The transport characteristics of in-plane-gated wires, in which the conducting two-dimensional electron gas (2DEG) channel and the 2DEG gates are separated by focused Ga-ion-beam scanned lines, are studied at low temperature (1.5 K). They are understood as a combination of the normal field-effect- transistor (FET) characteristics and a peculiar resistance jump at the channel pinch-off threshold. In the normal FET region, the depletion region spreading is gradually controlled by a gate voltage applied to the in-plane gates. The channel conductance variation by the gate voltage is explained by the change of the effective channel width rather than by the change of the carrier density. The variable range of the effective wire width is equal to or less than 0.6 μm in the experiments. In spite of this small controllable value, the channel can be pinched off up to W=10 μm with a gate leakage current of less than 1 nA. The pinch off of the wide wires always occurs together with a resistance jump at the threshold. These characteristics are explained by the drastic extension of the depletion region for the case that a small gate leakage occurs through the AlGaAs (Si) layer but not through the two-dimensional electron gas at the heterointerface. This resistance jump produces an interesting negative drain conductance (drain current/drain voltage) in the drain-voltage-drain- current characteristics.
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