Electrical and microstructural properties of thermally annealed Ni/Au and Ni/Pt/Au Schottky contacts on AlGaN/GaN heterostructures

Abstract

High work-function metals such as Ni, Pt, and Au in the form of multilayer structures, Ni/Au and Ni/Pt/Au, have been investigated as Schottky metallizations on AlGaN/GaN heterostructures under thermal annealing. As-deposited Ni/Pt/Au had slightly higher Schottky barrier height than its Ni/Au counterpart. Schottky barrier heights for Ni/Au diodes on AlGaN/GaN increased by about 20% from 1.02 eV for as-deposited to 1.21 eV after annealing at 500 °C for 2 min. Similar trends were observed for Ni/Pt/Au Schottky diodes. Thermal stability study for these devices showed that the interposition of Pt in Ni/Au systems improved the characteristics of the Schottky diodes after short-term anneal but cause significant degradation after long-term anneal at 500 °C. Ni/Au Schottky contacts exhibited excellent leakage response under thermal annealing for long periods. Microstructural studies were carried out on Ni/Pt/Au and Ni/Au Schottky contacts to elucidate the role of the Pt interlayer in the degradation of the Ni/Pt/Au metallization under longterm thermal anneal.

Effect of rapid thermal annealing on barrier height and 1/f noise of Ni/GaN Schottky barrier diodes

“…18 GaN based SBDs with barrier heights around 1.0 eV using different metals, like Pt, Pd, Ni, etc., have been already demonstrated. [23][24][25][26][27] As thermal stability of metal contacts is important for device operations at high temperatures and in harsh environments, several authors studied the effect of high temperature furnace annealing on Schottky barrier parameters in GaN based devices. [28][29][30][31] In most of these reports, furnace annealing is done for a relatively longer period (5-60 min) where Schottky barriers are found to degrade with increase in annealing temperature.…”

Electrical and Thermal Stability of ALD-Deposited TiN Transition Metal Nitride Schottky Gates for AlGaN/GaN HEMTs

“…The increased reverse leakage may be due to the lower TiN barrier height with the AlGaN (0.5 eV for TiN versus 0.7 eV for Ni, as calculated from temperaturedependent gate I-V measurements), or to the formation of a leaky interfacial layer in the initial stages of TiN deposition. 6,7,[17][18][19] The 2DEG density (n s ) and carrier mobility (μ 2DEG ) were found to be degraded more (relative to the as-grown structure) in the reference sample than in the sample subjected to the TiN ALD growth process. The degradation was largely attributed to fluorination of the AlGaN barrier under the gate during the SiN x recess etch process.…”

New approach for an accurate Schottky Barrier Height's extraction by I-V-T measurements

“…Some devices (virgin transistors) also reveal a lower SBH at lower temperatures, as a consequence of the lower leakage current, where at least two Schottky diodes seem to contribute. Furthermore, these lower values of the SBH can be correlated with an imperfection of the Schottky contact (pits, cracks with activation energies ranging from 1.05eV to over 2.2eV [6]), as the gate stack is composed by 3 metals (Ni/Pt/Au) which can mix and form intermediate mixtures [4], [5]. On the other hand, unrealistic low values are also obtained from the analysis (~ 0.1eV) which cannot be associated to a SBH.…”

“…2 discriminates f these diodes: φ B increases 000/T) for the lower 0.5eVemperature (thus, increases . Consequently, the lower e the one which dominates, e (main diode at high at low temperature, ue of 0.5eV for the SBH the virgin device can be ed metals [4], [5]. 2 that the sign of the slopes virgin devices at high temperature.…”