Biaxially strained germanium crossbeam with a high-quality optical cavity for on-chip laser applications

Abstract

The creation of CMOS compatible light sources is an important step for the realization of electronic-photonic integrated circuits. An efficient CMOS-compatible light source is considered the final missing component towards achieving this goal. In this work, we present a novel crossbeam structure with an embedded optical cavity that allows both a relatively high and fairly uniform biaxial strain of ∼0.9% in addition to a high-quality factor of >4,000 simultaneously. The induced biaxial strain in the crossbeam structure can be conveniently tuned by varying geometrical factors that can be defined by conventional lithography. Comprehensive photoluminescence measurements and analyses confirmed that optical gain can be significantly improved via the combined effect of low temperature and high strain, which is supported by a three-fold reduction of the full width at half maximum of a cavity resonance at ∼1,940 nm. Our demonstration opens up the possibility of further improving the performance of germanium lasers by harnessing geometrically amplified biaxial strain.

Photoluminescence of strained germanium microbridges at various temperatures: experiment and modeling

“…High values of tensile strain were achieved both due to the geometry of the bridges and due to their cooling to low temperatures. The effect of a significant increase in the stretching of the Ge film with a decrease in temperature is also observed in locally deformed Ge structures with biaxial stretching [9]. The increase in the tensile strain in the Ge microstructures obtained by the stress concentration method with a decrease in temperature is caused by an increase and further redistribution of the tensile strain in the Ge film grown on silicon, the occurrence of which is due to the difference in the coefficients of thermal expansion Ge and Si.…”

Band lineup at hexagonal Si$_x$Ge$_{1-x}$/Si$_y$Ge$_{1-y}$ alloy interfaces

“…Various strategies to make Ge a direct-gap semiconductor, therefore suitable for Ge-on-Si optoelectronics, have been explored [4]. One favored manipulation of Ge is the application of uniaxial or biaxial strains [5][6][7][8]. Another approach is the use of hexagonal polytypes nH (n = 2, 4, 6) [9], in particular the 2H crystal structure, also called lonsdaleite, of Si [10] and Ge [11].…”

Фотолюминесценция растянутых Ge микромостиков при различных температурах: эксперимент и моделирование

“…Высокие значения деформации растяжения достигались как за счет геометрии мостиков, так и за счет их охлаждения до низких температур. Эффект значительного увеличения растяжения Ge пленки при уменьшении температуры также наблюдается и в локально деформированных Ge структурах с двуосным растяжением [9]. Увеличение деформации растяжения в Ge микроструктурах, полученных методом концентрации напряжений, при уменьшении температуры вызвано ростом и дальнейшим перераспределением деформации растяжения в пленке Ge, выращенной на кремнии, возникновение которой обусловлено разницей в коэффициентах температурного расширения Ge и Si.…”