C. Lu, and S. C.

Wang, ―Optical Properties of a-plane InGaN/GaN Multiple Quantum Wells on r-plane Sapphire Substrates with Different Indium Compositions,‖ J. Appl. Phys., 105, N6, 063105 (2009)

[4] Zhen-Yu Li, Wu-Yih Uen, Ming-Hua Lo, Ching-Hua Chiu, Po-Chun Lin, Chih-Tsang Hung, Tien-Chang Lu, Hao-Chung Kuo, Shing-Chung Wang, and Yen-Chin Huang ―Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates ‖ J. Electrochem.

Soc. 156, H129 (2009)

[5] Z. Y. Li, T. C. Lu*, H. C. Kuo, S. C. Wang M. H. Lo, and K. M. Lau ―HRTEM investigation of high reflectance AlN/GaN Distributed Bragg Reflectors by inserting AlN/GaN supperlattice,‖ J. Crystal Growth, 311, 3089 (2009)

[6] Z. Y. Li, M. H. Lo, C. H. Chiu, P. C. Lin, T. C. Lu, H. C. Kuo, S. C. Wang,

―Carrier localization degree of InGaN/GaN multiple quantum wells grown on vicinal sapphire substrates,‖ J. Appl. Phys., 105, 013103 ( 2009)

[7] C. H. Chiu, Zhen-yu Li, C. L. Chao, M. H. Lo, H. C. Kuo, P. C. Yu, T. C. Lu, and S. C. Wang, K. M. Lau, S. J. Cheng, ―Efficiency Enhancement of UV/Blue Light Emitting Diodes via Nanoscaled Epitaxial Lateral Overgrowth of GaN on a SiO₂ Nanorod-Array Patterned Sapphire Substrate,‖ J. Crystal Growth, 310,5150 (2008) [8] T. S. Ko, T. C. Lu, T. C. Wang, J. R. Chen, M. H. Lo, R. C. Gao, H. C. Kuo, and S.

C. Wang, J. L. Shen ―Optical characteristics of a-plane InGaN/GaN multiple quantum wells with different well width grown by metal-organic chemical vapor deposition‖, J.

Appl. Phys., 104, 093106 (2008)

[9] Z.Y. Li, M. H. Lo, C.T. Hung, S.W. Chen, T. C. Lu, H. C. Kuo and S. C. Wang

―High quality ultraviolet AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique‖, Appl. Phys. Lett., 93, 131116, (2008)

[10] C.H. Chiu, M. H. Lo, T. C. Lu, P. Yu, H.C. Kuo, H. W. Huang, and S.C. Wang,

―Nano-processing Techniques Applied in GaN-based Light Emitting Devices with Self-assembly Ni Nano-masks‖, IEEE J. Lightwave Tech.,26,1445 (2008)

[11] Ching-Hua Chiu, Chia-En Lee, Ming-Hua Lo, Hung-Wen Huang, Tien-Chang Lu, Hao-Chung Kuo and Shing Chung Wang ―Metal organic chemical vapor deposition growth of GaN-based light emitting diodes with naturally formed nano pyramids‖, Jpn. J. Appl. Phys., 47, 2954 (2008)

[12] Zhen-Yu Li, Wu-Yih Uen, Ming-Hua Lo, Ching-Hua Chiu, Po-Chun Lin, Chih-Tsang Hung, Tien-Chang Lu, Hao-Chung Kuo, Shing-Chung Wang, Yen-Chin Huang, ―Enhancing the emission efficiency of In_0.2Ga_0.8N/GaN MQW blue LED by using appropriately misoriented sapphire substrates,‖ J. Electrochem. Soc., 156, H129 (2008)

―Improvement of efficiency and ESD characteristics of ultraviolet light emitting diodes by inserting AlGaN and SiN buffer layers‖, J. Crystal Growth, 305,55 (2007) [15] T. S. Ko, T. C. Lu, T. C. Wang, M. H. Lo, J. R. Chen, R. C. Gao, H. C. Kuo, S. C.

Wang ―Optical characteristics of a-plane InGaN multiple quantum wells with different well width‖, Appl. Phys. Lett., 90, 181122, (2007), also selected for the June 2007

issue of Virtual Journal of Ultrafast Science

Conference paper

[1] Ming-Hua Lo et al. ―Output power enhancement of light-emitting diodes with defect passivation layer‖ Proc. SPIE 7602, 76021X (2010)

[2] Ming-Hua Lo, Po-Min Tu, Chao-HsunWang, Hao-Chung Kuo, Shing-Chung Wang, Hsiao-Wen Zan, Chun-Yen Chang, Shih-Chieh Hsu, Yuh-Jen Cheng and

Shih-Cheng Huang ―Multilayer Epitaxial Lateral Overgrowth of Light Emitting Diode with Anisotropically Etched GaN/Sapphire Interface‖ Late News, SSDM (2009)

[3] M. H. Lo, S.W. Chen Z.Y. Li. T. C. Lu, H. C. Kuo and S. C. Wang ―AlGaN/GaN multiple quantum wells grown by atomic layer deposition Lasers‖ 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS (2008).

[4] M. H. Lo, Z. Y. Li, J. R. Chen, T. S. Ko, T. C. Lu, H. C. Kuo, and S. C. Wang

―AlGaN/GaN multiple quantum wells grown by atomic-layer deposition‖

Proc. SPIE 6894, 68941V (2008)

[5] Ming-Hua Lo, Zhen-Yu Li, Shih-Wei Chen, Jhih-Cang Hong, Ting-Chang Lu, Hao-Chung Kuo, Shing-Chung Wang ―AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique‖ 1068-C05-07 MRS (2008)

[6] C. H. Chiu, C. L. Chao, M. H. Lo, Y. J. Cheng, H. C. Kuo, P. C. Yu, T. C. Lu, S. C.

Wang, and K. M. Lau ―Epitaxial Lateral Overgrowth of GaN-based Light Emitting Diodes on SiO2‖ Nanorod-Array Patterned Sapphire Substrates by MOCVD Proc.

SPIE 7135, 71351Z (2008)

Patent

[1] Ming-Hua Lo, Yuh-Jen Cheng, and Hao-Chung Kuo ―Method for fabricating GaN substrates and devices’’ 製作氮化鎵基板及元件之方法 (美國，台灣申請中) [2] Ming-Hua Lo, Yuh-Jen Cheng, and Hao-Chung Kuo ―Fabrication of GaN

substrate by defect selective passivation’’ 以缺陷防護層製作氮化鎵基板半導体元 件之方法 (美國，台灣申請中)

[3] Ming-Hua Lo, Yuh-Jen Cheng, and Hao-Chung Kuo’’Method for fabricating semiconductor substrates and smiconductor devices‖ 製作氮化鎵基板之方法 (美國，台灣申請中)