Temperature dependence of photoluminescence from InAs quantum dots with an asymmetric InGaAs quantum well

The dependence of the optical properties on the temperature in self-assembled InAs quantum dots (QDs) with an asymmetric InGaAs quantum well (QW) grown by using molecular beam epitaxy (MBE) was investigated with photoluminescence (PL) spectroscopy. When the InAs QDs on a 1-nm In _0.15Ga_0.85As layer were covered with an In _xGa_1-xAs layer having graded In composition from 0.25 to 0.05, the emission peak position was red-shifted with a larger energy level spacing compared to the reference QD covered by a GaAs matrix. Abnormal characteristics of the temperature-dependent PL spectra were observed. The excited-state transition for the InAs QDs with an asymmetric InGaAs QW with increasing temperature almost did not appear due to the large energy-level spacing between the ground states and the first excited states. The FWHMs of the samples with an asymmetric InGaAs QW remained nearly unchanged with increasing temperature up to 200 K and, thus, were less sensitive to temperature fluctuation. The thermal activation energy of the electron-hole emission for the InAs QDs with an asymmetric InGaAs QW was considerably decreased compared to that of the InAs QDs without the asymmetric InGaAs QW.