Influence of surface nitridation and of strain effect on the electrical characteristics of pseudomorphic AlInAs/GaInAs HEMT passivated with ECR-deposited Si_3N_4

摘要

This paper reports on the influence of the passivation of pseudomorphic AlInAs/GaInAs HEMT by ECR-deposited si_3N_4 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 g_m, the threshold voltage V_(th) and the off-state breakdown voltage V_(bd) 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 berfore the deposition of the Si_3N_4 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).