Analyzing Longitudinal Magnetoresistance Asymmetry to Quantify Doping Gradients: Generalization of the van der Pauw Method

Angular phase shift in polarization-angle dependence of microwave-induced magnetoresistance oscillations

“…1(b) under B-field reversal could be due to doping gradients. 31 In the figure, we define the first (second) peak and the first valley on the positive side of B as P 1+ (P 2+) and V 1+ respectively. 19,22,[24][25][26][27] Likewise, P 1−, V 1− and P 2− are labels utilized to identify extrema on the negative side of the B axis.…”

Spatial Mapping of Local Density Variations in Two-dimensional Electron Systems Using Scanning Photoluminescence

“…The data shown here provide a direct measurement of density inhomogeneities in a high-quality GaAs 2DES. In the past, such inhomogeneities have only been inferred indirectly from transport measurements over the bulk of a device. − Similar to the nonrotated case, in Figure e, E F for the rotated sample shows noticeable local structure with random fluctuations sprinkled throughout the sample. This time, the E 0 values plotted in Figure f show very little variation across the measured area, consistent with the sample being designed to have a uniform 2DES density.…”

“…Here, we show that we have further developed this method and can now spatially map out the local 2DES density variations over macroscopic regions on the wafer with better than 100 μm precision. In contrast to earlier studies − where the average density variations were inferred from transport measurements over the entire device, our approach provides a direct and local probe of the 2DES density. We find that density fluctuations on the order of ∼10 9 electrons cm –2 exist even in high-mobility samples designed to have uniform 2DES density, which quantitatively supports some of these previous reports. , …”

“…Inspired by the fruitful outcome of such improvements to 2DES quality, endeavors to fabricate even higher quality samples continue to this day. For example, the primary source of scattering in state-of-the-art GaAs 2DESs is often attributed to background impurities, , and to this end there have been several reports on methods to purify the source material. − Another possible scattering source is the presence of density inhomogeneities within the 2DES, which have been speculated to cause unwanted effects during measurement. − However, in general electrical measurements are too global to detect these inhomogeneities. Previously, we have demonstrated the capability to measure the local 2DES density of a GaAs sample at a fixed location on the wafer using a photoluminescence (PL) technique .…”