Modern microelectronics are predominantly made from silicon materials. This supremacy has been facilitated by the field-effect transistor and the related complementary-metal-oxide-semiconductor (CMOS) technology. Consequently, the field of silicon photonics has spawned, with the grand aim of seamless integration of all electronic and photonic functions on the same CMOS platform. Most of the basic building blocks toward this goal are already widely available; nonetheless, one major shortfall remains: i.e. integrating a light source on a silicon chip in an efficient and industrially viable way. In particular, light sources based on direct heteroepitaxy on silicon would be beneficial. At present, existing literature has shown that instead of direct heteroepitaxy, the available established way of light generation in silicon photonics is through the so-called hybrid-laser integration. In general, the ultimate target for silicon photonics is to merge together all electronic and photonic functions on the same CMOS platform. This requires efficient light emitters and absorbers directly integrated on silicon chips, the lack of which presently forms one of the major bottlenecks for further progress.
III–V nanowires have been studied for more than two decades where research has shown that they do not require lattice matching with the substrate to achieve good crystal quality. Unfortunately, electrical injection remains challenging using the conventional method, where first, the nanowires require p-n junctions and second, need to be contacted from the top using somewhat complicated methods and materials prone to absorbing part of the emitted light. On this account, Dr. Pyry Kivisaari at the Engineered Nanosystems (ENS) Group at Aalto University in Finland proposed a new solution by combining diffusion-driven charge transport (DDCT), lateral doping of silicon, and III–V nanowire growth to create fully integrated near-surface light emitters and absorbers controlled solely by biasing the underlying silicon wafer. His work is currently published in the research journal, Physical Review Applied.
Dr. Pyry Kivisaari carried out simulations to show that combined with the remarkable diffusion lengths in silicon and existing lateral-doping techniques, could offer a path toward fully silicon-integrated electrically injected free-standing nanowire light emitters and absorbers.
The author reported that based on the three-dimensional full-device simulations carried out, DDCT was seen to enable high efficiencies for both light emission and photodiode operation in technically feasible silicon-integrated free-standing nanowire structures. Moreover, results indicated that DDCT was especially well suited for the commonly used 1.55μm wavelength due to the optimal band-gap difference with silicon, which promotes both a high injection efficiency and low voltage losses.
In summary, the study reported on full-device simulations of free-standing III–V nanowires on laterally doped silicon. The goal was to assess their feasibility as directly integrated light emitters and absorbers for silicon photonics. Overall, the results presented were impeccable and founded on solid fundamental principles of charge carrier transport in semiconductors and the ENS group’s previous experimental results. In a statement to Advances in Engineering, Dr. Pyry Kivisaari highlighted that the promising results got him extremely excited to continue working towards the first experimental prototypes of the structures and, hopefully later, to develop the concept to full optical on-chip communication links and other potential new device applications.
Pyry Kivisaari. Silicon-Integrated III–V Light Emitters and Absorbers Using Bipolar Diffusion. Physical Review Applied, volume 13, 064035.