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 current-voltage and electrical noise characteristics of an integrated electroabsorption modulator without illumination. Two components were studied: a device whose current-voltage and electrical noise characteristics were representative of the expected behavior and one exhibiting much higher leakage currents and different noise spectra. The first part of the paper contains a detailed description of the structure of the studied components. In the second part, the dark current of modulators is modeled using a thermal or phonon-assisted tunneling current process via electron traps thought to be localized 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 several orders of magnitude between the components. In the third part, measurements of electrical noise and the modeling of these measurements allow us to show that the current generation mechanisms involve deep levels of carriers 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 analyzed. 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.