The Zener-Emitter: Electron injection by direct-tunneling in Ge LEDs for the on-chip Si light source

While monolithically integrated light sources for Si photonics have been investigated using Ge and GeSn on Si substrates [1-3], the challenges in material quality and efficiency remain to be solved. Turning the Group-IV material into a direct semiconductor for CMOS compatible concepts [4] promises enhanced electrical to optical conversion efficiencies. However, the red-shift in emitting wavelength is challenging for the peripheral devices such as modulators and photodetectors in complex optoelectronic integrated circuits (OEICs) [5]. We investigated a new concept by utilizing a reverse biased Ge p
⁺
n Zener diode for injection of electrons into a forward biased light emitting Ge p
⁺
-i-n diode providing holes for the radiative transition. In Ge, the direct band-to-band tunneling (BTBT) dominates over the phonon assisted indirect BTBT, which is highly beneficial for the Zener-Emitter [6]. Moreover, possible low voltage operation due to highly conductive Ge tunnel diodes and avoidance of current crowding effects by the high-energetic electron filtering mechanism of Zener diodes are further increasing the electrical injection efficiency [7].