The quantum confined Stark effect in InAs/InGaAs QDs using an undoped and p-modulation doped active region was investigated. Doping potentially offers more than a 3x increase in figure of merit modulator performance up to 100 °C.
Results of heat-capacity and resistivity measurements performed on PrAl3 between 1.5 and 300 K are utilized to reveal and characterize the influence of the crystalline electric field on the ground-state multiplet of Pr+3 in PrAl3. Also reported are the results of heat-capacity measurements on the isostructural nonmagnetic counterpart LaAl3 for which there are only vibrational and electronic contributions to Cp. Below 180 K, the excess heat capacity of PrAl3 over that of LaAl3 exhibits of Schottky-type thermal anomaly peaking at 25 K and is attributable to excitation within the crystal-field states. Resistivity results indicate a temperature-dependent spin-disorder contribution at low temperatures associated with the splitting of the ground-state multiplet by the crystal field. The higher-temperature resistivity behavior is observed to be a linear function of temperature and can be readily assigned to phonon contribution. The crystal-field interaction is analyzed using the crystal-field Hamiltonian, HCF=W246 (1 − |y|)O2/F2 + y[xO4/F4 + (1 − |x|)O6/F6], which incorporates a second-order term to account for the nonideal crystallographic c/a ratio exhibited by PrAl3. Best agreement between experimental and calculated heat capacity, resistivity, and susceptibility was obtained using the parameters x=−0.60 and y=0.65 with a positive value of W246. A singlet ground state results with an over-all splitting of the crystal-field levels of 132 K. The parameters x and y are in reasonable agreement with calculations based on the point-charge model.
The quantum-confined Stark effect in InAs/In(Ga)As quantum dots (QDs) using non-intentionally doped and p-doped QD barriers was investigated to compare their performance for use in optical modulators. The measurements indicate that the doped QD barriers lead to a better figure of merit (FoM), defined as the ratio of the change in absorption Δα for a reverse bias voltage swing to the loss at 1 V α(1 V), FoM=Δα/α (1 V). The improved performance is due to the absence of the ground-state absorption peak and an additional component to the Stark shift. Measurements indicate that p-doping the QD barriers can lead to more than a 3x increase in FoM modulator performance between temperatures of −73 °C to 100 °C when compared with the stack with NID QD barriers.
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