| Summary: | 碩士 === 國立交通大學 === 照明與能源光電研究所 === 102 === 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.
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