Epitaxial Group-IV Quantum Dots as Room-Temperature Light Emitters
Authors: Spindlberger Lukas , Aberl Johannes , Murphy Armando Felipe , Fromherz Thomas , Brehm Moritz 
Published: August 2024

Next-generation Si-based applications ranging from short-range (quantum) data transfer to sensing could highly benefit from potential progress in group-IV-based telecom light emitters that can be readily implemented with Si Photonics components [1]. However, since Si is known to be an indirect band gap semiconductor, light emission is limited and inhibits the integration of efficient emitters, such as, e.g. light-emitting diodes and lasers on Si Photonic platforms.

In this presentation, we stress that a particular type of epitaxial Ge on Si quantum dots allows for overcoming the indirect bandgap limitations of Si and Ge and, thus, enables pronounced light emission even at room temperature and above [2]. These nanostructures consist of ~2 nm high Ge-rich quantum dots on Si(001) substrate epitaxially created via strain-driven formation. However, in contrast to commonly used nanostructures, we intentionally incorporate point defects into these nanostructures during their growth through in-situ low-energy Ge ion implantation [3-4]. Therefore, the point defects can be confined within the 2 nm thick Ge layer while the surrounding Si matrix remains perfectly crystalline. We will discuss the superior light-emission properties of these so-called defect-enhanced quantum dots (DEQDs) and present the current theoretical understanding of the defect’s effects on the band structure. The latter leads to the enhanced light emission from DEQDs and the opening of direct recombination channels in k-space [5,6].

In addition to signs for optically pumped lasing from DEQDs embedded in microdisk resonators, implementing these emitters into the i-region of p-i-n diodes is remarkably straightforward since the matrix material is crystalline Si [7,8]. To showcase the superior properties of these zero-dimensional light emitters, we highlight light emission from DEQD light-emitting diodes with exceptional temperature stability up to 100°C [9]. This behavior starkly contrasts conventional Si/Ge light emitters, for which the light emission is typically confined to cryogenic temperatures.

For optimizing the light emission from this interlaced defect/nanostructure complex [10], we elaborate on the testing of crucial parameters related to the temperature stability of the DEQDs [8,11], the scalability of light emission with increasing the density of the DEQDs [12] and passivation of detrimental defects in the Si matrix [13].

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[2 ] M. Brehm, Silicon Photonics IV, 67-103, Silicon Photonics IV: Innovative Frontiers, edited by David J. Lockwood and Lorenzo Pavesi, Springer series Topics in Applied Physics (2021).

[3] M. Grydlik, et al., Nano Lett. 16, 6802–6807 (2016).

[4] M. Grydlik, et al., ACS Photonics 3, 298–303 (2016).

[5] F. Murphy-Armando, et al., Physical Review B 103 (8), 085310 (2021).

[6] M. Brehm, et al., to be published

[7] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).

[8] L. Spindlberger et al., Crystals 10, 351 (2020).

[9] P. Rauter et al., ACS Photonics 5, 431-438 (2018).

[10] M. Brehm and M. Grydlik, Nanotechnology 28, 392001 (2017).

[11] L. Spindlberger et al., Physica Status Solidi (a) 216, 1900307 (2019).

[12] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).

[13] L. Spindlberger et al., Appl. Phys. Lett. 118, 083104 (2021).