Quantum photonics innovation: Silicon Nitride-integrated tunable emitters yield 94.7%. Scalable, CMOS-Compatible Heterogeneous Integration of InGaAs Quantum Dots Enables Large-Scale Quantum Circuits.

Next-generation scalable quantum photonic technologies for secure communication and quantum computation require the capacity to effortlessly merge optimised components onto a device with minimum signal loss. Jasper De Witte, Atefeh Shadmani, Zhe Liu, and others demonstrated the scalable integration of mature indium gallium arsenide (InGaAs) quantum emitters into silicon nitride (SiN) photonic circuits to overcome this basic obstacle. This development paves the way for advanced single-photon technology.

Heterogeneous integration, especially micro-transfer printing, combines high-performance quantum light sources and the low-loss SiN platform. The primary innovation is this. This technique optimises the passive photonic circuit material and quantum light source separately to maximise device performance.

Heterogeneous Integration for High Yield and Scalability

Heterogeneous integration, or hybridisation, is the best method for high yield and scalability in complex quantum circuits. SiN photonic integrated circuits (PICs) and quantum emitters are built separately before joining.

InGaAs QDs

The technology uses micro-transfer printing to precisely insert pre-characterized emitters like InGaAs quantum dots embedded in GaAs waveguides on the SiN device. By precise positioning, many quantum components and different materials can be integrated. Importantly, the scientists used readily available micro-transfer printing methods to achieve 94.7% processing yield. Scaling up functioning devices per batch and getting from proof-of-concept prototypes to mass production requires this high yield.

Monolithic integration fabrication of emitters directly within SiN material has a high integration density, but it still struggles to place good-quality emitters deterministically across large areas, making hybrid approaches better for high-yield scalability.

Silicon Nitride Benefits Due to its many advantages, silicon nitride (SiN) is the ideal photonic platform for this integration. SiN is noted for its low optical losses, which provide signal integrity and light transmission across complex photonic circuits. Since it is compatible with CMOS microelectronics, SiN photonics can use traditional industrial fabrication standards.

Waveguides on a silicon wafer are created using typical lithographic methods to make the SiN platform. While molecular beam epitaxy creates quantum dots inside GaAs membranes, they are converted into small transfer coupons.

Compatible CMOS and Electrical Control

Spectral inhomogeneity and operational noise plague solid-state quantum emitters. Researchers solved the problem by inserting integrated InGaAs quantum dots in a vertical p-i-n heterostructure.

This p-i-n arrangement locks charge states, reduces noise, and allows practically blink-free operation. Electrical biassing allows active wavelength tunability, overcoming spectrum inhomogeneity in solid-state emitters. The electrical control is compatible with ordinary CMOS technology because the bias voltages are less than 0.6V. Experimental results reveal that the integrated emitters are reliable, pure, and flicker-free after transmission.

Protecting fragile parts

The transfer technique was technologically difficult due to the tiny and delicate GaAs nanobeams, which are 160 nanometres thick and 300 nanometres wide. The researchers wrapped each nanobeam in a larger rectangular photoresist coupon to provide mechanical strength during transfer and release.

Photoresist tethers on the GaAs substrate held these coupons during release. The device design has to be changed to accommodate objective magnification and positional alignment limits while using commercial micro-transfer printing techniques to retain high coupling efficiency from the GaAs nanobeam to the SiN waveguide.

Large-Scale Quantum System Outlook

This study displays large-scale quantum photonic circuit integration. Emitters with CMOS-compatible tunability and 94.7% processing yield enable high-throughput manufacture.