G. González de la Cruz

The influence of surface segregation on the optical properties of quantum wells

Segregation of column III atoms during molecular beam epitaxy of III-V semiconductor compounds result in nonabrupt interfaces and surface compositions different from the bulk. This effect modifies the electronic states in the quantum well and the emission energy in the photoluminescence spectrum. In this work, we have solved analytically the Schrodinger equation taking into account the shape changes in the quantum well due to the segregation of atoms during the growth process of the semiconductor heterostructures. We apply this model to the case of indium segregation in the InGaAs/GaAs system. The transition energy calculations between the confined electron and hole states as function of the well width for different In composition and growth temperature are in agreement with the measured photoluminescence energy peaks.

Tunneling lifetime broadening on quantum well in an electric field

The effect of an electric field on the electron energy and resonant width in a quantum well have been investigated theoretically. By considering the tunneling of electrons under the influence of an electric field in the quantum well, we obtain a shifted and broadened energy level spectrum from the tunneling of electrons. The lifetime broadening due to the rapid tunneling escape of electrons is related to the energy width of the resonant level by the uncertainty principle. Such lifetime decreases when the electric field increases.

Electron capture by quantum wells in an internal electric field

We have investigated the electron capture times by a single quantum well, taking into account the influence of the built-in electric field due to the piezoelectric effect as in GaN/AlxGa1−xN and GaAs/InxGa1−xN structures. Theoretical carrier capture is calculated by considering a variational electron wave function inside the quantum well and a linear combination of the Airy functions above the quantum well. It is shown that the scattering rate by the optical-phonon deformation potential exhibits a smoothly decreasing function with increasing electric field. This effect is due to the shift of the bound state to lower energies and to the electron heating due to the electric field in the quantum well. This result is quantitatively in agreement with both Monte Carlo simulations and previous experimental measurements.

Tunneling effect on the intersubband optical absorption in quantum well structures

The tunneling effect on the intersubband optical absorption in a quantum well structure subjected to an external electric field perpendicular to the layers has been investigated theoretically. The analysis is based on the calculation of the intersubband transition rate by means of Fermis golden rule using expressions for the density of states, and the wave functions of the quasi-stationary energy levels inside the quantum well obtained considering the tunneling of electrons. We find that the density of states consists of peaks with asymmetrical broadening, which increase with the electric field and their positions correspond to the quasistationary levels inside the quantum well, and an expression is obtained for the intersubband absorption coefficient as a function of the photon energy. We applied these results to calculate the responsivity spectrum for a multiple quantum well infrared photodetector. The theoretical results are compared with experimental data.

Photoacoustic investigation of the effective diffusivity of two-layer semiconductors

The problem of the effective thermal diffusivity of two-layer systems is investigated using the photoacoustic spectroscopy. The experimental results are examined in terms of the effective thermal parameters of the composite system determined from a homogeneous material that produces the same physical response under an external perturbation in the detector device. It is shown that the effective thermal conductivity is not symmetric under exchange of the two layers of the composite, i.e. the effective thermal parameters depend upon which layer is illuminated in the photoacoustic experiments. Particular emphasis is given to the characterization of the interface thermal conductivity between the layer system.