Demonstration of a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>4</mml:mn></mml:math>-Cycle Phase Shift in the Radiation-Induced Oscillatory Magnetoresistance in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>GaAs</mml:mi><mml:mo>/</mml:mo><mml:mi>AlGaAs</mml:mi></mml:math>Devices

We examine the phase and the period of the radiation-induced oscillatory magnetoresistance in GaAs/AlGaAs devices utilizing in situ magnetic field calibration by electron spin resonance of diphenyl-picryl-hydrazal. The results confirm a f-independent 1/4-cycle phase shift with respect to the hf=j variant Planck's over 2pi omega(c) condition for j>/=1, and they also suggest a small ( approximately 2%) reduction in the effective mass ratio, m(*)/m, with respect to the standard value for GaAs/AlGaAs devices.