Electrical and structural properties of low-resistance Ti/Al/Re/Au ohmic contacts to n-type GaN

Abstract

Titanium (15 nm)/aluminum (60 nm)/rhenium (20 nm)/gold (50 nm) ohmic contacts to moderately doped n-type GaN (4.07 ϫ 10 18 cm Ϫ3 ) have been investigated as a function of annealing temperature. It is shown that the currentvoltage (I-V) characteristics of the contacts are improved upon annealing at temperatures in the range of 550-750°C. Specific contact resistance as low as 1.3 ϫ 10 Ϫ6 Ωcm 2 is obtained after annealing at 750°C for 1 min in a nitrogen ambient. X-ray photoemission spectroscopy (XPS) results show that the Ga 2p core level for the sample annealed at 750°C shifts toward the high binding side by 0.71 eV compared with that of the as-deposited one. It is also shown that the contact does not seriously suffer from thermal degradation even when annealed at 750°C for 30 min. Based on Auger electron spectroscopy (AES), glancing angle x-ray diffraction (GXRD), and XPS results, possible explanations for the annealing-induced improvement of the ohmic behavior are described and discussed.

Thermally stable Ge/Cu/Ti ohmic contacts to n-type GaN

“…annealing time at 690°C. Comparison of our results with recently reported 34,35 values indicates that the surface roughness of the metal contact from this study is superior to those reported in the literature. This is believed to be due to the lower annealing temperature required to realize the ohmic behavior for the metallization used in this study and good thermal stability of the e 1 -Cu 3 Ge phase.…”

Recent Progresses in GaN Power Rectifier

“…In the literature, sophisticated metal layer stacks are currently under study, such as Ti/Al/Ni/Au, Ti/Al/Mo/Au and many others. 15,16,30) The specific contact resistance (SCR) values, image of the contact quality, are generally found from 10 À4 to few 10 À6 Ácm 2 , depending on metal stack, GaN doping level or annealing conditions. These contacts derive from the ones primarily used on the AlGaN top layer of HEMT structures [43][44][45][46] since they provide also good ohmic contacts.…”

“…[7][8][9] Extensive efforts have been made to achieve high-quality GaN layer grown by heteroepitaxy on sapphire and silicon wafers, [10][11][12][13][14] leading to structures now compatible with rectifying devices at more reasonable cost. If an abundant literature can be found on both ohmic and rectifying contacts, [15][16][17][18][19][20][21][22][23][24][25] central parts of the Schottky devices, few papers present complete structures and their performances. [26][27][28] As presented in Fig.…”

Micro- and nano-structural characterization of silicon carbide and related materials, for power devices, using TEM

“…Recent studies focused also on the various combinations of multilayer ohmic contacts like Ti/Al/barrier layer/Au. The barrier layer is often one of the metals such as Pt, Ti [137], Mo [138,139], Pd [140]or Ni [141], Re [142], and Ir [143] . The barrier layer was meant to keep in-diffusion of Au and outdiffusion of Al and Ti as low as possible.…”

“…In general, Ti was widely used as barrier layer and achieved low-specific contact resistivity at various thickness multilayer combinations. In addition, recent studies Mo was considered Mo as an alternative to the Ti barrier because of its low Au solubility (less than 1%) at elevated temperatures of 800 -900 °C [139,142].…”