Evaluation of electronic transport properties and conduction band offsets of asymmetric InAs/InxGa1-xAs/GaAs dot-in-well structures

The charge carrier distribution profile, carrier dynamics, barrier height and conduction band offset for asymmetric InAs/InxGa1-xAs/GaAs dot-in-well (DWELL) structures are evaluated from temperature-dependent electronic transport and spectroscopic measurements. The charge carrier leakages via defects lead to less charge carrier accumulation in the DWELL architecture in comparison with the associated QWs. Furthermore, the differential capacitance-voltage measurements show the resonance of charge carrier escape rate with the ground and excited states of the DWELL structure. The peak of the charge carrier escape rate related to the excited state is almost independent of the temperature while that of the ground state changes significantly with heating. It is explained on the basis of changes in the accumulated carrier density due to carrier localization and nonradiative recombination processes, via defects/dislocations/Auger recombination, which are dominant at moderate and high temperatures, respectively. Furthermore, the obtained values of barrier height and conduction band offsets for asymmetric InAs/InxGa1-xAs/GaAs (x = 0.18) DWELL structures are 194 +/- 10 meV and 287 +/- 10 meV, respectively. Downward transitions from both ground and excited states of quantum dots (QDs) are observed in photoluminescence while upward transitions only to the excited state energy levels of QDs are observed in photoreflectance spectroscopy. This is due to the filling of the ground state energy levels of QDs, which is confirmed by the electron transport measurements. Hence, it is concluded that interband absorption occurs to the excited states, whereas intersubband absorption predominantly takes place from the ground states to the continuum of the QD ensemble.