載子遮蔽效應與壓電效應對氮化鎵發光二極體之光性影響研究;Carrier screening and piezoelectric effects on optical performance of GaN-based LED

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題名:	載子遮蔽效應與壓電效應對氮化鎵發光二極體之光性影響研究;Carrier screening and piezoelectric effects on optical performance of GaN-based LED
作者:	林宜瑾;Lin,Yi-chin
貢獻者:	化學工程與材料工程學系
關鍵詞:	發光二極體;氮化鎵;壓電場;載子遮蔽電場;熱膨脹係數;Light emitting diode;GaN;piezoelectric field;carrier screening field;CTE mismatch
日期:	2015-07-29
上傳時間:	2015-09-23 10:51:10 (UTC+8)
出版者:	國立中央大學
摘要:	發光二極體中的氮化鎵晶體具有壓電特性，產生之壓電場會使得主動層(多重量子井)之能階傾斜，此現象稱為量子侷限史塔克效應。能階傾斜造成載子侷限能力變差、載子在空間上分離(造成複合效率下降)。而載子空間分離會產生一載子遮蔽電場，其電場方向與壓電場相反，故可以減緩量子井之能階傾斜。本研究為探討壓電場與載子遮蔽電場之間的關係，及其對於發光二極體之光性的影響。藉由調變固晶製程之固晶溫度，我們發現高溫固晶可以釋放愈多氮化鎵磊晶薄膜中的壓應力，由這個發現，我們可以改變氮化鎵磊晶薄膜中的殘留壓應力，進而研究壓電場(由殘留應力造成)與載子遮蔽電場之間的關係。本論文首先提出:氮化鎵磊晶薄膜與藍寶石基板之間的熱膨脹係數不匹配造成之壓電場主導著氮化銦鎵多重量子井的能階傾斜。然而，減少熱膨脹係數造成之壓電場強度對發光二極體之光性並無太大的影響。這是因為載子遮蔽電場會抵消掉壓電場，而且我們認知到載子遮蔽電場的強度與壓電場造成之能階傾斜程度以及載子濃度有關。故進一步發展出載子遮蔽電場為熱膨脹係數造成之壓電場與外加電場的函數，之間的關係可表示為: 。本研究之兩個重大結論為:(1)熱膨脹係數造成之壓電場主導多重量子井的能階傾斜；(2)載子遮蔽電場是所有內部電場中影響發光二極體之發光特性最嚴重。;GaN crystal has the piezoelectric characteristic, the producing piezoelectric field would cause the energy level tilting in the InGaN MQWs, which is named as quantum-confinement Stark effect. Energy level tilting causes some disadvantages, i.e., the carrier confinement ability decay, the carrier spatial separation (reducing carrier recombination). The carrier spatial separation also causes a carrier screening effect with a direction opposite to the piezoelectric field, which could ease the quantum-confinement Stark effect. To explore the relationship between the piezoelectric field and the carrier screening effect, and their effects on the optical performance of the GaN-based LEDs. We adjust the process temperature of the die-attachment process, to vary the residual compressive stress in the GaN epilayer. We note that the higher temperature of the die-attachment process, the more compressive stress of the GaN LEDs can be released. By this concept, the residual compressive stress in the GaN epilayer could be controlled. In this Ph. D. study, we first propose that the CTE mismatch (between the GaN epilayer and the sapphire substrate) causes a CTE-induced piezoelectric field, which dominates the energy levels distortion in the InGaN MQWs of the GaN-based LEDs. However, the decreasing in the CTE-induced piezoelectric field does not have a significant effect on the optical performance of the GaN-based LEDs. One of the major reasons could be that the carrier screening effect could compensate the CTE-induced piezoelectric field. And, we realize that the magnitude of the carrier screening field depends on the piezoelectric field induced energy level tilting and the carrier concentration. Thus, the carrier screening field is a function of the CTE-induced piezoelectric field and applied electric field, which can be described as . Two major conclusions are: (1) the CTE-induced piezoelectric field dominates the initial energy level tilting in the InGaN MQWs; (2) the carrier screening effect is the major internal electric fields that influences the optical property of the GaN-based LEDs.
顯示於類別:	[化學工程與材料工程研究所] 博碩士論文

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