Influence of strain, donor concentration, carrier confinement, and dislocation density on the efficiency of luminescence of Ge-based structures on Si substrate

Electroluminescence (EL) of light-emitting diodes (LED) with different active regions and photoluminescence (PL) of Ge layers embedded in Si barriers on Si substrates has been studied. Increasing the tensile strain in the active region of Ge LEDs by using GeSn virtual substrate technology leads to an enhancement of the direct band luminescence. An intensity increase by a factor of four is achieved due to n-type doping with an antimony concentration of 3 × 1019 cm−3. The EL of LEDs with a GeSn/Ge multi quantum well structure as active region show an increased direct band luminescence of GeSn by a factor of 16 compared to an intrinsic Ge LED, revealing the advantage of carrier confinement. A high density of threading dislocations, due to the lattice mismatch of Ge and Si, causes a huge drop of PL intensity in the range of one to two orders of magnitude in the temperature range from 80 to 350 K. Thin and pseudomorphically grown Ge layers between Si barrier layers exhibit a huge PL intensity due to the absence of threading dislocations. Taking into account the thickness of the active region the direct band luminescence intensity is increased by two orders of magnitude.