Search

The polarization characteristics and intrinsic photoluminescence of M-plane GaN films on LiAl[O.sub.2] substrates were studied. The results have shown that the strain relaxation can occur in an anisotropic manner allowing for a maximum of the valence band splitting at a certain film thickness.

Using photoluminescence (PL) spectroscopy, we carry out a comparative study of the optical properties of (Ga,In)(N,As) and (Ga,In)(N,As,Sb) quantum wells. The incorporation of Sb into (Ga,In)(N,As) results in a reduced quantum efficiency at low temperatures but an improved one at room temperature (RT). A PL line shape analysis as well as the temperature dependence of the PL peak energy reveals the existence of band-tail localized states in both material systems. The carrier localization energy is larger for (Ga,In)(N,As,Sb) than for (Ga,In)(N,As), leading to a longer radiative lifetime and thus a reduced quantum efficiency at low temperatures for the former material. The thermal quenching of the quantum efficiency is analyzed by a rate equation model, which shows that the density of nonradiative centers is reduced in (Ga,In)(N,As,Sb) resulting in an enhanced quantum efficiency at RT. [ABSTRACT FROM AUTHOR]

Polarized photoluminescence spectra of M-plane GaN films grown on LiAlO2 substrates demonstrate the existence of a large polarization anisotropy in the near-band-gap excitonic transitions, which is consistent with the reduction of the in-plane crystal symmetry and the anisotropic strain generated by the lattice mismatch between GaN and LiAlO2. Band structure calculations based on the k·p formalism support the observed experimental results and allow us to explain the temperature dependence of the photoluminescence energy. From the results of these calculations and the measured excitonic transition energies, we accurately determined the in-plane strain. The strain relaxation as a function of temperature and the role of the film thickness in the in-plane strain anisotropy are also discussed. [ABSTRACT FROM AUTHOR]

The anisotropic optical properties and polarization filtering are investigated for strained M-plane GaN films as a function of the angle of the in-plane polarization vector. Since the c axis of the underlying wurtzite crystal structure lies in the film plane, its symmetry is reduced in comparison to conventional C-plane films, giving rise to an in-plane polarization anisotropy. This anisotropy is further enhanced by the anisotropic compressive in-plane strain, which occurs due to the lattice mismatch between the GaN film and the substrate LiAlO2. In addition to linear birefringence, the film also exhibits linear dichroism, resulting in a polarization filtering of an incident, linearly polarized light beam after transmission. This filtering manifests itself as a rotation of the polarization vector towards the c axis and can be as large as 80°. We compare the measured polarization rotation with calculated values taking into account the birefringence of the GaN film. In the energy range where the filtering is most effective, the birefringence almost disappears and can therefore be neglected for the determination of the rotation angle. Finally, the rotation, which is determined by the transmittance for the two orthogonal polarization directions, can be very well approximated by the product of the film thickness and the difference of the absorption coefficients for the two polarization directions. [ABSTRACT FROM AUTHOR]

We investigate the structural and optical properties of M-plane GaN(1&1macr;00) films grown on LiA1O[SUB2](100) with nucleation layers grown at high and low temperatures. Samples with a high temperature nucleation layer are found to exhibit a highly anisotropic surface morphology with pronounced corrugation, which basically replicates the surface morphology of the substrate. Photoluminescence spectra of these layers are dominated by a transition at 3.356 eV, which is absent for samples with a low-temperature nucleation layer. In conjunction with scanning electron microscopy, cathodoluminescence maps reveal that this transition predominantly stems from regions below the trenches of the surface corrugation. Transmission electron microscopy shows an abundance of stacking faults within these regions. Excitation-dependent and time-resolved photoluminescence demonstrates the intrinsic character of the 3.356 eV emission, which is thus attributed to excitons bound to stacking faults acting as ultrathin vertical quantum wells in these samples. Low-temperature nucleation is imperative to avoid thermal roughening of the substrate and thus the formation of a high density of stacking faults. [ABSTRACT FROM AUTHOR]

Measured polarization rotation is compared with calculated values taking into account the birefringence almost of the GaN film. The anisotropic optical properties and polarization filtering are investigated for strained M-plane GaN films as a function of the angle of the in-plane polarization vector.

A study was conducted to investigate the structural and optical properties of M-plane GaN(1100) films grown on LiAlO2(100) with nucleation layers grown at high and low temperatures. The result shows different optical properties of the layers, and found that this effect is linked to the generation of stacking faults at high nucleation temperature.

The anisotropic optical properties and polarization filtering are investigated for strained M-plane GaN films as a function of the angle of the in-plane polarization vector. Since the c axis of the underlying wurtzite crystal structure lies in the film plane, its symmetry is reduced in comparison to conventional C-plane films, giving rise to an in-plane polarization anisotropy. This anisotropy is further enhanced by the anisotropic compressive in-plane strain, which occurs due to the lattice mismatch between the GaN film and the substrate LiAlO2. In addition to linear birefringence, the film also exhibits linear dichroism, resulting in a polarization filtering of an incident, linearly polarized light beam after transmission. This filtering manifests itself as a rotation of the polarization vector towards the c axis and can be as large as 80°. We compare the measured polarization rotation with calculated values taking into account the birefringence of the GaN film. In the energy range where the filtering is most effective, the birefringence almost disappears and can therefore be neglected for the determination of the rotation angle. Finally, the rotation, which is determined by the transmittance for the two orthogonal polarization directions, can be very well approximated by the product of the film thickness and the difference of the absorption coefficients for the two polarization directions. [ABSTRACT FROM AUTHOR]