Influence of strain relaxation of the Al[sub x]Ga[sub 1-x]N barrier on transport properties of the two-dimensional electron gas in modulation-doped Al[sub x]Ga[sub 1-x]N/GaN heterostructures.

Influences of the thickness of the Si-doped n-type Al[sub 0.22]Ga[sub 0.78]N barrier and the thickness of the Al[sub 0.22]Ga[sub 0.78]N spacer on mobility and density of the two dimensional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures were investigated. 2DEG mobilities of 1274 cm2/V s at 300 K and 4495 cm2/V s at 77 K were reached. Both 2DEG mobility and density decrease dramatically when the Al[sub 0.22]Ga[sub 0.78]N barrier becomes partially relaxed, indicating that transport properties of the 2DEG are influenced significantly by the piezoelectric polarization of the Al[sub 0.22]Ga[sub 0.78]N layer. From our results, the critical thickness of an Al[sub 0.22]Ga[sub 0.78]N layer on GaN is estimated to be between 65 and 75 nm, which is much higher than that predicted by theoretical calculation. This may be attributed to the interaction of misfit dislocations and the presence of a high density of extended defects in the Al[sub 0.22]Ga[sub 0.78]N layer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]