Strain Effects in Superlattices of Diluted Magnetic Semiconductor ZnTe/Zn1-xMnxTe

ABSTRACTZnTe/Zn1-xMnxTe superlattices were grown on GaAs (001) substrates by molecular beam epitaxy. The multi-phonon processes including overtones and combinations of optical phonons have been studied by near resonant Raman scattering in the temperature range 13 K to 300 K. The strain arising from lattice mismatch gives rise to a shift in the optical-phonon frequencies. A two-phonon interface mode of superlattice has been observed and identified for the first time. Strain-induced red shifts of exciton energies related to transitions from the conduction subband to the light-hole and heavy-hole subband have been found by photoreflectance measurements. Experimental results agree well with the calculated strain-induced shift in superlattices.

Photoluminescence Studies of [(CdSe)1(ZnSe)2]9-ZnSeTe Multiple Quantum Wells Under High Pressure

ABSTRACTWe have performed photoluminescence (PL) measurements at liquid nitrogen temperature under high pressure up to 5.5 GPa and in the temperature range 10-300 K at atmospheric pressure on {(ZnSe)30(ZnSe0.92Te0.08)30(ZnSe)30[(CdSe)1(ZnSe)2]9}x5 multiple quantum wells. The PL peaks, EB, E1 and Ew corresponding to the band edge luminescence in ZnSe barrier layer, the transitions from the first conduction subband to the heavy-hole subband in ZnSe0.92Te0.08 layers and [(CdSe)1(ZnSe)2]9 ultra short period superlattice quantum well (SPSLQW) layers have been observed. Experimental results show that ZnSe0.92Te0.08/ZnSe forms a type-I superlattice (SL) in contrast to the type-II ZnSe/ZnTe SL. The pressure coefficients of the EB, E1 and Ew exciton peaks have been determined as 67, 63 and 56 meV/GPa, respectively. With increasing temperature (or pressure), the E1 peak-intensity drastically decreases which is attributed to the thermal effect (or the appearance of many defects in ZnSe0.92Te0.08 under higher pressure).

Characterization of Undoped Pseudomorphic InGaAs/GaAs Quantum Wells by Electron Beam Electroreflectance (EBER) and Photoluminescence (PL)

We have investigated the interband optical transitions within undoped pseudomorphic InyGa1-yAs/GaAs quantum wells of a range of thickness from 50Å to 150Å, and y values 0.1 to 0.2. From photoluminescence (PL), we identify the lowest interband transitions. Electron beam electroreflectance (EBER) modulation spectroscopy is utilized to detect the lowest and the higher energy interband transitions within the quantum wells. We compare the measured interband energies to those calculated theoretically.We have observed exciton-like transitions attributable to the heavy hole and light hole levels and most importantly, confined states of the split-off valence band, not reported to date. The multiplicity of observed quantum transitions allows rectangular barrier model parametrization of these wells, using hypothetical strain splitting of the various subbands. For five such quantum wells, we find the estimated indium contents and well widths to be nearly nominal, with consistent values between independent 300K and 100K data. With respect to the heavy hole subband, the conduction band offset Qc is estimated to be 0.586 ±0.024. With suitable values, all of the transitions, including those of the splitoff band, are predicted accurately.