In this paper, we have made a systematic study of the electronic and optical properties of InGaN based quantum dot light emitters. The valence force field model and 6 ϫ 6k • p method have been applied to study the band structures in InGaN or InN quantum dot devices. Piezoelectric and spontaneous polarization effects are included. A comparison with InGaN quantum wells shows that InGaN quantum dots can provide better electron-hole overlap and reduce radiative lifetime. We also find that variation in dot sizes can lead to emission spectrum that can cover the whole visible light range. For high carrier density injection conditions, a self-consistent method for solving quantum dot devices is applied for better estimation of device performance. Consequences of variations in dot sizes, shapes, and composition have been studied in this paper. The results suggest that InGaN quantum dots would have superior performance in white light emitters.

It is known that conventional metal-oxide-silicon ͑MOS͒ devices will have gate tunneling related problems at very thin oxide thicknesses. Various high-dielectric-constant materials are being examined to suppress the gate currents. In this article we present theoretical results of a charge control and gate tunneling model for a ferroelectric-oxide-silicon field effect transistor and compare them to results for a conventional MOS device. The potential of high polarization charge to induce inversion without doping and high dielectric constant to suppress tunneling current is explored. The model is based on a self-consistent solution of the quantum problem and includes the ferroelectric hysteresis response self-consistently. We show that the polarization charge associated with ferroelectrics can allow greater controllability of the inversion layer charge density. Also the high dielectric constant of ferroelectrics results in greatly suppressed gate current.

We have studied the characteristics of intersubband absorption of polarized infrared (IR) radiation in as-grown and annealed self-organized InAs/GaAs quantum dots. It is observed that with the increase of annealing time and temperature, the dots tend to flatten and behave more like quantum wells. As a result, their sensitivity to TE (in-plane)-polarized light decreases and that to TM (out-of-plane)-polarized light increases. The effect could be utilized for the realization of polarization-sensitive IR detectors.

Articles you may be interested inEffects of internal strain and external pressure on electronic structures and optical transitions of self-assembled InxGa1−xAs/GaAs quantum dots: An experimental and theoretical study Combined optical and electrical studies of the effects of annealing on the intrinsic states and deep levels in a self-assembled InAs quantum-dot structure Suppression of temperature sensitivity of interband emission energy in 1.3-μm-region by an InGaAs overgrowth on self-assembled InGaAs/GaAs quantum dots In this article we examine the strain energy and intersubband optical transitions in self-assembled dots on GaAs and InP substrates. On the GaAs substrate, in addition to the InAs/GaAs dots we examine strain compensated InAs/GaAsP dots on GaAs substrates. We find that the strain energy configuration profile shows that there is preference for certain dot sizes and shapes. Our calculated dot sizes agree well with experimental observations. We find that the addition of phosphorus in the covering matrix reduces the total strain energy of the system with little effects on the intersubband transition strength for the vertical incident light. The reduced strain energy should allow one to incorporate a large number of dot array stacks for devices such as lasers and detectors and thus increases the optical responses. Our studies for the InAs/InP system show that due to the lower strain mismatch there is no particular preference for dot sizes. The optical response for intersubband transitions is weaker and occurs at longer wavelengths in comparison to the InAs/GaAs dots.

Electronic and optoelectronic properties of SiGe/Si self-assembled quantum dots are calculated by the eight-band k"p method with a revised set of parameters. The model confirms that the Si 1Ϫx Ge x transforms to a type-II structure when x is greater than 0.25 and given accurate effective masses for Si and Ge. The polarization dependent absorption spectra show a behavior quite different from what is seen in conduction band intersubband transitions in self-assembled InGaAs/GaAs dots. In-plane or x-polarized absorption increases as germanium content is increased but z-polarized absorption is highest for low germanium content. It is also shown that the z-polarized absorption can be of the same magnitude as in the x-direction by adjusting the dot composition. We also clarify how the envelope functions and the Block parts of the electronic states contribute to the absorption spectra.