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A sketch illustrates the interband and intersubband transitions, intermediate levels, a two-step process ( and ), and a direct interband transition to the continuum .
Photoluminescence spectrum measured at 77 K showing to bands. The two bands are by the inset as being emission from the intermediate band and from a shallow defect.
Photoresponse spectra measured at 77 K for different bias voltages. These transitions are due to intersubband transitions in the quantum ring structure.
Photoresponse spectra measured for zero bias voltage at different temperatures showing the presence of two bands. The two-step process ( and ) and a single process are proposed to explain the two bands in the spectra.
Photocurrent and dark currents measured at room temperature as a function of bias voltage.
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