The feasibility of using novel Cu/Mo/Ge/Pd ohmic contacts on n +-GaAs for heterojunction bipolar transistors (HBTs) is investigated. The electrical and material characteristics of the Cu/Mo/Ge/Pd/n +-GaAs structure were studied. After thermal annealing at 350°C, the specific contact resistances of the copper ohmic contacts Cu/Mo/Ge/Pd were measured to be 2.8 × 10-7 Ω cm2. Judging from the data of sheet resistance, X-ray diffraction analysis, Auger electron spectroscopy, and transmission electron microscopy, the Cu/Mo/Ge/Pd contact structure was very stable after annealing at 350°C. However, after 400°C annealing, the reaction of copper with the underneath layers started to occur and formed MoGe2, Cu3Ga and Ge3Cu phases. An InGaP/GaAs HBT with Cu/Mo/Ge/Pd contact metals was fabricated and compared with an HBT fabricated with traditional Au/Ni/Ge/Au contact metals. These two kinds of HBTs showed similar device characteristics. After reaching thermal stability and performing a high current-accelerated stress test at a current density of 120 kA/cm2 for 24h, the device with the Cu/Mo/Ge/Pd ohmic contacts still exhibits excellent electrical characteristics.
|Number of pages||4|
|Journal||Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers|
|State||Published - 15 Dec 2006|
- Copper metallization
- Heterojunction bipolar transistor
- Ohmic contact