The overall aim of neaR-infrarEd resonant caVity enhancEd grAphene/siLicon photodetectors (REVEAL) is both to develop processes for the integration of graphene into a silicon (Si) technology platform and to realise high-performance Si-based photodetectors (PDs) operating at 1550 nm. Indeed, whilst the introduction of new material like graphene in a stable and reliable Si technology has to face several challenges, their use can allow overcoming the Si limitations enabling new functionalities.
Commercial Si PDs can typically operate at wavelengths below 1100 nm, however, at near-infrared (NIR) wavelengths Si become transparent and it can’t be employed anymore as active material for detection. At present, III−V compound (e.g., InGaAs, InP) and group IV (Ge) semiconductors are the materials of choice for NIR PDs, indeed commercial devices are characterized by efficiency close to the unity. The ever-growing demand and performance requirements in modern systems (such as bit-rate, number of pixels, imaging matrix size, operation and processing speed) make it crucial to integrate PDs with supporting circuitry (drivers, amplifiers, processors) on the same chip.
Since modern microelectronics relies on mature complementary metal-oxide-semiconductor (CMOS) technology, the development of NIR PDs on Si is promising for integrated microsystems, combining both optical and electronic functionalities. Unfortunately neither III-V nor Ge semiconductors are fully compatible with Si technology.
In recent years, in order to take advantage of low-cost standard Si-CMOS processing technology, the internal photoemission effect (IPE) through a metal/Si Schottky junction has been investigated. IPE is the optical excitation of electrons in the metal to energy above the Schottky barrier and then transport of these electrons to the conduction band of the semiconductor. Very recently Schottky PDs have shown increased efficiency by replacing metal with graphene, however due to the low graphene absorption (2.3%), their efficiency is still limited. In addition, the integration of graphene in a stable CMOS process is still challenging.
The aim of this project is both to develop new processes in order to integrate graphene in a reliable Si process platform and to design, fabricate and characterise a new concept of resonant cavity enhanced (RCE) graphene/Si Schottky PD operating at 1550 nm where the increased absorption at resonance wavelengths is combined with the advantages offered by the Si technology. These devices promise to compare favourably with InGaAs and/or Ge technology in term of efficiency and will represent a real breakthrough with respect to the state-of-art in the optical detection field, because they will combine high performance with CMOS compatibility at NIR wavelengths.
The proposed device is a promising candidate for various applications including: telecommunications, free space optical communications, optical coherence tomography, LIDAR, NIR imaging, remote sensing and environmental monitoring and surveillance.