Strong Built-in Electric Field Effect Research Articles

Parameter-dependent third-order nonlinear susceptibility of parabolic InGaN/GaN quantum dots

The electron states confined in wurtzite InxGa1−xN/GaN-strained quantum dots (QDs) have been investigated in the effective-mass approximation by solving the Schrödinger equation, in which parabolic confined potential and strong built-in electric field effect due to the piezoelectricity and spontaneous polarization have been taken into account. The third-order nonlinear susceptibility of the QDs in various directions (both parallel to z direction and vertical to z direction) have been calculated, and the magnitude reaches 10−14m2/V2. It has been shown from the results that the order of the built-in electric field in the strained QD is of MV/cm. Furthermore, the results of how the third-order nonlinear susceptibility depend on the radius R of QDs, the height L of QDs, the In content x of QDs and the relaxation rate Γ10 have been given.

Interband Optical Transitions due to Donor Bound Excitons inWurtzite InGaN Strained Coupled Quantum Dots: Strong Built-in ElectricField Effects

Considering the three-dimensional confinement of the electrons and holesand the strong built-in electric field (BEF) in the wurtziteInGaN strained coupled quantum dots (QDs), the positively chargeddonor bound exciton states and interband optical transitions areinvestigated theoretically by means of a variational method. Ourcalculations indicate that the emission wavelengths sensitivelydepend on the donor position, the strong BEF, and the structureparameters of the QD system.

Hydrogenic impurity states in a wurtzite InGaN quantum dot

Within the framework of effective-mass approximation, we calculated variationally the binding energy of a hydrogenic donor impurity in a cylindrical wurtzite (WZ) InGaN/GaN strained quantum dot (QD), including the strong built-in electric field effect due to the spontaneous and piezoelectric polarizations. It is found that the donor binding energy is highly dependent on the impurity position and QD size. In particular, we found that the donor binding energy is independent of dot height when the impurity is located at the right boundary of the WZ InGaN strained QD with large dot height ( ⩾ 2.5 nm ).

Influence of the built-in electric field on luminescent properties in self-formed single In xGa 1−xN/GaN quantum dots

Based on the framework of effective-mass approximation and variational approach, luminescent properties are investigated theoretically in self-formed wurtzite In x Ga 1− x N/GaN quantum dots (QDs), considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects due to the piezoelectricity and spontaneous polarization. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the different structural parameters (the height L and the radius R) are calculated with and without the built-in electric field in detail. The results elucidate that the strong built-in electric field has a significant influence on luminescent properties of In x Ga 1− x N/GaN QDs.

Exciton states in wurtzite InGaN strained coupled quantum dots: Effects of piezoelectricity and spontaneous polarization

Within the framework of the effective-mass approximation, exciton states confined in wurtzite InxGa1−xN∕GaN strained coupled quantum dots (QDs) are investigated by means of a variational approach, including three-dimensional confinement of the electrons and holes in the QDs and strong built-in electric field effects caused by the piezoelectricity and spontaneous polarization. The relationship between exciton states and structural parameters of coupled QDs is studied in detail. We find that the strong built-in electric field in the InxGa1−xN∕GaN strained coupled QDs gives rise to a marked reduction of the effective band gap of InxGa1−xN QDs and leads to a remarkable increasing of the emission wavelengths. Both the sizes and alloy fluctuations of QDs have a significant influence on the exciton states and interband optical transitions in coupled QDs. Moreover, the barrier thickness between the two coupled InxGa1−xN QDs has a considerable influence on the exciton states and optical properties. When the barrier thickness is increased, the exciton binding energy is reduced, the emission wavelength is increased, and the electron-hole recombination rate is obviously reduced. Our theoretical results are in good agreement with the experimental measurements.

Studies of the third-order nonlinear optical susceptibility for InxGa1−xN/GaN cylinder quantum dots

The resonant third-order susceptibilities at various directions (both parallel and vertical to Z-axis) in self-assembled quantum dots (QDs) have been investigated. The nonlinear susceptibilities associated with the intraband transition in the conduction band are theoretically calculated for wurtzite InxGa1−xN/GaN-strained cylinder QDs. The confined wave functions and energies of electrons in the dots have been calculated in the effective-mass approximation by solving the 3D Schrödinger equation, in which a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization has been taken into account. Furthermore, it is shown that the magnitude and the resonant position of the nonlinear susceptibility χ(3)(3ω) strongly depend on the dots’ size as well as size distribution.

Effects of piezoelectricity and spontaneous polarization on localized excitons in self-formed InGaN quantum dots

Exciton states confined in wurtzite InxGa1−xN/GaN strained quantum dots (QDs) are investigated within the framework of effective-mass approximation and variational approach, including three-dimensional confinement of the electrons and holes in QDs and a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization. The relationship between exciton states and structural parameters of QDs is studied in detail. Our results show that the In-rich QDs-like are formed spontaneously due to In compositional fluctuations in the InxGa1−xN layer. The strong built-in electric field in InxGa1−xN/GaN strained QDs gives rise to a marked reduction of the effective band gap of QDs and leads to a remarkable electron–hole spatial separation. This effect has a strong influence on exciton states and optical properties of QDs especially for the QDs with large height (⩾5 nm) along the grown direction of the heterostructures. A good agreement has been obtained between the calculated and measured emission wavelengths for different InxGa1−xN/GaN strained QDs.

Exciton states and interband optical transitions in InGaN quantum dots

Within the framework of the effective-mass approximation, exciton states confined in wurtzite In x Ga 1− x N strained quantum dots (QDs) are investigated by means of a variational approach, including three-dimensional confinement of the electrons and holes in QDs and a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization. Our results show that the strong built-in electric field gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron–hole spatial separation. This effect has a significant influence on exciton states and optical properties of the QDs. The relationship between exciton states and height of QDs is studied. A comparison of the calculated and measured emission wavelengths for different In x Ga 1− x N QDs is given and a good agreement is obtained.