E. Lach

Optical properties of wire and dot structures for photonic applications

Abstract The realization and physical investigation of wire and dot structures will be reported. Fabrication requirements for low dimensional semiconductor structures will be discussed for masked implantation enhanced intermixing technique (MIEI) and for dry etching technique with subsequent overgrowth. With dry etching technique wire structures down to 30 nm could be achieved. With MIEI technique wire structures down to 40 nm and dot structures down to a radius of 100 nm could be achieved. A quantum efficiency of 0.84 can be obtained for etched and overgrown wires at 65 nm and an increase of the quantum efficiency of more than 3 orders of magnitude compared to as etched wires could be demonstrated. Strong size dependent carrier capture and carrier relaxation effects can be demonstrated in wires. The observed carrier relaxation in 1D semiconductors is strongly reduced if wires become smaller. Band filling effects and band gap renormalization of the 1D electron-hole plasma (1D EHP) could be determined over a wide range of wire widths. Appreciable size effect of the 1D EHP can be demonstrated for both etched and implanted wires. The experimental band gap renormalization of the 1D EHP appears weaker than for 2D EHP as expected and is stronger than the theoretical 1D band gap renormalization for an ideal 1D EHP due to its quasi 1D dimensionality.

Investigation of the 2D–3D transition of the band gap renormalization in GaAs

We have analyzed the band gap renormalization due to many body effects in electron-hole plasmas in GaAs in the transition region between two-dimensional quantum wells and bulk material. The band gap renormalization depends strongly on the well widths. A transition of the band gap renormalization from the two-dimensional behavior observed for quantum wells with widths Lz<8 nm to the behavior of bulk GaAs occurs for well widths between 10 and 20 nm.

Bandgap renormalization at finite carrier densities in semiconductor quantum wells and mesa structures

Abstract Theoretical and experimental results for the band gap renormalizations in lattice matched In 53 Ga 47 As/InP quantum wells are given and compared. The theoretical results involve fully self-consistent calculations of the subband energies using a generalization] of the local density approximation for two component electron-hole systems. The experimental results are obtained from photoluminescence studies at high excitation of quantum wells in mesa structures. The band gap renormalization is found to depend on the indices of the subbands involved, which results from the symmetries of the subband wavefunctions.

Optical investigation of 2D Mott transitions in GaAs/GaAlAs quantum well structures

Abstract In transmission experiments performed under quasi-equilibrium conditions at low temperatures we investigated the bleaching of the quasi-2D excitons in GaAs/GaAlAs MQW structures with special emphasis on the behaviour of the excitons at the different subband edges. The 1hh excitons are found to be much more sensitive to bleaching than the other excitons. We attribute this to phase space filling effects which should reduce the 1hh excitonic structures additionally to the usual screening due to the long-range Coulomb interaction, which screens the excitons related to transitions between higher subbands only. We determined the 2D Mott density of the 2hh exciton performing a lineshape analysis of the luminescence of the electron-hole pairs measured simultaneously.

Many Body Effects in Homogeneous Quasi 2D Electron-Hole Plasma in Undoped and Modulation Doped INGaAs Single Quantum Wells

During the past few years a number of studies have addressed the properties of an electron-hole plasma (EHP) in three-dimensional (3D) and two-dimensional (2D) semiconductor structures. The many body effects in the dense quasi-2D electron-hole (e-h) system were discussed in(1–6). Interparticle interactions in a dense e-h system in a semiconductor lead to a renormalization both of the band gap and of the electron and hole dispersion laws. In many-particle theory, these changes are described by a self-energy Σ, which depends on the energy e and quasi momentum k of the quasi particles(7,8). ReΣ describes the renormalization of the dispersion laws for noninteracting electrons and holes.

Spectroscopic investigation of electron-hole plasma properties in InGaAs/InP quantum well structures

Abstract Using photoluminescence we investigated the properties of quasi-two-dimensional electron-hole plasmas in lattice-matched InGaAs/InP-multi-quantum well structures under quasi-stationary excitation. From the lineshape analysis of the spectra we obtained the plasma parameters and information on the subband structure. From optical transitions between higher subbands we determine the conduction band discontinuity to be 210meV, corresponding to 35% of the total discontinuity.