Disentangling nonradiative recombination processes in Ge micro-crystals on Si substrates

TL;DR

This paper investigates nonradiative recombination in Ge micro-crystals on Si, showing how surface passivation and dislocation control improve carrier lifetimes and photoluminescence efficiency at cryogenic and room temperatures.

Contribution

It demonstrates the effectiveness of GeO2 surface passivation and dislocation management in enhancing Ge micro-crystals' optical properties, providing insights into recombination pathways.

Findings

Carrier lifetimes up to 45 ns at cryogenic temperatures

Surface passivation with GeO2 improves room temperature PL emission

Dislocation management reduces nonradiative recombination

Abstract

We address nonradiative recombination pathways by leveraging surface passivation and dislocation management in micron-scale arrays of Ge crystals grown on deeply patterned Si substrates. The time decay photoluminescence (PL) at cryogenic temperatures discloses carrier lifetimes approaching 45 ns in band-gap engineered Ge micro-crystals. This investigation provides compelling information about the competitive interplay between the radiative band-edge transitions and the trapping of carriers by dislocations and free surfaces. Furthermore, an in-depth analysis of the temperature dependence of the PL, combined with capacitance data and finite difference time domain modeling, demonstrates the effectiveness of GeO2 in passivating the surface of Ge and thus in enhancing the room temperature PL emission.