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Singlet and triplet states of negatively charged excitons (trions) in ZnSe/(Zn,Be,Mg)Se quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. Singlet state binding energies, measured for different well widths ranging from 48 to 190 A, show a monotonic increase with growing magnetic fields with a tendency to saturation. This behavior is in qualitative agreement with results of model calculations. Quantitatively, the binding energy of singlet states is underestimated by about 50%. The triplet state assigned to the "dark" triplet becomes detectable in magnetic fields above 15 T. A crossover of the triplet and singlet states is expected in magnetic fields of about 50 T.

Magnetic fields applied parallel to the layer interfaces are used to study the in-plane energy dispersion and anisotropy of the two-dimensional hole subbands In valence band quantum wells. The quantum wells are formed in p-doped AIAs/GaAs/AIAs double-barrier resonant tunnelling diodes. Measurements on devices grown on (100)-oriented substrates reveal a compiicated band struciure wiin negaiive in-piane hoie effective mass for some subbands and anticrossing phenomena due to light-hole-heavy-hole coupling. Measurements have been made for quantum wells with different widths. The anisotropyofthesubbands is found to besmall forthisplane. Measurementson a device grown on a (311)A-oriented substrate reveal biaxial anisotropy in the hole subbands, some of which have a 'camel's-back'-shaped structure. The features observed experimenially are compared wiin envelope iunciion caiculations oi tile subbands of valence band quantum wells

Magnetic fields up to 41 T ( B 1 J ) are used to investigate hole tunnelling in p-type double-barrier AIAsIGaAs structures and to probe the dispersion curves of the hole states of the quantum well. The high magnetic fields reveal t h e cubic anisotropy of these states. A detailed comparison is made between the experimental data and the theoretical hole dispersion curves. Hole space charge build-up is observed in the quantum well and is measured using the Landau quantization effect for B 11 J.Recently we have demonstrated a new experimental technique, resonant magnetotunnelling spectroscopy (RMTS), for probing directly the complicated E(kll) dispersion curves of hole states in a quantum well [1,2]. The experiments are performed in a transverse magnetic field (B applied parallel to the plane of the barriers and