InGaAs self-assembly quantum dot for high-speed 1300 nm electroabsorption modulator

Abstract

In this paper, a new type of high-speed electroabsorption modulator (EAM) based on quantum dot (QD) p–i–n heterostructure is demonstrated. The QD layers sandwiched by p-AlGaAs and n-AlGaAs are grown by multilayer InGaAs self-assembled QD with luminance wavelength of 1300nm, serving as the active region of EAM. The photocurrent spectrum measurement exhibits a red shift of 15nm in QD transition energy levels on biasing from 0 to 6V. A quadratic relation of energy shift against the reversed bias is extracted, confirming the quantum-confined Stark effect (QCSE) in QD. On fabricating a 300μm long EAM, as high as DC 5dB extinction ratio by 6V voltage swing at 1310nm is observed. As compared with well-developed quantum well (QW) EAM (well thickness ∼10nm) of the same length, the lower density of states still shows the same order of magnitude in extinction ratio, suggesting strong QCSE in such 3-dimensional confined QD. An electrical-to-optical conversion with −3dB bandwidth of 3.3GHz is also attained in such QD EAM, where the speed is mainly limited by the parasitic capacitance on substrate. It implies that through optimization of QD and device structures, the advantages of QD properties are quite promising to be used in high-speed optoelectronic fields.