Evidence of deep-level defects in an MQW electroabsorption modulator through current-voltage and electrical noise characterization

This paper presents experimental and theoretical results concerning the cur rent-voltage and electrical noise characteristics of an integrated electroa bsorption modulator without illumination. Two components were studied: a de vice whose current-voltage and electrical noise characteristics were repres entative of the expected behavior and one exhibiting much higher leakage cu rrents and different noise spectra. The first part of the paper contains a detailed description of the structure of the studied components. In the sec ond part, the dark current of modulators is modeled using a thermal or phon on-assisted tunneling current process via electron traps thought to be loca lized at the multiquantum-well interfaces of the modulator's active layer. This model allows us to deduce the energy levels of the traps involved and demonstrates that the concentrations of the electron traps can vary by seve ral orders of magnitude between the components. In the third part, measurem ents of electrical noise and the modeling of these measurements allow us to show that the current generation mechanisms involve deep levels of carrier s with a continuous energy distribution which is of different width in the two components. In the fourth part, the dynamic chirp of the modulator is a nalyzed. The characteristic of the Henry modulator parameter (alpha(H)) as a function of the applied voltage is given for each of these two components . The difference between the two curves can be attributed to deep levels of carriers.