Effect of Cl2 plasma treatment and annealing on vanadium based metal contacts to Si-doped Al0.75Ga0.25N

Abstract

In order to understand the electrical properties of V/Al/Ni/Au metal contacts to Si-doped Al0.75Ga0.25N layers, X-ray photoelectron spectroscopy analysis was performed on differently treated AlGaN:Si surfaces before metal deposition, and transmission electron microscopy was used to study the semiconductor-metal interface after contact annealing at 900 °C. Cl2 plasma etching of AlGaN increases the aluminum/nitrogen ratio at the surface, and Al oxide or oxynitride is always formed by any surface treatment applied after etching. After contact annealing, a complex interface structure including amorphous AlOx and different metal phases such as Al-Au-Ni, V-Al, and V2N were found. The electrical properties of the contacts were determined by thermionic emission and/or thermionic field emission in the low voltage regime. Nearly ohmic contacts on AlGaN surfaces exposed to a Cl2 plasma were only obtained by annealing the sample at a temperature of 815 °C under N2/NH3 prior to metallization. By this treatment, the oxygen contamination on the surface could be minimized, resulting in a larger semiconductor area to be in direct contact with metal phases such as Al-rich Al-Au-Ni or V-Al and leading to a contact resistivity of 2.5 × 10−2 Ω cm2. This treatment can be used to significantly reduce the operating voltage of current deep ultraviolet light emitting diodes which will increase their wall plug efficiency and lower the thermal stress during their operation.

Contact Engineering of III-Nitrides and Metal Schemes toward Efficient Deep-Ultraviolet Light-Emitting Diodes

“…After the annealing process, there exist several XRD peaks in electrode A, corresponding to the alloys including TiN, AlTi, and AlAu 2 . It is widely known that TiN facilitates the formation of ohmic contact on n-AlGaN. , For electrode B, additional XRD peaks appear and correlate with those of the Pt-related alloys containing Al 3 Pt 2 and TiPtAl. The surface roughness promotion can be attributed to these Pt-related alloys.…”

“…It is widely known that TiN facilitates the formation of ohmic contact on n-AlGaN. 48,53 For electrode B, additional XRD peaks appear and correlate with those of the Pt-related alloys containing Al 3 Pt 2 and TiPtAl. The surface roughness promotion can be attributed to these Pt-related alloys.…”

“…In the mesa definition process, etching damages, resulting from the plasma etching, generally act as deep-level compensation centers in Al-rich n-AlGaN. This increases the Schottky barrier height at the metal-AlGaN interface and raises the difficulty in forming ohmic contact. − To address such issue, various pretreatment approaches, including plasma treatment and/or additional annealing treatment under nitrogen ambient, have been proposed and conducted on etched n-AlGaN surface before metal schemes deposition. ,− Deep-level states or high-resistance oxidation layers could be effectively removed via these approaches, thus conducive to the formation of ohmic contact on Al-rich n-AlGaN. Based on the descriptions above, forming ohmic contact on Al-rich AlGaN is dominated by metal schemes, semiconductors, and their interaction, which calls for comprehensive investigation and advanced efforts toward engineering the properties of the electrical contact interface and understanding the basic mechanisms involved in DUV AlGaN-based LEDs.…”

Degradation analysis with characteristics and simulations of 265 nm UV-C LED

“…Since the physical mechanisms responsible for degradation of UV-LEDs have not been completely identi ed, numerous researches have been conducted on the reliability analysis of UV-LEDs in recent years [6][7][8]. It is known that the threading dislocations densities (TDD) and poor ohmic contacts with high Al-content AlGaN layers lead to a mass of Joule heating and non-radiative recombination heating in the device during operation which accelerates degradation [9,10].…”

Degradation analysis with characteristics and simulations of 265 nm UVC-LED

“…Since the physical mechanisms responsible for degradation of UV-LEDs have not been completely identi ed, numerous researches have been conducted on the reliability analysis of UV-LEDs in recent years [6][7][8]. It is known that the threading dislocations densities (TDD) and poor ohmic contacts with high Al-content AlGaN layers lead to a mass of Joule heating and non-radiative recombination heating in the device during operation which accelerates degradation [9,10].…”