Enhanced effect of polarization on electron transport properties in AlGaN/GaN double-heterostructure field-effect transistors

In order to understand the effect of polarization on the electron transport properties in AlGaN/GaN heterostructures, the dependence of the two-dimensional electron gas mobility on the density has been examined both in the GaN single- and 200-Å GaN double-heterostructure field-effect transistors, by means of the Hall effect measurement under the gate-voltage application at 4.2 K. In the single heterostructure, a maximum mobility of 5700 cm2/V s has been obtained at 9.0×1012 cm−2; whereas in the double heterostructure, a higher maximum mobility of 8100 cm2/V s has been obtained at a lower electron density of 6.8×1012 cm−2. The results have been analyzed in terms of potential profiles and electron distributions in both structures where both piezoelectric and spontaneous polarization effects are taken into account. The analysis has shown that the observed mobility enhancement is mainly due to the enhanced polarization-induced electron confinement in the double heterostructure and, additionally, to the improvement of the interface roughness in the structure.