Separating density and mobility transients: Frequency-multiplexed Hall effect method

The Frequency Multiplexed Hall Effect Measurement (FMHM) enables the simultaneous measurement of charge carrier density n(t) and mobility μ(t) from resistive samples using only four electrical contacts. FMHM facilitates the study of real-time charge transport transients and time-dependent parametric conditions in Van der Pauw samples and can be implemented with a simple configuration of three independent current sources and three lock-in amplifiers. FMHM is validated within the Drude regime in three different experiments: 1) Asymmetrically contacted GaAs quantum wells (QW) demonstrate the method’s robustness; 2) AlGaN/GaN two-dimensional electron systems (2DES) show time-resolved, photo-transient responses with n(t) and µ(t) responding on different time scales; and 3) ZnInSnO (ZITO) amorphous oxide thin films exhibit a cumulative persistent photoconductivity effect whereby increases n(t) yet μ(t) remains unchanged. Additionally, parametric FMHM explores the temperature dependence of µ(T) and n(T) in bulk-doped GaAs QWs, revealing the combined effects of DX-centers and remote charge traps on QW density n(T) and their respective activation temperatures. These findings underscore FMHM's versatility in capturing dynamic charge transport phenomena across diverse materials.