Effect of heavy doping and strain on the electroluminescence of Ge-on-Si light emitting diodes

The electroluminescence of vertically emitting Ge-on-Si light emitting diodes (LEDs) was investigated for tensile strain ranging from 0% to 0.24% and for heavy n-type doping ranging from 5 × 1017 cm− 3 to 1 × 1020 cm− 3. The tensile strain increased the electroluminescence of a Ge-on-Si pin LED by a factor of 2. For high n-type doping concentrations a distinct bandgap narrowing was observed and the electroluminescence at an optimal concentration of 3 × 1019 cm− 3 increased by a factor of 5.5 compared to an undoped Ge-on-Si pin LED. In a lateral design the electroluminescence spectrum of the 4 × 1019 cm− 3 n-type doped LED shows features of high intensity and narrow linewidth.