Passivation of III-V-based compound semiconductor devices using high-density plasma deposited silicon nitride films

We report on the passivation of three kinds of III/V-based compound semiconductor devices using high-density plasma deposited silicon nitride (SiN) films. The devices are GaAs/AlGaAs quantum-well infrared photodetectors (QWIP), InGaAs/AlGaAs high-power lasers, and GaN-based high-electron mobility transistors (HEMT). It has been found that the deposition of SiN films has to be optimized for the specific application. For QWIP we have developed a room temperature SiN film exhibiting low mechanical stress (compressive 100 MPa), good adhesion to metal, and fairly high coefficient of thermal expansion. The film is highly conformal and has excellent step coverage. Using this film reliable QWIP-based IR (8-12 m) cameras in collaboration with AEG Infrarot-Module (AIM) GmbH, Heilbronn, Germany have been realized. The cameras are in operation ever since 5 years. For InGaAs/AlGaAs high-power lasers, we have developed a low-temperature (90°C) SiN film with low intrinsic stress (comp ressive 170 MPa) and a negligible hysteresis in stress upon thermal cycling. The reliability test of broad area laser diodes emitting at 880 run exhibited the lifetime of more than 10,000 h (based on a criterion of 20 % decrease in the initial output power of the laser) at 50°C after the emitting facet was coated with this SiN film. For GaN-based power devices low-temperature (240°C) different SiN films exhibiting high breakdown electric field strength (> 7.0 MV/cm) for metal-insulator-metal (MIM) capacitors on a Si substrate and a negligible hysteresis in stress upon thermal cycling have been developed. The DC-lifetime test of GaN/AlGaN HEMT device with gate length 0.3 m showed the lifetime of 450 h after passivation with a tensile SiN film. The cw output power density of 5.2 W/mm at 10 GHz and 35 V drain bias has been measured for a device periphery of 8×125 m.