Y. Jen

Stimulated Emission Processes in Zn1-xCdxSe/ZnSe Multiquantum Wells

A stimulated emission effect has been studied in Zn1-xCdxSe/ZnSe (x=0.3) multiquantum wells (MQWs) with the well width of 7 to 70 A. The luminescence spectrum of the quantum well (QW) exciton at 4.2 K is shifted from the absorption spectrum by 10-12 meV to the lower-energy side. The deviation of the peak energy of the luminescence shows that the excitons in the MQW are inhomogeneously broadened by the monolayer fluctuation of the QW width. Stimulated emission is observed in the low-energy shoulder of the exciton luminescence band, which shifts to lower energies with increasing excitation intensity. The gain process is explained by the exciton-exciton scattering in the MQWs.

High-field magnetization of Sn1−xEuxTe:EuTe

Abstract The magnetization M of Sn 1− x Eu x Te:EuTe, x ≦0.02, has been measured at 4.2 K in fields H up to 23 T. The average pair exchange interaction is antiferromagnetic with a value of about 0.5 K. For x -values greater than 0.014 the M vs. H curves show a definite knee with approximately linear behavior above and below the knee. The knee in the magnetization data and a cusp in the susceptibility at about 10 K are related to the presence of EuTe clusters in our samples.

Stimulated blue emission processes in Zn1−xCdxSeZnSe multi-quantum wells

Abstract Stimulated emissions in Zn 1−x Cd x Se ZnSe multi-quantum well (MQW) structures have been studied under high optical excitation in the temperature range 4.2–300 K. With increasing the excitation intensity, the stimulated emission at low temperatures shows a red shift of the peak energy and a quadratic dependence of the intensity on the excitation intensity. The observed stimulated emission process is interpreted by exciton-exciton scattering in the MQWs. At room temperature, highly excited MQWs show a markedly broadened emission, the intensity of which is in proportion to the excitation intensity. We attribute the emission process to electron-hole plasma (EHP) recombination. The observed emission spectra are in good agreement with calculations by using models of exciton-exciton scattering and EHP recombination. The stimulated emission mechanisms elucidated in the present study are closely related to those taking place in ZnSe-based blue laser diodes.

Magnetization studies of Sn1−xEuxTe

Abstract The magnetization M of Bridgman-grown Sn1−xEuxTe has been measured at 4.2K in fields H up to 23T. For x

Photoluminescence and Raman studies of Zn0.7Cd0.3Se/ZnSe short period strained-layer superlattices grown by hot wall epitaxy

Optical and structural studies on short period Zn0.7Cd0.3Se/ZnSe strained-layer superlattices (SLS) grown by hot wall epitaxy have been performed experimentally using photoluminescence and Raman scattering. We have found an additional luminescence peak (in our shorter period SLS) at higher energy than the dominant exciton transition peak. From our Raman scattering measurements and a Kromg-Penney model for calculating excitonic transitions in quantum wells, this phenomenon can be interpreted in terms of monolayer-type interface fluctuation.

Spontaneous and Stimulated Emissions of Confined Excitons in Zn1-xCdxSe Multi-Quantum Wells

Photoluminescence in Zn1-xCdxSe/ZnSe multi-quantum wells (MOWs) have been studied under various excitation intensities and compared with the absorption spectrum. A stimulated emission by the quantum well (QW) excitons appears shifted by 8 meV from the peak of the spontaneous emission band at an excitation power density of 0.25 MW/cm2. Above 1 MW/cm2 the emission spectrum broadens and shifts further to the lower energy side. The observed stimulated emissions are interpreted by the recombination due to the exciton-exciton scattering and by the electron hole plasma recombination in the MQWs.

Photoluminescence of heavily doped GaAs/AlGaAs quantum wells in high magnetic fields

Abstract We studied the photoluminescence in GaAs/AlGaAs single quantum wells at fields up to a maximum of 22 T and observed spectra due to impurities, heavy-hole excitons, and Landau levels. The wells were doped with Si at different doping levels up to 3 × 10 18 cm −3 in order to examine this influence on the photoluminescence. We compare results from two well widths, 50 A and 100 A, over an energy range from about 1.4 to 1.7 eV. From the dependence on field of the Landau levels, a cyclotron mass ratio of 0.11 ± 0.02 was determined, which is larger than the bulk GaAs mass ratio of 0.067. The heavy-hole exciton binding energy was about 15 meV for the 100 A well.