The formation of two-dimensional electron gases (2DEGs) at 1 / x x Al Ga N GaN − hexagonal doublebarriers (DB) resonant tunneling diodes (RTD) is investigated by numerical self-consistent (SC) solutions of the coupled Schrödinger and Poisson equations. Spontaneous and piezoelectric effects across the material interfaces are rigorously taken into account. Conduction band profiles, band edges and corresponding envelope functions are calculated in the 1 / x x Al Ga N GaN − structures and likened to those where no polarization effects are included. The combined effect of the polarization-induced bound charge and conduction band offsets between the hexagonal AlGaN and GaN results in the formation of 2DEGs on one side of the DB and a depletion region on the other side. Using the transfer matrix formalism, the vertical transport ( J V − characteristics) in / AlGaN GaN RTDs is calculated with a fully SC calculation in the ballistic regime. Compared to standard calculations where the voltage drop along the structure is supposed to be linear, the SC method leads to strong quantitative changes in the J V − characteristics showing that the applied electric field varies significantly in the active region of the structure. The influences of the aluminum composition and the GaN ( AlGaN )thickness layers on the evolution of the current characteristics are also self-consistently investigated and discussed. We show that the electrical characteristics are very sensitive to the potential barrier due to the interplay between the potential symmetry and the barrier height and width. More interestingly, we demonstrate that the figures of merit namely the peak-to-valley ratio (PVR) of / GaN AlGaN RTDs can be optimized by increasing the quantum well width.

We present calculations of band discontinuities for Si1−xGex/Si1−yGey strained/relaxed heterointerfaces using the model-solid theory. From the obtained results, we then report a numerical simulation of the conduction-band diagram of a resonant tunneling diode in the Si/Si1−yGey system by solving self-consistently Schrödinger and Poisson equations with and without an applied electric field. An analysis of the Stark effect was made in the investigated heterostructure. Two main features have been extrapolated: (i) two sheets of a two-dimensional electron gas are created, leading to a resonant tunneling through the structure, (ii) a charge transfer can occur due to this tunneling effect. In addition, it is found that this charge transfer is highly sensitive to temperature and tends to saturate as the applied electric field increases.

Band-structure calculations are performed for cubic Al1−xGaxN using the empirical pseudopotential method. The band gaps at Γ, X and L points and the electron effective masses of Γ and X valleys are calculated as a function of the gallium fraction x. It is found that there is no significant change in these electronic band parameters on taking into account the alloy disorder. On the basis of a model solid theory, we have calculated the band discontinuities for heterointerfaces between strained Al1 −xGaxN and relaxed Al1−yGayN. The latter calculations are extended to the whole range of compositions x and y. The information derived from this investigation will be useful in the design of lattice-mismatched heterostructures in blue-light optoelectronics applications.

We report band offset calculations for lattice-matched and pseudomorphically strained In x Ga 1−x N/In y Ga 1−y N heterointerfaces using the model solid theory combined with ab initio calculations. From the results obtained, we have calculated the bandgap of bulk In x Ga 1−x N on GaN as a function of the indium composition. We have also simulated the band edges of an In x Ga 1−x N/GaN heterostructure. A self-consistent analysis is made to investigate the effect of strains on the interband transitions with the aim of achieving emissions at both visible and near infrared wavelengths. An attempt to explain the results obtained will be presented.

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