Fabrication and evaluation of SiC optical modulators

Abstract

Silicon Carbide is a potentially useful compound for use in silicon based photonics because cubic silicon carbide (3C-SiC), possesses a first order electro-optic (Pockels) effect, something absent in pure silicon. This means the material is potentially suitable for high speed optical modulation. Furthermore, the wide bandgap (2.2 eV) of 3C-SiC makes the devices suitable for use over the visible and near infrared spectrum range as well as the longer communication wavelengths, and also means the material can tolerate high temperatures. However, relatively little work has been carried out in SiC for photonics applications. In this paper we will discuss design and fabrication of both SiC waveguides and modulators for silicon based photonics. The fabrication process utilises ion implantation of oxygen into SiC to form the lower waveguide boundary. Subsequently, ribs are etched and contacts are added to form the optical modulators. Consideration of both Pockels modulators and plasma dispersion modulators has been made, and both will be discussed here. These devices have potential for optical modulation, but are also compatible with silicon processing technology.We have demonstrated waveguiding in 3C-SiC, established a processing recipe for the SiC wafers which enables fabrication of 3-dimensional devices, and demonstrated optical modulation. Performance of the resultant devices is compared to other silicon based devices in terms of operating speed and efficiency.Keywords: Si-based optoelectronics, silicon on insulator, SiC planar waveguides, SiC rib waveguides, modulators (DWDM). Since the linear electro-optic effect (Pockels effect) is not present in crystalline silicon due to the centrosymmetric crystal structure, active devices such as modulators and switches must be designed using the free carrier dispersion effect [1]. Furthermore, the transparent wavelength range of Si is limited to the region of above l.2jtm, and therefore applications in the visible wavelength range are excluded. There is a great demand for photonic integrated devices compatible with silicon technology and the use of silicon based alloys (SiGe, SiGeC, SiC) offer a solution for some applications.SiC has been considered for high-power and high-temperature devices because of its attractive electronic properties. The cubic polytype (3C or ) of the silicon carbide (SiC) has a wide bandgap (2.2eV), it is transparent in the range O.54-2tm and therefore suitable for waveguiding over the visible and near-infrared wavelength range as well as the longer communication wavelengths. f3-SiC is a crystal with a zincblende structure and possesses a 43m point-group lattice structure which is non-centrosymmetric. Hence the electro-optic effect is observable, and the electro-optic coefficient is more than 70% higher than that of GaAs [2]. Optical devices fabricated from fE-SiC can be operated in the visible range, *

Integrated silicon carbide electro-optic modulator

“…Consequently, Pockels-based modulators are exploited to achieve high data rates and microwave-conversion efficiencies without the addition of optical loss 10 and are foundational to many applications 11 . Despite the discovery of the Pockels effect in bulk cubic SiC (3C-SiC) more than three decades ago 12 , an integrated electro-optic modulator has yet to be realized in SiC for a number of reasons including poor crystal quality and difficulty realizing low-loss waveguides [13][14][15][16] . Although 3C-SiC can be grown directly onto a silicon substrate, it has been difficult to obtain high-quality thin films due to crystal defects associated with this approach 7,17,18 .…”

Racetrack microresonator based electro-optic phase shifters on a 3C silicon-carbide-on-insulator platform

“…Bulk 3C-SiC crystals demonstrate the EO effect with an EO coefficient r41 of 2.7 pm/V [28] that can enable the modulation of the phase of an optical wave in a photonic waveguide by applying an electric field. Previously, the 3C-SiC EO modulators have been studied both  Corresponding email: ali.adibi@ece.gatech.edu numerically in the integrated form [29] and experimentally in the nonfully integrated form [30]. A major challenge in the experimental demonstration of fully-integrated SiC EO devices with practical performance measures has been the lack of a high-quality SiC integrated-photonic platform.…”

Integrated silicon carbide modulator for CMOS photonics

“…Moreover, the wide bandgap of SiC allows broadband optical transparency from ultraviolet to infrared. Despite this, a SiC-based Pockels modulator has not been experimentally demonstrated due to poor crystal quality and difficulty obtaining low-loss waveguides [20][21][22][23] . Although 3C-SiC can be grown directly onto a silicon substrate, it has been difficult to realize high-quality thin films, due to crystal defects associated with this approach 23,24 .…”