Minority and Majority Charge Carrier Mobility in Cu2ZnSnSe4 revealed by Terahertz Spectroscopy

Hannes Hempel,Ingrid Repins,Rainer Eichberger,Charles J Hages,Thomas Unold

doi:10.1038/s41598-018-32695-6

Abstract

The mobilities of electrons and holes determine the applicability of any semiconductor, but their individual measurement remains a major challenge. Here, we show that time-resolved terahertz spectroscopy (TRTS) can distinguish the mobilities of minority and majority charge carriers independently of the doping-type and without electrical contacts. To this end, we combine the well-established determination of the sum of electron and hole mobilities from photo-induced THz absorption spectra with mobility-dependent ambipolar modeling of TRTS transients. The method is demonstrated on a polycrystalline Cu2ZnSnSe4 thin film and reveals a minority (electron) mobility of 128 cm2/V-s and a majority (hole) carrier mobility of 7 cm2/V-s in the vertical transport direction relevant for light emitting, photovoltaic and solar water splitting devices. Additionally, the TRTS analysis yields an effective bulk carrier lifetime of 4.4 ns, a surface recombination velocity of 6 * 104 cm/s and a doping concentration of ca. 1016 cm−3, thus offering the potential for contactless screen novel optoelectronic materials.

Highlights

terahertz spectroscopy (TRTS) is a widely used pump-probe technique to measure the dispersive AC-mobility μe+h(f) of photo-excited charge carriers at THz frequencies, as well as the decay of the photoconductivity from femtoseconds to nanoseconds shown in Fig. 1 1–3
In this work we address this issue by analysing TRTS
We demonstrate the determination of the sum of electron and hole mobility of the Cu2ZnSnSe4 thin film from TRTS spectra, illustrating the state-of-the-art of TRTS sum mobility measurements

Summary

Introduction

TRTS is a widely used pump-probe technique to measure the dispersive AC-mobility μe+h(f) of photo-excited charge carriers at THz frequencies, as well as the decay of the photoconductivity from femtoseconds to nanoseconds shown in Fig. 1 1–3. Transients and derive both the electron and hole mobility on the same Cu2ZnSnSe4 thin film sample.

Results

Conclusion