Direct-bandgap luminescence at room-temperature from highly-strained Germanium nanocrystals

Abstract

Efficient room-temperature luminescence at optical telecommunication wavelengths and originating from direct band-to-band recombination has been observed in tensile-strained germanium nanocrystals synthesized by mechanical grinding techniques. Selected area electron diffraction, micro-Raman and optical-absorption spectroscopy measurements indicate high tensile-strains while combined photoluminescence spectroscopy, excitation-power evolution and time-resolved measurements suggest direct band-to-band recombination. Such band-engineered germanium nanocrystals offer great possibilities for silicon-photonics integration due to their superb light-emission properties, facile fabrication and compatibility with standard microelectronic processes.

Bandgap-customizable germanium using lithographically determined biaxial tensile strain for silicon-compatible optoelectronics

“…The structures characterized by PL had a 11 relatively large inner microdisk diameter of 7.5 µm to accommodate the finite spot size of the excitation laser, and the use of substrate-adhered Ge structures in this work precludes any significant heating effects from the 12 mW laser excitation 20 . Biaxial strain is well understood to enhance Ge luminescence by increasing the fraction of electrons in the direct conduction valley 5,17,23,31,32 , and we observe this phenomenon in our PL measurements. As shown explicitly in the inset of Figure 5b, the integrated intensity of the PL emission from our Ge structures increases by a factor of ~2.3x as the strain increases from zero to 0.98%.…”

Formation and characterization of varied size germanium nanocrystals by electron microscopy, Raman spectroscopy, and photoluminescence

“…According to Nataraj et al [19], the Ge ncs Raman peak shifts its position linearly with the excitation power density due to the thermal effect. Special attention should be paid to the nanocrystals because their Raman signal usually is weak.…”

“…The emission wavelengths can also be tuned between 1548 nm and 1905 nm by changing the doping levels [13]. Ge ncs were reported to emit between 563 nm and 1548 nm explained by the quantum confinement effect (QCE) [15][16][17][18][19][20][21]. In addition, many results have been published covering the entire visible and ultraviolet (UV) ranges related to various defects or interface of Ge ncs with matrix [18,[22][23][24][25][26][27].…”

Size-effect of germanium nanocrystals

“…According to Nataraj et al [3], the Ge ncs Raman peak shifts linearly with the excitation power density due to the thermal effect. Special attention had been paid to nanocrystals because the Raman signal usually is weak.…”