Scanning spreading resistance microscopy for p – n junction and carrier distribution analysis in InGaAs/AlGaAs quantum well laser heterostructure

Scanning spreading resistance microscopy (SSRM) was used to study the spatial distribution of carrier concentration in an InGaAs/AlGaAs quantum well laser heterostructure. An analysis of the dependence of current contrast on the polarity of the applied dc bias showed that measurements should be performed at both positive and negative biases above the threshold voltage to visualize all layers of the structure. The actual position of the p–n junction can be determined by finding the point on the averaged SSRM profiles where the current signal is zero. Mathematical modeling of band diagrams and current–voltage (I–V) characteristics of p+-diamond–AlGaAs heterojunctions has shown that, regardless of the AlGaAs conductivity type, the current in the tip contact with the layers of the structure is determined not only by the layers’ conductivity but also by the height of the barrier for holes in the valence band. SSRM can be used as an effective diagnostic tool for the rapid assessment of the conductive properties of laser heterostructures, complementing other traditional analysis methods such as electrochemical capacitance–voltage profiling and secondary ion mass spectrometry.