PL spectra of the QD samples. Incorporating N into the InGaAs cap layer can redshift the QD ground state and decrease the energy separation between the ground and first-excited states. By contrast, incorporating N into the InAs QD severely degrades the intensity. The spectra due to the GaAs barrier layers and InGaAs(N) cap layers are shown in the inset. The GaAs barrier layers emit at around and the InGaAs cap layer emits at which shifts to for 0.4% N incorporation and then to for 1% N incorporation.
Temperature dependence of the PL integrated intensities of the ground states for 0%, 0.4%, and 1% N incorporation into the cap layer. The N incorporation enhances the carrier escape from the QDs when temperature increases.
characteristics of the Schottky-contact QD samples. The three samples with N incorporation showed nearly the same leakage current from . The samples with 0.4% and 1% N incorporation into the cap layer exhibited a strong current rise around but the InAsN QD sample exhibited a strong current rise at around due to a deep trap.
(a) spectra at and (b) their converted concentration profiles for the studied samples. The reference, 0.4% and 1% samples exhibited an accumulation peak but the InAsN sample showed significant carrier depletion in the QD region.
(a) Carrier profiles at several temperatures for the reference sample. The peak is attributed to electron tunneling from the QD excited states to GaAs conduction band and the shoulder is attributed to the thermal excitation from the QD ground to first-excited state; (b) carrier profiles for 0.4% N incorporation, showing the absence of the shoulder.
DLTS spectra of the QD samples. No trapping signals were visible in the reference, 0.4% and 1% N incorporation samples. However, a dominant peak around appeared in the InAsN sample.
DLTS spectra of the InAsN sample, showing the variation of the intensity of the trap for different sweeping biases from with each step of . The intensity variation suggests that this trap is located in the QD region. The rate windows are 8.6, 4.3, 2.15, and from the left to the right of the curves.
Arrhenius plots of the emission times of the trap observed in the InAsN sample. The activation energy of this trap increases from as the sweeping voltages change from . The energy position of this trap is shown in the inset.
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