垂直結構之高功率氮化鎵發光二極體，可以減少元件內部電流擁擠效應及降低串聯電阻的作用，而在後續的封裝過程中，目前業界多採用錫-基金屬焊材，然而在其製程所涉及高溫製程與溫度變化，極易因金屬基板與epi-GaN間熱膨脹係數的差異造成元件發生形變，影響發光復合效率以及光輸出特性。本論文透過採用鋁摻雜之氧化鋅薄膜與區塊化的氧化鎳金歐姆接觸，分別做為減緩熱膨脹差異之緩充層與蕭特基阻障為電流擴散結構，與習之標準垂直結構元件相較，光輸出提升25%，光電轉換效率改善21%。在經過280℃、40s熱處理，仍保有穩定光析出特性。
基於 n-GaN(n=2.5) 與空氣(n=1) 折射率差距較大，光在行徑兩介質層之間，易產生Fresnel Loss與臨界角全反射損失。因此本研究另採用氧化鋅鋁(n=1.8~2.1) 於n-GaN 表面做為抗反射層期以減緩Fresnel 與 Snell 耗損 。實驗結果顯示，於350 mA電流輸入時，光輸出與標準垂直結構元件相較之下，可獲得 4.86%之提升。本研究所提元件之結構因抗反射膜所提升之光析出與KOH所致之表面粗化以提高光析出之效果兩者之間存在一互補且競合之機制。

Vertical structure metal substrate GaN-based light-emitting diodes (VM-LEDs) have continuously attracted great attentions for its superior electrical and optical performance. Use of metallic substrates, in particular, significantly improved the thermal management of VM-LEDs and made VM-LEDs better candidates to boost GaN-based LEDs in high power applications.
To package these vertical high power LED chips, tin-based solder material is preferable for die-bonding processes due to its better thermal conductivity. However, the temperature variation during die-bonding would be generally over 200oC depending on the alloy composition. This gives rise to additional stresses/strains from essentially large mismatches of coefficient of thermal expansion (CTE) between the epi-GaN and underlying metal layers. Thus the intrinsic polarization states are altered, and in turn electroluminescence (EL) characteristics, and irradiative recombination efficiency are affected.
In this work, we managed to alleviate this situation by inserting a sputter-deposited aluminum-doped zinc-oxide (AZO) layer between p-side ohmic contacts (oxidized Ni/Au) and the underlying metal layers for its less mismatching CTE and good as-deposited optical properties. In addition, the oxidized Ni/Au was patterned to expose p-GaN to form a Schottky blocking region with the AZO layer under the n-electrode area. This will force the current spread outward and enhance current spreading in the periphery area of the proposed device (namely SR-LEDs). Based on the experimental results, the light output power was 25% improved and this contributed to the enhancement of power conversion efficiency of 21%. In addition, SR-LEDs exhibited highly stable EL characteristics through out the thermal process up to 280oC for 40s as an emulation of die-bonding. On the other hand, a 12% drop in EL intensity of VM-LEDs was found.
To alleviate Fersnel and Snell loss, AZO film was sputter-deposited atop n-GaN as an anti-reflection layer for light extraction enhancement. Based on our experimental results, the light output intensity was improved by 4.86% improved. According to the surface morphology characterized by SEM, this relatively less improvements was mainly because the deposited AZO smoothed the roughened n-GaN and deducted part of the improvement from surface treatment with KOH. The light output intensity improvement could be further boosted through tailoring the thickness of AZO anti-reflection layer and the degree of n-GaN roughness.

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