We study the four-terminal resistance fluctuations of mesoscopic samples near the transition between the nu=2 and the nu=1 quantum Hall states. We observe near-perfect correlations between the fluctuations of the longitudinal and Hall components of the resistance. These correlated fluctuations appear in a magnetic-field range for which the two-terminal resistance of the samples is quantized. We discuss these findings in light of edge-state transport models of the quantum Hall effect. We also show that our results lead to an ambiguity in the determination of the width of quantum Hall transitions.

The symmetry properties of the resistance of mesoscopic samples in the quantum Hall regime are investigated. In addition to the reciprocity relation, our samples obey new symmetries, that relate resistances measured with different contact configurations. Different kinds of symmetries are identified, depending on whether the magnetic field value is such that the system is above, or below, a quantum Hall transition. Related symmetries have recently been reported for macroscopic samples in the quantum Hall regime by Ponomarenko et al. (Solid State Commun. 130, 705 (2004)), and Karmakar et al. (Preprint cond-mat/0309694).

We fabricated top gate TFTs of microcrystalline silicon (μc-Si) deposited at 360 °C. The TFTs have field-effect electron mobilities of up to 7.9 cm2/Vs in the saturation regime and 5.8 cm2/Vs in the linear regime. The highest ION/IOFF ratio is 105. Typical values for Vth is 6.5 V and for the subthreshold slope is 1.7 V/decade. The μc-Si is grown by PE-CVD from a source gas mixture of SiH4, SiF4 and H2, with a typical flow ratio of 1:20:200, at a pressure of 120 Pa and a power density of 160 mW/cm2. The TFT structure is built on un-passivated Coming 7059 glass, with 300 n+ μc-Si, 60 nm n+ μc-Si source and drain contact layers, 200 nm SiO2 or 300 nm SiNx gate insulator, and 100 nm Al gate, source and drain electrodes.

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We present an experimental study of four-terminal resistance fluctuations of mesoscopic samples in the quantum Hall regime. We show that in the vicinity of integer quantum Hall transitions there exist two kinds of correlations between the longitudinal and Hall resistances of the samples, one on either side of the transition region.