Gradual evolution from quantum well like to quantum dot like characteristics in InGaAs/GaAs nanostructures
Dense arrays of carrier localizing indium-rich regions (referred to as quantum
well-dots, QWDs) formed inside an indium-depleted residual quantum well
by metalorganic vapor phase epitaxial deposition of 4–16 monolayers (ML) of
InxGa1xAs (0.3<x<0.5) on 6 misoriented GaAs (100) substrates are
studied. It is shown that in addition to QWDs the deposited layers may
contain other objects with size and shape similar to conventional selforganized
quantum dots (QDs). Transmission electron microscopy and
photoluminescence studies reveal that the density of QDs grows with the
increase in indium composition and average amount of deposited InGaAs.
The QWDs show efficient absorption in the optical region of 900–1100 nm,
whereas QDs do not contribute to photocurrent spectra and result in a waste
of carriers. Optimal indium composition x to form QWDs with high structural
and optical quality is about 0.4. For x¼0.3 the QWDs are not yet well
developed, while for x¼0.5 the density of QDs becomes too high.