Observation of subsurface monolayer thickness fluctuations in InGaN/GaN quantum wells by scanning capacitance microscopy and spectroscopy

摘要

Scanning capacitance microscopy and spectroscopy combined with numerical simulations have been used to image nanoscale electronic structures in In_(0.30)Ga_(0.70)N/GaN quantum-well heterostructures grown by metalorganic chemical vapor deposition. Macroscopic capacitance-voltage spectroscopy and numerical simulations indicate that, depending on the bias voltage applied, either electron or hole accumulation in the n-type quantum-well region can occur. Scanning capacitance microscope images reveal local variations in electronic properties with structure similar to that of monoatomic steps observable in surface topography. Scanning capacitance spectroscopy combined with numerical simulations indicates that the observed features correspond to variations in carrier concentration arising from monolayer fluctuations in the thickness of the subsurface In_(0.30)Ga_(0.70)N quantum-well layer, with thickness variations occurring over distances of tens of nanometers to a micron or more.