Advanced Semiconductor Materials and Devices Group

Wide Band Gap Quantum Emitters

Quantum dots have been extensively studied as potential single photon sources for quantum computing. However, the use of quantum dots for quantum computing applications is hindered by various limitations, including low brightness, spectral instability, and environmental sensitivity.[1]

Therefore, in our lab we intend to explore the potential of widebandgap materials like AlN and hBN quantum emitters. They have a broad transparency window covering from ultraviolet to mid-infrared, and a significant second-order nonlinear optical effect.[2] Since they are wide-bandgap material, it makes it chemically and mechanically robust material that is stable under a wide range of environmental conditions, including temperature, humidity, and light exposure. Above and beyond, the size and shape of AlN and hBN quantum emitters can be controlled with high precision using modern nanofabrication techniques, such as electron beam lithography and dry etching. This allows for the fabrication of uniform and reproducible quantum emitters, which can lead to improved device performance and industrial scalability.

Figure 1: AlN and hBN quantum emitters exhibit a wide-bandgap, high thermal conductivity, and strong piezoelectric effects, making them highly efficient and versatile for quantum applications

AlN Quantum emitters:

In our lab we fabricate AlN epitaxial film using MBE, MOCVD system in collaboration with SSPL Delhi which has large bandgap of 6.2 eV, with a wide transparency window and a significant second-order nonlinear optical effect. This enables the AlN-based photonics devices to work in UV, visible, near-infrared (NIR) and up to MIR wavelength regime. Theoretical calculations have shown that AlN can serve as a stable environment for hosting well-isolated quantum emitters. This makes AlN quantum emitters less sensitive to external factors. Also, this property leverages its suitability for integration with existing electronic devices, such as transistors and sensors for practical applications. Apart from that, its fabrication process is monolithically compatible with CMOS fabrication line, which enables the wafer-level fabrication of AlN-based integrated photonics devices with low cost and high reliability. Compared with other semiconductor materials (e.g. Si, Ҡ = 145 W/(m·K)), AlN has significantly higher thermal conductivity (Ҡ = 285 W/(m·K)), which can help dissipate heat generated during operation, reducing the risk of thermal damage to the device. Also, AlN has small thermo-optic coefficient (dn_AlN/dT = 4.26 × 10⁻⁵/K at 1000 nm). These thermal properties make AlN-based devices able to handle high optical power since it is more tolerable to temperature fluctuations. Despite their promising characteristics, to fully harness AlN quantum emitters for quantum technologies further research is necessary to fully unlock their potential. Notably, the identification and characterization of the point defects responsible for quantum emission in AlN stand as a significant knowledge gap. Therefore, in our lab we intend to assess the potential of AlN quantum emitters in achieving high-fidelity quantum operations.

Figure 2: (a) AlN epitaxial film (1μm thick) grown over sapphire by physical vapor deposition (b) Recent review article showing AlN quantum emitters are a cutting-edge technology to create chip-scalable quantum emitters

hBN Quantum Emitters:

Hexagonal boron nitride (hBN) is a layered two-dimensional (2D) material similar to graphene. Unlike graphene, which is considered semimetal, hBN is an ultra-wide band gap semiconductor with a bandgap of ~6 eV.  Because of its high thermal and chemical stability, hBN is used as an encapsulator. Recently it has been found that hBN has luminescence emission in FUV (far ultraviolet), UV (ultraviolet), and visible range. Thus, hBN has potential applications as a light-emitting diode in the FUV region.

In our lab, we use mechanical exfoliation method to prepare hBN samples. We perform various treatment to activate defects in hBN. These defects inherit the property of 2D quantum emitters. Different characterization techniques such as Atomic Force Microscopy (AFM), Raman Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive X-Ray Analysis (EDX) have been utilized to study the morphology and chemical composition of hBN flakes.

Figure 3: Here in our lab we mechanically exfoliate the h-BN flakes from bulk and study various characterization techniques for quantum emitter applications

[1]          F. P. García de Arquer, D. V. Talapin, V. I. Klimov, Y. Arakawa, M. Bayer, and E. H. Sargent, "Semiconductor quantum dots: Technological progress and future challenges," Science, vol. 373, p. eaaz8541, 2021.

[2]          T.-J. Lu, B. Lienhard, K.-Y. Jeong, H. Moon, A. Iranmanesh, G. Grosso, et al., "Bright high-purity quantum emitters in aluminum nitride integrated photonics," ACS Photonics, vol. 7, pp. 2650-2657, 2020.