ABSTRACT
This paper reports on the influence of the passivation of pseudomorphic AlInAs/GalnAs HEMT by ECR-deposited Si3N4 on the electrical characteristics of the devices. It is pointed out that the passivation process leads to strong modifications of electrical parameters such as the transconductance gm, the threshold voltage Vth and the off-state breakdown voltage Vbd but that the magnitude of the effect is dependent on both the overall strain state of the HEMT structure and on the plasma conditions during the passivation process. Care has been taken to control the early stages of the passivation by a surface nitridation before the deposition of the Si3N4 encapsulating layer. The influence of the mechanical state of the epitaxial layers was investigated through a comparison between lattice matched (LM-HEMT), pseudomorphic (PM-HEMT) and strain compensated pseudomorphic HEMT (SCPM-HEMT).
