Formation of thermally stable low-resistance Ti/W/Au ohmic contacts on n-type GaN

Abstract

A Ti(12 nm)/W(20 nm)/Au(50 nm) metallization scheme has been investigated for obtaining thermally stable low-resistance ohmic contacts to n-type GaN (4.0 × 10 18 cm −3 ). It is shown that the current-voltage (I-V) characteristics of the samples are abnormally dependent on the annealing temperature. For example, the samples that were annealed at temperatures below 750 • C for 1 min in a N 2 ambient show rectifying behavior. However, annealing the samples at temperatures in excess of 850 • C results in linear I-V characteristics. The contact produces a specific contact resistance as low as 8.4 × 10 −6 Ω cm 2 when annealed at 900 • C. It is further shown that the contacts are fairly thermally stable even after annealing at 900 • C; annealing the samples at 900 • C for 30 min causes insignificant degradation of the electrical and structural properties. Based on glancing angle X-ray diffraction and Auger electron microscopy results, the abnormal temperature dependence of the ohmic behavior is described and discussed.

Microanalysis of the Ti/Al and Ti/Al/Mo/Au ohmic contacts metallization to AlGaN/GaN heterostructures

“…In literature there are several works related to Ti/Al based ohmic contacts to AlGaN/GaN heterostructures where a different crystalline quality and various process parameters such as surface cleaning procedure, annealing conditions were investigated . There are attempts of fabrication of Al‐free ohmic contacts , but ohmic contacts based on Ti/Al bilayer annealed above 800 °C are still typically used to achieve low‐resistance ohmic contacts to AlGaN/GaN heterostructures.…”