Conductivity and Hall effect measurements on intentionally undoped and doped AlGaN/GaN heterostructures before and after passivation

Conductivity and Hall effect measurements were performed before and after Si3N4 passivation of intentionally undoped and doped AlGaN/GaN heterostructures on Si and SiC substrates. An increase of the sheet carrier density (up to similar to30%) and a slight decrease of the electron mobility (less than 10%) are found in all samples after passivation. The passivation induced sheet carrier density is 1.5-2x10(12) cm(-2) in undoped samples and only 0.7x10(12) cm(-2) in 5-10x10(18) cm(-3) doped samples. The decrease of the electron mobility after passivation is slightly lower in highly doped samples. The channel conductivity in both types of unpassivated samples on Si and SiC substrates increases with an increase in doping density. After passivation, a well-resolved increase of channel conductivity is observed in the undoped or lightly doped samples and nearly the same channel conductivity results in the highly doped samples. (C) 2003 American Institute of Physics.