Abstract
Titanium/aluminum ohmic contacts to tapered n-type GaN nanowires with triangular cross-sections were studied. To extract the specific contact resistance, the commonly used transmission line model was adapted to the particular nanowire geometry. The most Al-rich composition of the contact provided a low specific contact resistance (mid10−8 Ωcm2) upon annealing at 600 °Cfor 15 s, but it exhibited poor thermal stability due to oxidation of excess elemental Al remaining after annealing, as revealed by transmission electron microscopy. On the other hand, less Al-rich contacts required higher annealing temperatures (850 or 900 °C) to reach a minimum specific contact resistance but exhibited better thermal stability. A spread in the specific contact resistance from contact to contact was tentatively attributed to the different facets that were contacted on the GaN nanowires with a triangular cross-section.
Highlights
The wide bandgap semiconductor GaN has attracted great attention for its use in electronic and optoelectronic devices, and its growth and properties have recently been explored in the form of a semiconductor nanowire (NW) because of its potential for transistors [1] and light emitting devices [2–4]
Ti, Cr, and Au have been used to form Schottky diodes [7, 12]. These reports demonstrate that the condition of the NW surface [5, 6] and the size of the GaN nanowire [10] can affect the characteristics of the contact
We examine Ti/Al contacts to n-type GaN nanowires by electrically probing the contacts and by examining them in cross-section using transmission electron microscopy (TEM)
Summary
The wide bandgap semiconductor GaN has attracted great attention for its use in electronic and optoelectronic devices, and its growth and properties have recently been explored in the form of a semiconductor nanowire (NW) because of its potential for transistors [1] and light emitting devices [2–4]. The metallizations Ti/Al/Pt/Au [6], Ti/Au [7, 8], Ni/Au [9], as well as Pt deposited by a focused ion beam [10, 11], have all been successfully used to form Ohmic type contacts to n-type GaN nanowires, sometimes with the assistance of annealing or premetallization ultraviolet (UV) ozone surface treatments. Ti, Cr, and Au have been used to form Schottky diodes [7, 12]. These reports demonstrate that the condition of the NW surface [5, 6] and the size of the GaN nanowire [10] can affect the characteristics of the contact. We examine Ti/Al contacts to n-type GaN nanowires by electrically probing the contacts and by examining them in cross-section using transmission electron microscopy (TEM). The effect of changing the ratio of Ti : Al on the specific contact resistance was studied as a function of annealing conditions, and differences in the thermal stability of the contacts were correlated to changes in the contact metallurgy
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