利用高反射性銀/鈀/銅合金之反射式電極應用於氮化鎵發光二極體之研究

Abstract

本篇論文主要是研究將鉻金屬附著層應用於反射式電極(銀合金/鉻/金以及銀/鉻/金)在氮化鎵發光二極體元件上之光電特性差異，期望以鉻/銀合金/鉻/金為條件的反射式電極其相較於鉻/銀/鉻/金為條件的反射式電極能具有高反射率值，使其應用在氮化鎵發光二極體元件上時能具有高的光輸出功率之外，更期望以鉻/銀合金/鉻/金為條件的反射式電極其分別在N-GaN上以及在ITO/P-GaN上時能具有較低的特徵接觸電阻值，使其應用在氮化鎵發光二極體元件之電極上時能夠更有效的降低元件整體之串聯電阻，進而使元件整體具有更低的導通電壓。 首先由量測反射率部份可得知，鉻/銀合金/鉻(10Å/600Å/500Å)、鉻/銀合金/鉻(20Å/600Å/500Å)、鉻/銀/鉻(10Å/600Å/500Å)與鉻/銀/鉻(20Å/600Å/500Å)在波段450nm的反射率值分別為89.9%、75.0%、92.2%與81.9%，相較於Cr/Au(500/800Å) 38.9%的反射率，皆具有高反射率值。 接著探討反射式電極(鉻/銀合金/鉻/金以及鉻/銀/鉻/金)分別在N-GaN上以及在ITO/P-GaN上之歐姆接觸特性研究。在反射式電極的條件為鉻/銀合金/鉻/金(10Å/600Å/500Å/800Å)、鉻/銀合金/鉻/金(20Å/600Å/500Å/800Å)、鉻/銀/鉻/金(10Å/600Å/500Å/800Å)與鉻/銀/鉻/金(20Å/600Å/500Å/800Å)時，分別於N-GaN以及ITO/P-GaN上其特徵接觸電阻值分別為5.49×10-4Ω-cm2、6.55×10-5Ω-cm2、9.61×10-4Ω-cm2、8.91×10-5Ω-cm2以及6.58×10-2Ω-cm2、5.96×10-2Ω-cm2、8.69×10-2Ω-cm2、7.82×10-2Ω-cm2，顯示出以鉻/銀合金/鉻/金為條件的反射式電極能夠有效地降低鉻/銀/鉻/金分別於N-GaN上以及ITO/P-GaN上較高的特徵接觸電阻值。 最後探討反射式電極(鉻/銀合金/鉻/金以及鉻/銀/鉻/金)在氮化鎵發光二極體元件上之光電特性研究。於操作電流為20mA時，在反射式電極的條件為鉻/銀合金/鉻/金(10Å/600Å/500Å/800Å)、鉻/銀合金/鉻/金(20Å/600Å/500Å/800Å)、鉻/銀/鉻/金(10Å/600Å/500Å/800Å)、鉻/銀/鉻/金(20Å/600Å/500Å/800Å)時，所對應的串聯電阻與導通電壓分別為23.2Ω、20.5Ω、33.6Ω、26.2Ω與3.25V、3.14V、3.58V、3.41V;以及所對應的光輸出功率與功率轉換效率分別為23.2mW、21.7mW、23.6mW、22.0mW以及42.3%、39.5%、43.1%、40.1%，其光輸出功率與功率轉換效率相較於傳統電極鉻/金(500Å/800Å)，分別提升了17.2%、9.6%、19.21%、11.0%以及11.6%、8.1%、3.1%、0.9%。 綜合以上光電特性分析可歸納出以鉻/銀合金/鉻/金為條件的反射式電極不僅能夠有效地降低鉻/銀/鉻/金在氮化鎵發光二極體元件上較高的串聯電阻與導通電壓之外，還能夠有效的增加鉻/銀/鉻/金在氮化鎵發光二極體元件上較低的功率轉換效率以及具有高光輸出功率輸出。

