The valence band structure and optical transitions of holes are investigated for elongated InGaAs/GaAs quantum dot (QD). We use the 4×4 Luttinger Hamiltonian under effective mass approximation for the estimation of the valence band structure. The energy eigenvalues and corresponding eigenvectors have been calculated by numerical diagonalization of Hamiltonian for lens-shaped QD using the harmonic oscillator basis function without considering the strain effect. We analyzed the impact of the size and composition of the QD on valence band structure and the transition probability of holes from ground state to excited states. The analysis reveals that the hole energy states form the energy band of heavy-hole (hh) and light-hole (lh) states. The band mixing of hh and lh energy states is decreasing with an increase in the lateral dimension (LD) of the QD which is indicated by the increase in the hh-lh band offset (Boff) parameter. The hh and lh states show strong intermixing for the small values of indium (In) concentration less than 0.23 and for the LD less than 10 nm for which the Boff parameter is found to be less than 25.22 meV. The widths of hh and lh bands are found to decrease with an increase in LD, and it is increasing with In concentration of the QD. The transitions from hh to hh states are polarization-sensitive, but transitions from hh to lh states are insensitive to the polarization state of the incident photon. The square optical matrix elements are decreasing with LD and increasing with In concentration.
The quantum dot light-emitting devices (QLEDs) have emerged as a promising candidate for electroluminescent devices due to their excellent optical properties, high efficiency, and tunable bandgaps. The QLEDs with increased and prolonged brightness have potential applications in lighting and display devices. However, the stability of these devices is still a matter of concern, and some factors that affect the luminescence from the device involve electric field and temperature-dependent conduction mechanism. Thermal degradation, quenching within the quantum dots, the design of charge transport layers and the charge balance between them are also some factors that affect the efficacy of these devices. The high working temperature of QLEDs is among the most challenging degradation mechanisms, thus an analysis has been carried out regarding the working temperature within the QLEDs, and the methods to minimize these effects have been studied. Another challenge is achieving charge balance within the device and different device structures have been analyzed to achieve the best results regarding charge balance within the device. A few potential strategies have been suggested to reduce the constraints faced in these electroluminescent devices.
In this study, normal incidence polarization sensitive photodetector has been proposed based on intraband transition of holes in valence band using InGaAs/GaAs quantum dots. The in-plane elongated dots have been considered for the analysis to get the polarization sensitive absorption for normal incidence of light. The dimensions of the dots and transitions are chosen such that the peak detection wavelength comes in mid-infrared spectral region. We have calculated the detector parameters such as absorption coefficient, quantum efficiency, photoconductive gain, photocurrent and dark current. The calculated absorption coefficient and photoconductive gain are found of the order of 104m-1 and 105, respectively. The impact of number of quantum dot layers on these parameters has been analyzed. We have found that increasing the number of quantum dot layers enhances the quantum efficiency and decreases the dark current of the device, but simultaneously photoconductive gain reduces drastically and because of this photocurrent of the devices also reduces. In spite of very low quantum efficiency of the photodetector with single QDs layer, it can produce a significantly high detectable photocurrent due to large photoconductive gain of the device.
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