Magneto-Hall characterization of delta-doped pseudomorphic high electron mobility transistor structures

Abstract

Conventional Hall-effect determination of the two-dimensional electron gas (2DEG) concentration n2D in pseudomorphic high electron mobility transistor structures is invalid because of interference from the highly doped GaAs cap. Furthermore, the usual methods of dealing with this cap-interference problem, namely, (1) etching off the cap totally, (2) etching the cap until the mobility reaches a maximum, or (3) growing a separate structure with a thin, depleted cap, in general, give n2D values that are too low. However, we show here that magnetic-field-dependent Hall (M-Hall) measurements can separately determine the carrier concentrations and mobilities in the cap and 2DEG regions, as verified by comparison with a self-consistent, four-band, k⋅p calculation and also by electrochemical capacitance-voltage measurements in structures with different cap and spacer thicknesses.