the growth direction. This fact together with the low local Very detailed information which can be obtained expesymmetry of the interface result in an exchange (or zero rimentally was used to study in collaboration with Franz field) splitting of all four exciton sublevels. The heavy holes Ahlers and Klaus Pierz from the Physikalisch-Technische states mJ = ±3/2 couple with the ms = ±1/2 states of the Bundesanstalt in Braunschweig the influence of growth paelectron to resulting m = 2, 1, -1 and -2 exciton states. rameters on the interface quality of superlattices. In a sample In magnetic field, circularly polarized optical transitions are grown at 600C with growth interruptions of 50 seconds allowed only from the m = ±1 states. If we connect after deposition of each GaAs layer, two luminescence lines them by microwave transitions to one of the nonradiative, were observed. In the ODMR experiment it could be clearly higher populated m = ±2 states, we increase either the seen that the low energy line stems from the recombination intensity of the + or the - radiation. This shows up of an exciton with a smaller exchange splitting than that of in the circular polarization of emission and can be used the excitons contributing to the high energy line. From the to detect magnetic resonance and to examine the energy sign and shape of the level anticrossings in linear polarization level system of the excitons. Very important in this context we showed that in the low energy line only excitons localized is the fact that coupling of levels not only occurs due to at the inverted interface were observed, in the high energy microwave transitions, but also when the external magnetic line two excitons localized at both the inverted and normal field brings energy levels close to each other. Zero-field level interface were clearly separated . In this way one can crossing is the origin of the Hanle effect, which we discussed now determine in dependence of the growth parameters before. Here a level anticrossing occurs, which also effects the ratio of excitons localized at different interfaces, check level populations showing up in the intensity, circular or the physical background for that, control the quality of linear polarization of emission. Level anticrossing is a superlattices etc. It should be mentioned that the energy very helpful method of spectroscopy  since it does not levels deduced from ODMR and from the level anticrossing have the limitations of optically detected magnetic resonance resonance fields are absolutely consistent. The two different (ODMR), which usually fails for radiative lifetimes shorter exchange splittings observed for the two luminescence lines than a 0.1 µs. A systematic investigation of a large number prove the existence of regions larger than the radius of the of superlattices [12,13] reveals an approximately exponential exciton which differ in the local period and the GaAs layer dependence of the exchange splitting on the superlattice thickness by one monolayer. Obviously, the better possibility period. The isotropic exchange splitting of excitons can for relaxation of the GaAs surface by the pause during be used to determine the period of a SL. Together with growth enables the appearance of monolayer-high interface the dependence of the hole g factor on the thickness of the islands.
GaAs layer a complete geometrical characterization becomes These few examples hopefully illustrated that relations so possible with very high resolution. between Russian and German physics are in a good shape The main topic of our collaboration in the last time and that Giessen and Saint Petersburg keep the old traditions was the investigation of ODMR together with the linear vivid.
polarization of level anticrossing signals. The reason for that is the following: The sequence of layers in growth References direction differs in the orientation of the gallium respectively aluminum bonds to the arsenic atoms in the interface.
Whereas in the so-called normal (AlAs on GaAs) interface,  A. Eichenwald. Annalen der Physik 13, 919 (1904).
the AlAs bonds lie in a (110) plane, oriented along a   A. Ioffe. Vstrechi s fizikami (in Russian). Gosudarstvennoie direction, and the GaAs bonds in a (110) plane, oriented izdatelstvo fiziko-matematicheskoi literatury. Moskva (1962).
along , for the inverted interface (GaAs on AlAs) [Begegnungen mit Physikern, B.G.Teubner, Leipzig (1967)].
the situation is just opposite. This results in an inversion  W.C. Rntgen. Annalen der Physik 64, 1, 1 (1921).
Физика твердого тела, 1999, том 41, вып. From Roentgen to Ioffe, from Giessen to Saint Petersburg — Relations Between Russian and German...  W. Hanle. Z. Physik 30, 1, 93 (1924).
 Optical Orientation / Ed. by F. Meier and B.P. Zakhrchenya.
Modern Problems of Condenced Matter Physics 8. North Holland (1984).
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