Controlled epitaxy of room-temperature quantum emitters in gallium nitride

TL;DR

This work demonstrates controlled depth epitaxy of room-temperature GaN quantum emitters on silicon, enabling QE formation in a buried, well-defined layer via a silane-assisted GaN island growth followed by thick GaN overgrowth. Using MOVPE, the authors achieve QEs with high Debye-Waller factors and strong antibunching at room temperature, including $g^{(2)}(0)$ values as low as $0.26\pm0.05$ and DW factors from $0.31$ to $0.63$. Depth validation is achieved through etching and correlative imaging, showing QEs reside within the intended GaN layer above the surface treatment, and overgrowth preserves the buried emitters. The results establish a scalable GaN-on-Si route for integrating bright quantum light sources into cavities, diodes, and photonic circuits, with potential for optical and spin-based quantum technologies.

Abstract

The ability to generate quantum light at room temperature on a mature semiconductor platform opens up new possibilities for quantum technologies. Heteroepitaxial growth of gallium nitride on silicon substrates offers the opportunity to leverage existing expertise and wafer-scale manufacturing to integrate bright quantum emitters in this material within cavities, diodes, and photonic circuits. Until now, it has only been possible to grow GaN QEs at uncontrolled depths on sapphire substrates, which is disadvantageous for potential device architectures. Here, we report a method to produce GaN QEs by metal-organic vapor phase epitaxy at a controlled depth in the crystal through the application of silane treatment and subsequent growth of 3D islands. We demonstrate this process on highly technologically relevant silicon substrates, producing room-temperature QEs with a high Debye Waller factor and strongly anti-bunched emission.

Figures (4)

• Figure 1: Controlled growth of GaN quantum emitters on silicon. a) Illustration of the sample stack. b) Confocal fluorescence scan map of sample, collected in the spectral range 550 to 1000nm. c, d) Room-temperature photoluminescence spectra of a typical AlN QE in this sample and the GaN QEs, marked in b), respectively. The inset in d) is a second-order correlation measurement of QE3, marked by an asterisk in d).
• Figure 2: Emission from uncapped GaN nano-islands grown directly on the silane-treated surface. a) Illustration of the sample stack. b) Optical micrograph. c) Photoluminescence spectrum of QE4, which is highlighted in d, e). The second-order correlation of QE4 is shown in the inset. d) Atomic force micrograph image of the sample surface and e) corresponding confocal scan map. The inset in d is a smaller scale image of QE4. The white line linking some islands in d and e is provided as a guide to the eye.
• Figure 3: Patterned sample etching and mapping. a) Optical image of the etched sample surface showing a checkerboard pattern of labeled etched squares. b, c) Confocal scan maps of unetched/etched regions, respectively. d) Typical room-temperature GaN and AlN QE spectra. e) Bar chart showing the number of GaN QEs identified across all test areas. f) Depth resolved confocal scan map of QE5. The air-GaN and AlN-Si interfaces are marked with a dotted line.
• Figure 4: Microstructure of the capped sample. a) Optical micrograph of the sample after growth of a 3.0µm cap showing the presence of large voids. b) Cross-sectional transmission electron microscope image of the area around the silane-treated layer showing the presence of threading dislocations. c) Scanning capacitance microscopy phase-image of the epilayer. Darker regions illustrate the presence of n-type conductivity in the layer, most prominently in the continuous layer marking the start of 500nm GaN regrowth on the GaN-on-Si pseudo-substrate and the dark uneven layer directly above the silane treatment.