AlGaN/GaN high electron mobility transistors (HEMTs) are one of the most important applications of III-nitride semiconductors in modern microelectronics. They are usually produced in a planar structure on top of a GaN epilayer. High resistivity of GaN layers are prerequisite to obtain good electrical characteristics of HEMTs, especially the pinch-off effect. This can be obtained by compensation of the conductivity of as-grown layers either by defect or chemical mechanism.

In this paper we report on an attempt to obtain the carrier compensation effect in GaN by introducing controlled density of defects. It is well known that high mismatch strain leads to the nucleation of threading dislocations, dislocation loops and other defects that are produced at the substrate-layer interface. In order to be able to control defect distributions the following structure was grown using the MOCVD technique: first the thin AlN nucleation layer was grown on the sapphire substrate followed by the special buffer layer (SBL) of Al_0.4Ga_0.6N covered with high temperature GaN layer of 1 µm thickness. Since the large part of lattice strain was accommodated by the SBLs the majority of dislocations was grown at the substrate-SBL interface. Consequently, by changing the SBL thickness dislocation propagation into GaN layer can be controlled.

The produced structures were characterized by RBS/channeling and high resolution TEM and XRD techniques, which enabled the judicious choice of the SBL thickness. The ultimate proof was the properly working HEMT device produced on such a high resistivity GaN layer.

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