Imaging of thickness and compositional fluctuations in quantum wells by scanning capacitance microscopy
(a) Schematic diagram of a representative quantum-well structure showing contact and scanning probe measurement geometry.
Numerically simulated capacitance-voltage spectrum for a quantum-well structure.
Simulated capacitance-voltage spectra for (a) quantum well with thicknesses of plus or minus one monolayer in reverse bias, (b) quantum well with 25%, 30%, and 35% In concentration in reverse bias, (c) quantum well with 10%, 15%, and 20% In concentration in forward bias, and (d) quantum well with thickness of plus or minus one monolayer in forward bias.
(a) Topographic image and (b–d) scanning capacitance images of the quantum-well structure. Features corresponding to monolayer fluctuations in quantum-well thickness are apparent under reverse bias, but absent, as expected, under forward bias.
(a) Topographic image and (b–d) scanning capacitance images of the quantum-well structure. Bias voltages are indicated for each SCM image. Data scale is for (b), (c), and for (d). (e) SCM signal spectra extracted from images obtained at different bias voltages at points labeled A, B, and C in (d). (f) Representative single SCM signal spectrum. (g) Computed capacitance-voltage spectra for quantum-well structures with In concentrations of 10%, 20%, and 30%.
Room-temperature photoluminescence spectra for nominally identical quantum-well structures grown under conditions leading to formation of In-rich clusters (“improved”) and under conditions for which such clusters are absent (“baseline”).
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