InAs/InP Quantum Dots Grown by MOVPE Emit Broadband Telecom Single Photons Spanning 1200–1600 nm

The demand for reliable single-photon sources drives innovation in information technology, yet creating efficient devices operating within the crucial telecommunications wavelengths remains a significant challenge. Shichen Zhang, Li Liu, and Kai Guo, alongside colleagues, now demonstrate a promising solution using indium arsenide/indium phosphide quantum dots grown by a technique called MOVPE droplet epitaxy. Their research yields quantum dots that emit single photons across a broad spectral range, spanning from 1200 to 1600 nanometres, a key region for optical networks. Importantly, the team achieves a single-photon purity of 0. 16 and an exceptionally short radiative recombination lifetime of just 1. 5 nanoseconds, paving the way for future advances in integrated photonics and offering substantial potential for next-generation network applications.

InAs Quantum Dot Growth by Droplet Epitaxy

Scientists engineered a droplet-epitaxy strategy to fabricate indium arsenide and indium phosphide quantum dots, creating structures that emit light in the crucial O-band to C-band telecommunication wavelengths. This achievement supports the development of advanced information technologies by providing a source of light precisely tuned for optical communication. The team employed metal-organic vapor-phase epitaxy to carefully control the growth of these quantum dots, successfully synthesizing structures with narrow emission lines spanning from 1200 to 1600nm. Researchers investigated various growth conditions to optimize the process, ultimately achieving quantum dots with an average diameter of 48nm and a height of 12nm at a crystallization temperature of 510°C.

Profilometry confirmed minimal localized etching around the quantum dots at this temperature, ensuring structural stability and maintaining the desired shape. To encapsulate the quantum dots and fine-tune their emission wavelengths, the team deposited a thin indium phosphide capping layer, testing thicknesses of 5, 10, 15, and 20nm. Following this, the growth temperature increased to 600°C and an 80nm indium phosphide layer deposited to complete the structure and enhance its optical properties. A custom-built confocal microscopic spectroscopy system then characterized the optical properties of the resulting quantum dot samples.

This system integrated a pump laser source, a flow-type liquid helium cryostat with an objective lens, and a multi-channel data acquisition system, enabling comprehensive analysis of emission wavelength, radiative dynamics, and single-photon characteristics. Measurements performed at both room temperature and 4K using a continuous-wave laser with a 633nm excitation wavelength focused to a 1. 2μm spot size using a 0. 65 NA objective lens revealed distinct peaks attributable to the indium phosphide substrate, a 2D quasi-wetting layer formed during temperature ramping, and emission from the synthesized quantum dots.

The team observed that increasing the capping layer thickness shifted emission towards longer wavelengths, enabling detection of emission lines in the S, C, and L bands, demonstrating control over the quantum dot emission spectrum for telecommunication applications. The recorded single-photon purity of a plain quantum dot structure reached g(2)(0) = 0. 16, with a radiative recombination lifetime as short as 1. 5ns, confirming the potential of these quantum dots as efficient single-photon sources.

InAs Quantum Dots Emit Telecom-Band Photons

Scientists have achieved significant progress in developing single-photon sources for advanced information technologies, specifically targeting the crucial telecommunication bands. Detailed analysis of the growth process revealed that the synthesized quantum dots exhibit narrow emission lines, essential for precise control of photon characteristics. Atomic force microscopy measurements confirm a uniform distribution of indium droplets, with an average diameter of 45±5nm and height of 8±2nm, indicating optimized growth conditions. Following crystallization at 510°C, the resulting quantum dots demonstrate a remarkably consistent size, with a typical diameter of 48±6nm and height of 12±4nm.

The team measured a low quantum dot areal density of approximately 5×107cm−2, with localized areas exhibiting densities as low as 4×105cm−2, allowing for controlled quantum dot placement. Importantly, the quantum dots exhibit high symmetry, with an in-plane aspect ratio of 1. 06 and a standard deviation of 0. 0487, a critical factor for ideal single-photon emission. Optical characterization using a custom-built confocal microscopy system revealed distinct photoluminescence peaks.

The team recorded a single-photon purity of 0. 16, quantified by a g(2)(0) value, and a rapid radiative recombination lifetime of 1. 5ns for a single quantum dot structure. Varying the thickness of an indium phosphide capping layer, testing 5nm, 10nm, 15nm, and 20nm, allowed for fine-tuning of the emission characteristics. These results establish a crucial platform for future research focused on enhancing microcavity integration and coupling quantum dots with other photonic components within the telecommunication bands, offering significant potential for network applications.

Stable Single-Photon Sources for Quantum Networks

This research demonstrates a significant advance in the development of materials for single-photon emission, crucial for quantum technologies. Scientists successfully synthesized indium arsenide and indium phosphide quantum dots, achieving narrow emission lines spanning a broad spectral range within the telecommunications bands, specifically from 1200 to 1600 nanometers. Characterization of these quantum dots reveals a high degree of single-photon purity, with a measured g(2)(0) value of 0. 16, alongside a radiative recombination lifetime of 1. 5 nanoseconds.

The achieved results establish a robust and scalable platform for future quantum networking applications, offering compatibility with existing fiber optic infrastructure. The demonstrated stability and reproducibility of the quantum dots, produced via metal-organic vapor-phase epitaxy, address key challenges in material science for quantum information processing. While current recombination lifetimes are relatively slow, the authors anticipate significant improvements through integration with microcavity designs, potentially reducing lifetimes to the picosecond range. This work provides a reliable material foundation for advancing quantum technologies, particularly in secure communication and quantum networking, and paves the way for further integration with other photonic devices.