Impact of defects on photoexcited carrier relaxation dynamics in GeSn thin films

Abstract

We report the results of a study that was conducted to investigate the recombination paths of photoexcited charge carriers in GeSn thin films. The charge carrier lifetime was predicted as a function of temperature from a description of photoconductivity transients, assuming co-influence of Shockley–Read–Hall and radiative carrier recombination paths. We identify that dislocations are the source of a band of electronic states with the highest occupied state at E V + (85÷90) meV that acts as Shockley–Read–Hall centers determining the charge carrier lifetime. The photoluminescence (PL) and photoconductivity spectroscopy have been applied to distinguish between the contribution of both band-to-band and dislocation-related electron transitions. The PL band was found to demonstrate a low-energy shift of about 80 ± 20 meV relative to the edge of the photoconductivity spectra in the indirect bandgap GeSn films with dislocations. The role of a different nature deeper acceptor level at E V + (140 ÷ 160) meV in the recombination processes of the GeSn layers with better structural quality and the Sn content higher than 4% was discussed. This detailed understanding of the recombination processes is of critical importance for developing GeSn/Ge-based optoelectronic devices.

Systematic study on photoexcited carrier dynamics related to defects in GeSn films with low Sn content at room temperature

“…This peak is significantly related to the dislocations/defects states formed in the forbidden bandgap near the GeSn/Ge interface. Previously, it has been reported that the deep defect levels existed at ∼0.55 and ∼0.62 eV for Ge 0.968 Sn 0.032 and Ge 0.96 Sn 0.04 at 83 K, respectively, which are consistent with this work [19]. Similarly, defect-related peaks were observed in GeSn with Sn contents from 1.2% to 5.0% in [39].…”

“…To deeply understand the carrier dynamic, many efforts have been conducted via the diverse methods [9,19,20]. Most experiments have been conducted at low temperature to observe the various carrier behaviors sensitively.…”

“…The nonradiative recombination in GeSn has been interpreted by three processes: (a) the SRH recombination, (b) the surface recombination, and (c) Auger recombination [9]. Also, the interface dislocations between GeSn/Ge serve as the trap states to improve the defect-related generation/recombination [19]. As such, the interpretation of carrier dynamic in GeSn films has been investigated to understand the fundamental carrier dynamic behaviors in epitaxial GeSn layers at low temperature.…”

Conductivity-Type Conversion in Self-Assembled GeSn Stripes on Ge/Si(100) under Electric Field

“…Direct-bandgap GeSn alloys are promising group-IV semiconductors for monolithic integration of light-emitting and photosensitive devices on silicon . In recent years, significant efforts have been made to produce GeSn alloys with high crystalline quality, surface morphology, optical properties, and transport properties. − Moreover, various GeSn-based optoelectronic and photonic devices such as mid-infrared photodetectors, − light-emitting diodes, and continuous-wave and pulsed lasers , have been designed and tested. Their successful design requires the realization of direct bandgap GeSn alloys due to prospects of achieving high absorptivity and high emission efficiency in the IR region.…”

High-performance GE/GESN photodetectors in near- and mid-infrared range

“…This PL peak point of 0.57 eV in Figure 74(a) is significantly related to trap states near GeSn/Ge. Previously, deep defect states were observed at 0.55 and 0.62 eV for Ge0.968Sn0.032 and Ge0.96Sn0.04 at 83 K, respectively [149]. Also, defect-related PL peaks were observed in thin GeSn films with Sn contents from 1.2 to 5.0% [150].…”