The polarisation of exciton-polariton emission is used to determine parameters of the interaction Hamiltonian of cavity polaritons. Linear polarisation of the polariton emission under linearly polarised excitation is theoretically analysed and shown to be determined by the ratio of the interaction strengths of polaritons with opposite and parallel spins. The experimentally observed inversion of the linear polarisation of the emission with respect to that of the exciting light indicates the dominant role of the exchange interaction in the polariton-polariton scattering. A comparison with the theory yields the sign of the term in the Hamiltonian describing the interaction of two polaritons with opposite spins, as well as its relative value with respect to the main term responsible for the scattering of polaritons with parallel spins.

We present a comprehensive study of longitudinal transport of two-dimensional (2D) carriers in n- and p-type modulation doped Ga(x)In(1-x)N(y)As(1-y) /GaAs quantum well structures. The Hall mobility and carrier density of electrons in the n-modulation doped quantum wells (QWs) decreases with increasing nitrogen composition. However, the mobility of the 2D holes in p-modulation doped wells is not influenced by nitrogen and it is significantly higher than that of 2D electrons in n-modulation doped material. The observed behaviour is explained in terms of increasing electron effective mass as well as enhanced N-related alloying scattering with increasing nitrogen content. In order to determine the conduction band (CB) and valence band (VB) structures as well as electron and hole effective masses, the band anticrossing model with an eight-band [Formula: see text] approximation in the Lüttinger-Kohn approach is used. The effects of strain, quantum confinement and the strong coupling between the localized nitrogen states and the CB extended states of GaInAs are considered in the calculations. The results indicate that the nitrogen induces a strong perturbation to the CB of the matrix semiconductor whilst the VB remains unaffected. The temperature dependent mobility of 2D electron gas is discussed using an analytical model that accounts for the most important scattering mechanisms. The results indicate that the interface roughness and N-related alloy scattering are the dominant mechanisms at low temperatures, while polar optical phonon and N-related alloy scattering limit mobility at high temperatures.

We report on the photoconductivity properties of devices based on ZnO nanoparticles for UV detection. The nanoparticles were synthesized by organometallic chemistry, self-assembled on Si substrates covered by inter-digited metallic electrodes and annealed at 200 • C. The photoconductivity of these devices was measured for wavelengths ranging from 300 to 600 nm. The sensitivity of our samples at 350 nm excitation wavelength is about 1 A cm 2 W −1 , or 1200 A W −1 , with a visible rejection of 150. The photoconductivity strongly depends on pressure and is one order of magnitude larger under vacuum than at atmospheric pressure. Transient photoconductivity characteristics at atmospheric pressure and under vacuum are fitted using stretched exponential functions and quantitatively analysed. These results show the potential use of chemically prepared ZnO nanoparticles for UV and/or gas detection.