This paper mainly aims to study the differences in photoelectrical characteristics between reflective metal pads (APC/Cr/Au and Ag/Cr/Au) on a GaN-based light emitting diode device and the application of a chromium metal adhesion layer. Reflective metal pads with Cr/APC/Cr/Au are expected to have high reflectance than those with Cr/Ag/Cr/Au,these reflective metal pads with Cr/APC/Cr/Au also have high light output power when used on a GaN-based light emitting diode device. The reflective metal pads with Cr/APC/Cr/Au further have lower specific contact resistance when they are used on N-GaN and ITO/P-GaN, respectively. Therefore, their applications in a GaN-based light emitting diode device can more effectively reduce the series resistance of the entire device, thereby causing the overall device to have lower forward voltage. First, the measured reflectance reveals that the reflectance of Cr/APC/Cr(10Å/600Å/500Å), Cr/APC/Cr(20Å/600Å/500Å),Cr/Ag/Cr(10Å/600Å/500Å), and Cr/Ag/Cr(20Å/600Å/500Å) in the 450 nm wavelength are 89.9%, 75.0%, 92.2%, and 81.9%, respectively. They have higher reflectance by comparing with the reflectance of Cr/Au(500Å/800Å), i.e., 38.9%. Second, this paper studies the ohmic contact properties of reflective metal pads (Cr/APC/Cr/Au and Cr/Ag/Cr/Au) on N-GaN and ITO/P-GaN, respectively. Under the conditions of Cr/APC/Cr/Au(10Å/600Å/500Å/800Å), Cr/APC/Cr/Au (20Å/600Å/500Å/800Å),Cr/Ag/Cr/Au(10Å/600Å/500Å/800Å),and Cr/Ag/Cr/Au(20Å/600Å/500Å/800Å), their specific contact resistances on N-GaN and ITO/P-GaN are 5.49 × 10-4, 6.55 × 10-5, 9.61 × 10-4, 8.91 × 10-5 and 6.58 × 10-2, 5.96 × 10-2, 8.69 × 10-2, and 7.82 × 10-2 Ω-cm2, respectively. This finding shows that the reflective metal pads with Cr/APC/Cr/Au can more effectively reduce the higher specific contact resistances with Cr/Ag/Cr/Au on N-GaN and ITO/P-GaN. Third and last, this paper probes the photoelectric properties of reflective metal pads(Cr/APC/Cr/Au and Cr/Ag/Cr/Au) on a GaN-based light emitting diode device. Using a 20mA injection current, the corresponding series resistances are 23.2, 20.5, 33.6, and 26.2Ω, whereas the corresponding forward voltages are 3.25, 3.14, 3.58, and 3.41 V, respectively, under the conditions of Cr/APC/Cr/Au(10Å/600Å/500Å/800Å), Cr/APC/Cr/Au(20Å/600Å/500Å/800Å), Cr/Ag/Cr/Au(10Å/600Å/500Å/800Å), Cr/Ag/Cr/Au(20Å/600Å/500Å/800Å). Moreover, the corresponding light output powers are 23.2, 21.7, 23.6, and 22.0 mW, whereas the corresponding wall plug efficiencies are 42.3%, 39.5%, 43.1%, and 40.1%, respectively. Compared with conventional Cr/Au pad (500 Å/800 Å), their light output powers increase by 17.2%, 9.6%, 19.21%, and 11.0%, whereas their corresponding wall plug efficiencies increase by 11.6%, 8.1%, 3.1%, 0.9%, respectively. To sum up, reflective metal pads with Cr/APC/Cr/Au can more effectively reduce higher series resistances and forward voltages than those with Cr/Ag/Cr/Au on a GaN-based light emitting diode device. These reflective metal pads with Cr/APC/Cr/Au can also more effectively increase the low wall plug efficiency than those with Cr/Ag/Cr/Au on a GaN-based light emitting diode device and have high light output power.