Ag–Pd–Cu alloy reflector to improve the opto-electrical performance and electromigration resistance of near ultraviolet GaN-based light-emitting diode

Han

et al. 2020

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We investigated the electrical property of reflective non-alloyed Rh contacts to p-Al0.45Ga0.55N contact layers and the performance of 278 nm flip-chip (FC) LEDs with the Rh and Ni/Au contacts as a function of Mg concentration. The three contact layers contained Mg concentration of 5.7 × 1019 cm−3 (sample A), 1.0 × 1020 cm−3 (sample B), and 1.4 × 1020 cm−3 (sample C). The Rh contacts to the sample A showed non-ohmic behaviour, while the samples B and C were ohmic with contact resistivity of 3.2 × 10−1 and 3.4 × 10−2 Ωcm2, respectively. The FC-LEDs with the sample A, B, and C with the Rh contacts yielded forward voltages of 7.26, 6.24, and 6.30 V, and output power of 10.46, 10.85, and 10.44 mW at 50 A cm−2, respectively, whereas that with the sample C (Ni/Au contact) gave 6.51 V and 6.26 mW. The FC-LEDs with p-Al0.55Ga0.45N (sample D) and p-Al0.61Ga0.39N (sample E) contact layers (with Mg dopant of 8.0 × 1019 cm−3) displayed forward voltage of 7.41 and 8.72 V at 50 A cm−2 and output power of 11.88 and 15.25 mW, respectively. The Wall-plug efficiency of the sample C, D, and E was estimated to be 3.31, 3.21, and 3.50%, respectively. These results show FC-LEDs fabricated with highly Mg-doped p-AlGaN and Rh contact demonstrate reliable performance upon operating at 100 A cm−2.

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confidence: 99%

Heavy Mg Doping to Form Reliable Rh Reflective Ohmic Contact for 278 nm Deep Ultraviolet AlGaN-Based Light-Emitting Diodes

Han

et al. 2020

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“…These shifts indicate that the surface Fermi levels move toward the valence band edge owing to the generation of acceptor-like Ga vacancies due to Ga out diffusion. 27,37,47 In other words, the Ag-Ga binary phase diagram indicates the high solubility of Ga atoms in Ag (18.7 at%) at approximately 600 °C. 48,49 Thus, Ga atoms are believed to outdiffuse into Ag to form an Ag-Ga solid solution upon annealing.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, many studies have been conducted to improve the thermal stability of Ag by employing, for example, capping layers, [21][22][23] interlayers, 24,25 and Ag alloys. [26][27][28] Kim et al 26 used an AgAl alloy p-type reflector in GaN-based flipchip (FC) LEDs. The AgAl reflector exhibited enhanced thermal stability and adhesion characteristics compared to the Ag-only scheme.…”

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confidence: 99%

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Electrical Characteristics of Thermally Stable Ag–Pd–Cu Alloy Schottky Contacts on n-Al_0.6Ga_0.4N

Sim

Kim

Seong

et al. 2022

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We report the fabrication of high-barrier-height and thermally reliable Schottky contacts to n-Al0.6Ga0.4N by using an Ag-Pd-Cu (APC) alloy. The Schottky barrier heights (SBHs) and ideality factors computed using the current-voltage (I-V) model ranged from 0.82 to 0.97 eV and from 3.15 to 3.44, respectively. The barrier inhomogeneity model and capacitance-voltage (C-V) method yielded higher SBHs (1.62–2.19 eV) than those obtained using the I-V model. The 300 ℃-annealed APC sample exhibited more uniform electrical characteristics than the 500 ℃-annealed Ni/Au Schottky samples (each with the best Schottky behavior). Furthermore, the scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) results indicated that the APC Schottky contacts were more thermally stable than the Ni/Au contacts. On the basis of the X-ray photoemission spectroscopy (XPS) results, the improved Schottky characteristics of the APC alloy contacts are described and discussed.

“…Because of a wide variety of applications, including solid-state lighting, resin curing, biological detection, molecular gas sensing, air cleaning, sterilization, and water purification, ultraviolet (UV) light emitters are of great technological importance. [1][2][3][4][5][6][7][8][9][10][11] Unlike mercurybased lamp, AlGaN UV emitters have smaller volume and can cover wide UV wavelength range of 210-400 nm by combining two binaries, e.g., AlN and GaN. 1 However, the external quantum efficiency (EQE) of deep UV light-emitting diodes (DUV LEDs) (wavelengths < 280 nm) was reported to be in the range of 1-7%.…”

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confidence: 99%

Improved Reliability of 278 nm Deep Ultraviolet AlGaN-Based Flip-Chip Light Emitting Diodes by Using ITO/Al Contact

Yum

Lim

et al. 2021

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We investigated the electrical and optical performance and reliability of 278 nm deep ultraviolet (DUV) AlGaN-based flip-chip light-emitting diodes (FCLEDs) fabricated with ITO/Al and reference Ni/Au contacts. The DUV FCLEDs with the Ni/Au and ITO/Al contacts yielded forward voltages of 6.52 and 6.65 V at 50 A cm−2 and light output of 6.36 and 10.06 mW at 50 A cm−2, respectively. The ITO/Al-based FCLEDs produced higher Wall plug efficiency (WPE) (3.04% at 50 A cm−2) than the Ni/Au-based samples (1.96%). The ITO/Al-based FCLEDs revealed 55% higher WPE at 50 A cm−2 than the Ni/Au-based sample. For both of the samples, the output power decreased with increasing operation time at 100 A cm−2. For example, after 2000 h, the Ni/Au and ITO/Al-based FCLEDs showed a reduction in the output power by 37% and 22%, respectively. Despite the good output characteristics, the ITO/Al contact-based FCLEDs exhibited higher forward bias voltages than the Ni/Au-based sample. Based on the energy dispersive X-ray spectroscopy (EDS) depth profiles, high-angle annular dark field (HAADF), and electron energy loss spectroscopy (EELS) results, reason for the increase in the forward voltage of ITO/Al-based FCLEDs is described and discussed.