II-VI Semiconductor Heterostructures Research Articles

Gain spectroscopy of excitonic molecules and its dynamics in a ZnSe single quantum well.

We demonstrate spectroscopically how optical gain is formed in an interacting system of excitons and biexcitons in a single ZnSe quantum well. The dynamics of gain formation are studied on a subpicosecond time scale in pump-probe experiments, revealing the influence of coherent effects and the impact of exciton-exciton and exciton-biexciton interactions. Spectrally resolved, polarization-dependent degenerate four-wave-mixing experiments further demonstrate how the excitonic many-body phenomena profoundly influence the nonlinear optical response in this II-VI semiconductor heterostructure. \textcopyright{} 1996 The American Physical Society.

Computer simulation study on the atomistic and electronic structures of semiconductor heterostructures

The atomic and electronic structures of semiconductor heterostructures are investigated by using the tight-binding (TB) electronic theory, taking into account the realistic atomic irregularities, such as steps and misfit dislocations at the interface. Particular attention has been paid to the 1/2〈110〉(001) misfit dislocation of the wide gap II-VI semiconductor heterostructures, like ZnSe/GaAs(001) systems. It is shown that steps at the interface do not produce deep gap states, but they influence significantly the deep states associated with the misfit dislocations. The stability and degradation of II-VI semiconductor heterostructures are discussed in terms of the introduction of the misfit dislocations.

Observation of the quantum confined stark effect in ZnSe/ZnCdSe single quantum well systems

We report the observation of the quantum-confined Stark effect (QCSE) in ZnSe/ ZnCdSe single quantum wells grown by molecular beam epitaxy, using photoluminescence. In our experiments the electric field was applied via a reverse-biased Schottky barrier contact. To our knowledge, this is the first observation of the QCSE in any wide gap II-VI semiconductor heterostructure. Significant red shifts, typically 10–15 meV, are detected before quenching. An associated reduction in the transition intensity, consistent with the QCSE. is clearly observed. The dependence of these results will be discussed as a function of quantum well depth and thickness. Complete quenching of the luminescence is observed with applied voltages as low as 5 V. In addition, at lowest voltages, we also detect small blue shifts (up to 4 meV), which we attribute to the interaction between the externally applied electric field and the built-in field of the structure.

(Zn,Cd)Se/ZnSe quantum-well lasers: Excitonic gain in an inhomogeneously broadened quasi-two-dimensional system.

Optical properties of a strongly excitonic quasi-two-dimensional system in a wide-band-gap II-VI semiconductor heterostructure are investigated in terms of the relationship between absorption and stimulated emission. In particular, the optical gain in (Zn,Cd)Se/ZnSe quantum-well lasers is demonstrated to be of excitonic nature over a wide range of temperatures, and to occur at electron-hole pair densities below the exciton-electron hole plasma transition. Both steady-state and transient (picosecond and femtosecond) spectroscopic techniques have been applied to detail exciton kinetics within the n=1 heavy-hole exciton resonance. A phenomenological model of optical gain is proposed, originating from an inhomogeneously broadened exciton resonance and including the effects of exciton-phonon interaction.

Blue laser diodes and LEDs based on II-VI semiconductor heterostructures

The authors report the first observation of blue stimulated emission from a semiconductor laser structure. At 77 K, under pulsed current injection, the laser devices output light in the blue spectral region at wavelengths as short as 475.4 nm (2.606 eV). The laser structure consists of a single separate-confinement approximately 200-AA quantum well of Zn/sub 0.85/Cd/sub 0.17/Se centered in a ZnSe light-guiding layer (1- mu m thick). Top ( approximately 1.0 mu m) and bottom ( approximately 1.5 mu m) cladding layers of ZnS/sub 0.1/Se/sub 0.9/, along with the ZnSe light-guiding layers, were doped p-type and n-type, respectively. All of the major constituents of the various layers of the heterostructure were grown by MBE (molecular beam epitaxy) using elemental Zn, Cd, Se, and S. LEDs (light emitting diodes) have also been fabricated which emit bright blue light (dominant wavelength as short as 479 nm) at room temperature. The p-on-n heterostructure LEDs exhibit excellent electrical properties as well: mesa devices (area=3*10/sup -3/ cm/sup 2/) produce 25 mA at 4.4 V at 300 K. Green and blue/green LEDs have also been fabricated and studied.

The Mbe Growth of Widegap II-VI Injection Lasers and LEDs

ABSTRACTStriking progress in the development of II-VI semiconductor heterostructures, coupled with seminal advances in doping, has very recently led to the first demonstration of blue and blue/green diode lasers operating from cryogenic to room temperature. The active region in these devices was based on the (Zn, Cd)Se/ZnSe multiple quantum wells (MQW) which had earlier been actively studied as a candidate for laser medium by optical pumping techniques. We report on the performance of such MQW diode lasers with emphasis on structural versatility in terms of preparation on both p-type and n-type GaAs substrates, and where sulfur is or is not incorporated for blue/green color lasing. In this work we have obtained pulsed, high power, high quantum efficiency laser emission up to near room temperature conditions. Efficient LED devices are described which operate in the blue (494nm) at room temperature.

Blue Lasers Based on II-VI Semiconductor Heterostructures

ABSTRACTProperties of blue laser diodes based on ZnSe-related II-VI semiconductor heterostructures are reported. At 77 K, continuous-wave (cw) operation has been achieved for lasers emitting at wavelengths as short as 470.4 nm (2.635 eV), while pulsed laser emission has been observed up to ∼200 K, for samples with uncoated facets. Measured turn-on voltages for stimulated emission at 77 K were as low as 12 V for some of the laser diodes due to improved ohmic contacts. For some particular devices, differential quantum efficiencies as high as 36% per (uncoated) facet have been obtained at 77 K.