H. Priller

Electrical and optical properties of the CdS quantum wells of CdS/ZnSe heterostructures

Earlier we reported the investigation of the electrical properties of selectively doped and degenerate CdS/ZnSe quantum heterostructures grown by molecular beam epitaxy [V. Kažukauskas, M. Grun, St. Petillon, A. Storzum, and C. Klingshirn, Appl. Phys. Lett. 74, 395 (1999)]. The maximum Hall mobilities in these heterostructures were found to be less than 400 cm2/Vs. In the present work we analyze in detail the scattering mechanisms in order to increase the carrier mobility and to optimize these quantum structures. We demonstrate that the Hall mobility can reach in the CdS quantum wells at low temperatures 2800 cm2/V s for slightly doped structures, having an effective sheet carrier density 2.6×1011 cm−2. In these structures the mobility is mostly limited by interface alloying scattering. At high doping levels carriers become redistributed between the quantum well and the ZnSe doped layer. This causes the parallel conductivity phenomena, which diminishes the effective mobility. Near room temperature the sca...

High Excitation Effects and Relaxation Dynamics in CdS/ZnSe Single Quantum Wells

Photoluminescence of the ground and excited states of type II CdS/ZnSe single quantum wells with different width is investigated for high electron densities and by means of time resolved photoluminescence measurements. For high excitation intensities the filling of states in the QW up to energies of the second excited state can be observed. The PL decay times of the ground state vary from 2-36 ns for different samples and depend strongly on the QW width. This dependence can be explained with the overlap of electron and hole wavefunctions. The PL rise time of the ground state is influenced by inter- and intrasubband relaxation, which is induced by the cooling of hot carriers.

Processes of Stimulated Emission in ZnO

In this contribution we present a critical review of experimental data and theoretical considerations concerning the stimulated emission in ZnO. The main processes discussed in literature leading to stimulated emission at RT are inelastic exciton‐exciton scattering (P‐band) and recombination of an inverted band‐to‐band transition in an electron‐hole plasma (EHP). While the latter process becomes dominant at RT for densities close to 1019 cm−3 theory predicts a lower threshold for inelastic exciton‐free carrier scattering compared to the P‐band. In addition to that the exciton‐nLO phonon process might also have a lower threshold than the P‐band. A detailed analysis of the temperature dependence of the band gap and of the homogenous broadening of the exciton resonance allows us to distinguish between the various processes but also casts some doubt on the frequently given claim of excitonic RT lasing in ZnO. Therefore we argue that inelastic scattering processes with carriers, phonons or plasmons in a still ...

Temperature dependent dynamics of the excitonic photoluminescence in zinc oxide nanorods

The temporal dynamics of the exciton photoluminescence (PL) in ZnO nanorod samples was investigated experimentally as a function of temperature and excitation intensity. Excitonic photoluminescence is observed up to room temperature. The excitation dependence of the PL dynamics reveals a saturable non‐radiative recombination center. Under high excitation conditions the time‐resolved photoluminescence shows two components: the ZnO M‐band which decays with a temperature independent sub‐100 ps time constant, and the intrinsic exciton PL with a time constant of several 100 ps increasing with temperature. Exciton‐exciton scattering effects are notably absent, which is attributed to the reduced polariton phase space resulting from the small nanorod diameter of 50 nm.