Quantum well

About: Quantum well is a research topic. Over the lifetime, 44627 publications have been published within this topic receiving 674023 citations. The topic is also known as: QW & quantum potential well.

Spontaneous emission of localized excitons in InGaN single and multiquantum well structures

Abstract: Emission mechanisms of InGaN single quantum well blue and green light emitting diodes and multiquantum well structures were investigated by means of modulation spectroscopy. Their static electroluminescence (EL) peak was assigned to the recombination of excitons localized at certain potential minima in the quantum well. The blueshift of the EL peak caused by the increase of the driving current was explained by combined effects of the quantum‐confinement Stark effect and band filling of the localized states by excitons.

Superbright Green InGaN Single-Quantum-Well-Structure Light-Emitting Diodes

Abstract: Superbright green InGaN single quantum well (SQW) structure light-emitting diodes (LEDs) with a luminous intensity of 12 cd were fabricated The luminous intensity of these green InGaN SQW LEDs (12 cd) was about 100 times higher than that of conventional green GaP LEDs (01 cd) The output power, the external quantum efficiency, the peak wavelength and the full width at half-maximum of green SQW LEDs were 3 mW, 63%, 520 nm and 30 nm, respectively, at a forward current of 20 mA The p-AlGaN/InGaN/n-GaN structure of green InGaN SQW LEDs were grown by metalorganic chemical vapor deposition on sapphire subsutrates

Gain and the threshold of three-dimensional quantum-box lasers

Abstract: Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 A × 100 A × 100 A GaAs/Ga 0.8 Al 0.2 As quantum box, and 15 times for Ga 0.47 In 0.53 As/InP quantum box with the same size, respectively. The threshold current density are 45 A/cm2and 62 A/cm2for GRINSCH GaAs/(Ga 0.8 Al 0.2 As-Ga 0.4 Al 0.6 As) and Ga 0.47 In 0.53 As/(Ga 0.28 In 0.72 As 0.6 P 0.4 -InP), respectively, where for the GaInAs/ GaInAsP/InP system the intervalence band absorption and nonradiative recombinations have been assumed to be the same as those obtained for bulk crystals experimentally. These results show the possibility of remarkable reduction in the laser threshold by the quantum-box structures.

Pyroelectric properties of Al(In)GaN/GaN hetero- and quantum well structures

Abstract: The macroscopic nonlinear pyroelectric polarization of wurtzite AlxGa1-xN, InxGa1-xN and AlxIn1-xN ternary compounds (large spontaneous polarization and piezoelectric coupling) dramatically affects the optical and electrical properties of multilayered Al(In)GaN/GaN hetero-, nanostructures and devices, due to the huge built-in electrostatic fields and bound interface charges caused by gradients in polarization at surfaces and heterointerfaces. Models of polarization-induced effects in GaN-based devices so far have assumed that polarization in ternary nitride alloys can be calculated by a linear interpolation between the limiting values of the binary compounds. We present theoretical and experimental evidence that the macroscopic polarization in nitride alloys is a nonlinear function of strain and composition. We have applied these results to interpret experimental data obtained in a number of InGaN/GaN quantum wells?(QWs) as well as AlInN/GaN and AlGaN/GaN transistor structures. We find that the discrepancies between experiment and ab initio theory present so far are almost completely eliminated for the AlGaN/GaN-based heterostructures when the nonlinearity of polarization is accounted for. The realization of undoped lattice-matched AlInN/GaN heterostructures further allows us to prove the existence of a gradient in spontaneous polarization by the experimental observation of two-dimensional electron gases?(2DEGs). The confinement of 2DEGs in InGaN/GaN QWs in combination with the measured Stark shift of excitonic recombination is used to determine the polarization-induced electric fields in nanostructures. To facilitate inclusion of the predicted nonlinear polarization in future simulations, we give an explicit prescription to calculate polarization-induced electric fields and bound interface charges for arbitrary composition in each of the ternary III-N alloys. In addition, the theoretical and experimental results presented here allow a detailed comparison of the predicted electric fields and bound interface charges with the measured Stark shift and the sheet carrier concentration of polarization-induced 2DEGs. This comparison provides an insight into the reliability of the calculated nonlinear piezoelectric and spontaneous polarization of group III nitride ternary alloys.

Recent developments in thermoelectric materials

Abstract: Efficient solid state energy conversion based on the Peltier effect for cooling and the Seebeck effect for power generation calls for materials with high electrical conductivity σ, high Seebeck coefficient S, and low thermal conductivity k. Identifying materials with a high thermoelectric figure of merit Z(= S2σ/k) has proven to be an extremely challenging task. After 30 years of slow progress, thermoelectric materials research experienced a resurgence, inspired by the developments of new concepts and theories to engineer electron and phonon transport in both nanostructures and bulk materials. This review provides a critical summary of some recent developments of new concepts and new materials. In nanostructures, quantum and classical size effects provide opportunities to tailor the electron and phonon transport through structural engineering. Quantum wells, superlattices, quantum wires, and quantum dots have been employed to change the band structure, energy levels, and density of states of elect...