ORIENTATION DEPENDENCE OF MISMATCHED INXAL1-XAS/IN0.53GA0.47AS HFETS

A device perspective is applied to the issue of critical layer thickness and the impact of strain relaxation on electrical characteristics. We have fabricated In(x)Al1-xAs/n+-In0.53Ga0.47As HFETs with InAs mole fractions in the 300 angstrom thick In(x)Al1-xAs insulator of x = 0.52 (lattice-matching), 0.48, 0.40, and 0.30. The x = 0.40 and 0.30 samples, with thicknesses greater than the critical limit, show unidirectional surface ridges that reveal misfit dislocations at the In(x)Al1-xAs/In0.53Ga0.47As hetero-interface. Dislocations are found to severely degrade the performance of devices when the current in the device flows perpendicular to them. Excellent HFETs were obtained with current flow parallel to the surface ridges for x = 0.40, in spite of the unequivocal evidence of dislocations in the devices.