Cadmium telluride: a silicon-compatible optical material as an alternative technology for building all-optical photonic devices

ABSTRACT In this work, we report theoretical and experimental results on the use of Cadmium Telluride (CdTe) doped with Zinc (Zn) as core material for the development of all-optical photonic devices. We include the design of optical waveguides for strong field confinement, technological processes to grow CdTe on 6” or 8” wafers (suitable for high-volume manufacturing) as well as the fabrication and optical charac terization of optical waveguides with a CdTe core. Keywords: integrated optics, Cadmium Telluride, nonlinear photonics, optical waveguides. 1. INTRODUCTION Cadmium Telluride (CdTe) is a II-VI semiconductor that exhi bits an interesting optical behavior at wavelengths around 1550 nm (third optical communications window): a high index of refraction (n = 2.74), which allows for a strong confinement inside the material; a high Kerr coefficient (n 2 = 5.23x10 -13 cm 2 /W [1]), and low two-photon absorption (TPA), which can be made theoretically negligible by properly doping the material with Zinc (Zn). Thus, it seems feasible to use thin CdTe layers grown over a low-index substrate (in the same way that it is done with Silicon-on-insulator, SOI, photonics [2]) to create highly-compact all-optical devices with a nonlinear performance better than that provided by Silicon. In fact, the optical properties of the CdTe material are similar to those of Gallium Arsenide compounds, with the advantage that it could be expected that CdTe layers could be processed in an intermediate step of a CMOS manufacturing line, as it is the case of SOI-based photonics . In this work, some results on the use of CdTe as core material for the development of all-optical photonic devices are reported, including the design of waveguides for strong field confinement, technological processes to grow CdTe on 6” or 8” wafers (suitable for high-volume manufacturing) and the fabrication and optical characterizatio n of optical waveguides with a CdTe core. It has to be mentioned that idea of using CdTe as optical material for implementation of highly-dense all-optical photonic integrated circuits is intended to overcome the limitations in terms of nonlinear interaction that occurs in Silicon (mainly, the high values of TPA and the induced fr ee-carried absorption) whilst preserving the main advantages of the SOI-based photonic technology: high index contrast (small size of the photonic components) and manufacturability with CMOS tools and process (which ensures large-scale fabrication and low-cost of manufacturing).