Vertical electro-absorption modulator design and its integration in a VCSEL

International audienceElectro-absorption modulators, either embedded in CMOS technology or integrated with a semiconductor laser, are of high interest for many applications such as optical communications, signal processing and 3D imaging. Recently, the integration of a surface-normal electro-absorption modulator into a vertical-cavity surface-emitting laser has been considered. In this paper we implement a simple quantum well electro-absorption model and design and optimize an asymmetric Fabry–Pérot semiconductor modulator while considering all physical properties within figures of merit. We also extend this model to account for the impact of temperature on the different parameters involved in the calculation of the absorption, such as refractive indices and exciton transition broadening. Two types of vertical modulator structures have been fabricated and experimentally characterized by reflectivity and photocurrent measurements demonstrating a very good agreement with our model. Finally, preliminary results of an electro-absorption modulator vertically integrated with a vertical-cavity surface-emitting laser device are presented, showing good modulation performances required for high speed communications

In-situ magnification inferred curvature measurement applied to dilute bismide growth

International audienceProbing in real time thin film processes is an efficient way to unravel the impact of key parameters as this approach offers a direct insight on the involved mechanisms. MBE has benefited from a large number of in-situ techniques like RHEED, reflectivity, or optical thermometry. Despite the direct measurement of stress in the growing layers that they allow, curvature measurement tools based on laser deflectometry have not been widely adopted by the MBE community, due to intrinsic technological limitations. We have developed a novel curvature measurement technique, named Magnification Inferred Curvature (MIC), that overcomes these limitations. We will explain the principle of the measurement and illustrate its unique capabilities with a few selected examples, focusing on the GaAs1-xBix alloy. Keywords: in-situ, curvature, stress, dilute bismid

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

International audienceIn this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green's function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm−2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors