Excitons and excitonic complexes in GaAs/AlGaAs quantum wells with a low-density quasi-two-dimensional electron and hole channel

The recombination spectra of excitons and excitonic complexes in un-doped GaAs/AlGaAs single quantum wells are investigated. It is shown on the basis of a study of the magnetic-field dependence of the emission spectra and the degree of optical orientation in zero magnetic field and on the basis of electrooptic measurements that not only the density but also the sign of the charge carriers in a well depend strongly on the photoexcitation energy. It is shown on the basis of a comparative analysis of the spin splitting of the recombination lines of free and bound excitons that the recombination line which was attributed earlier to a positively charged exciton corresponds to the recombination of an exciton bound on a neutral acceptor. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 707–713 (10 May 1998)     

Free and localized positively charged excitons in the emission spectrum of GaAs/AlGaAs quantum wells

The recombination emission spectra of an excitonic complex (A ⁰ X) localized on a neutral acceptor, which have previously been attributed to a positively charged exciton (X ⁺), are investigated. Satellites arising around the main luminescence line as a result of recoil processes during recombination of the complex which leave the surviving hole in an excited state are observed and investigated. It is shown in a computational model based on the Luttinger Hamiltonian that the energy splittings between the main line and the satellites correspond to an in-barrier impurity center located a definite distance from the well. It is shown that as the magnetic field increases, a transition is observed from the singlet ground state of the complex to a multiplet state. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 223–228 (10 August 1998)     

Evidence for Coulomb staircase in tunneling through an antidot island in the quantum Hall regime

We studied the – characteristics of tunneling devices, defined by two trench fingers and an antidot island patterned on Corbino rings in the quantum Hall plateau regime. Well-developed current steps were observed at filling factors near , which we interpret as a Coulomb staircase phenomenon due to charging of compressible strips around the antidot. The evolution of the current steps with filling factor is explained in the quasi-elastic inter landau level scattering model.     

Intersubband collective excitations in a quasi-two-dimensional electron system in external magnetic field

The spectrum of collective excitations in a quasi-two-dimensional electron system was studied by the method of Raman scattering spectroscopy. In an applied magnetic field, such systems exhibit collective excitations related to the electron transitions between dimensionally quantized subbands with a change in the Landau level index (intersubband Bernstein modes). It is shown that these modes interact with the fundamental intersubband excitations of the charge and spin densities, the interaction energy being determined by the excitation quasimomentum. Interaction of the intersubband Bernstein modes and the fundamental intersubband excitations with quasi-two-dimensional LO phonons was studied. Behavior of the new branches of collective excitations in a quasi-two-dimensional electron system possessing more than one occupied Landau level was studied and the nature of these branches was determined.     

Evidence of surface charge at the air/water interface from thin-film studies on polyelectrolyte-coated substrates

The stability of thin water films on silicon substrates coated with cationic and anionic polyelectrolytes was investigated by the thin film pressure balance technique. Depending on the surface charge of the substrate, the water films are either stable (on negatively charged wafers) or rupture rapidly (on positively charged wafers). It is supposed that this behavior is due to a negative surface charge of the free water surface. The underlying assumption that the films' stability is due to electrostatic interactions is supported by measurements of the disjoining pressure on silicon wafers with a native oxide layer, which indicates a decrease of the film thickness, and thus decreasing repulsive interaction between the two film interfaces, with increasing ionic strength.