Aging and Stability of GaN High Electron Mobility Transistors and Light-Emitting Diodes With $\hbox{TiB}_{2}$- and Ir-Based Contacts

Abstract

There is interest in developing more stable contacts to a variety of GaN-based devices. In this paper, we give two examples of devices that show improved thermal stability when boride or Ir diffusion barriers are employed in ohmic-contact stacks. AlGaN/GaN high electron mobility transistors (HEMTs) were fabricated with Ti/Al/X/Ti/Au source-drain ohmic (where X is TiB 2 or Ir) contacts and were subjected to long-term annealing at 350 • C. By comparison with companion devices with conventional Ti/Al/Ni/Au ohmic contacts, the HEMTs with boride-based ohmic metal showed superior stability of both source-drain current and transconductance after 25 days of aging at 350 • C. The gate current for standard HEMTs increases during aging, and the standard ohmic contacts eventually fail by shorting to the gate contact. Similarly, InGaN/GaN multiple quantum well light-emitting diodes (MQW-LEDs) were fabricated with either Ni/Au/TiB 2 /Ti/Au or Ni/Au/Ir/Au p-ohmic contacts. Both of these contacts showed superior long-term thermal stability compared to LEDs with conventional Ni/Au contacts.

Reliability of GaN-Based HEMT devices

“…(4) Iridium and TiB 2 barrier layers on Ti/Al ohmics (RTA at 900°C) were recently shown to provide good stability up to 350°C over several days of stress [24].…”

Role of graphene interlayers in mitigating degradation of Ni/Au ohmic contact morphology on p-type GaN

“…The performance and reliability of GaN LEDs and laser diodes depends strongly on the quality of the p-Ohmic contact [1][2][3][4][5][6][7][8][9][10] . For low hole concentration materials like p-GaN, high work function metals such as Ni, Pd, Cr and Pt with an overlayer of Au are required for low resistivity contacts [4][5][6][7][11][12][13][14][15][16][17][18][19][20] . Ni-Au contacts are transparent on GaN, which is advantageous for optoelectronic applications [1][2][3][6][7][8] .…”