Optical gain in (Zn,Cd)SeZn(S,Se) quantum wells as a function of temperature (original) (raw)

Optical gain in (Zn, Cd)Se–Zn(S, Se) quantum wells

Journal of the Optical Society of America B, 1998

We have investigated the mechanism of stimulated emission in ZnCdSe-ZnSSe quantum wells through optically pumped measurements of the gain spectrum in a variety of structures from 270 to 77 K. We also calculated the optical gain, using a model that includes many-body effects, and found excellent agreement between the calculated gain line shapes and our measurements. Under the conditions studied, which are close to those found in an operating laser diode, we conclude that the stimulated emission arises from an electronhole plasma in our samples, even down to 77 K. Although our measurements do not rule out exciton gain mechanisms at other temperatures or operating conditions, sensitive line-shape fitting does not require them in our case. However, our line-shape analysis does show that Coulomb enhancement is significant, even at room temperature.

Effect of Coulomb enhancement on optical gain in (Zn,Cd)Se/ZnSe multiple quantum wells

Physical Review B, 1996

The optical-gain spectra of a 40-Å ͑Zn,Cd͒Se/ZnSe multiple quantum well has been measured at various temperatures using a variable-stripe method. By comparison with a gain calculation including many-body effects, we have shown that gain in this structure arises from an electron-hole plasma ͑EHP͒ for temperatures higher than 140 K. Excellent agreement between experiment and theory allows us to demonstrate the significance of many-body effects such as carrier dephasing and Coulomb enhancement. The breakdown of the EHP model below 140 K indicates an increasing excitonic contribution.

Excitonic Gain and Laser Emission in ZnSe-Based Quantum Wells

Physical Review Letters, 1992

We show spectroscopically that the origin of optical gain and laser emission in (Zn, Cd)Se/ZnSe quantum wells at blue-green wavelengths is of excitonic nature. This circumstance derives from the large enhancement in the exciton binding and its oscillator strength which occurs in the quasi-2D case, so that an exciton gas is stable against ionization by optical phonons up to room temperature and that gain in the context of partial phase-space filling can develop at pair densities below the onset to an electron-hole plasma.

Stimulated emission and optical gain in a single MOVPE-grownZnxCd1−xSe−ZnSequantum well

Physical Review B

We have studied the stimulated emission from an optically pumped graded index separate confinement heterostructure, realized in the form of a metal-organic vapor-phase-epitaxy-grown single quantum well based on a wide-gap ͑ZnCd͒Se semiconductor. The structure is composed of a central Zn 0.78 Cd 0.22 Se quantum well sandwiched between two thicker, zinc-rich ͑ZnCd͒Se layers with a graded cadmium composition varying continuously and monotonously between 0% and 5%. The stimulated emission occurred at ϳ2.49 eV (T ϭ8.5 K), being spectrally redshifted with increasing temperature and disappearing for Tу200 K. The optical gain has been measured using the variable stripe-length method, and values of the gain up to 620 cm Ϫ1 have been achieved. High-resolution spectral studies of the stimulated emission have revealed a fine structure in the emission spectra originating from different localization sites for excitons. We identify the lasing mechanism as due to an inhomogeneously broadened system of localized excitons. ͓S0163-1829͑98͒04320-3͔

Excitonic and Raman properties of ZnSe/Zn1−xCdxSe strained-layer quantum wells

Journal of Applied Physics, 1991

The optical properties of strained-layer ZnSe/Zn0.86Cd0.14Se single quantum wells have been studied. The photoluminescence under direct and indirect excitation is investigated in detail. The temperature dependence of photoluminescence and resonant Raman scattering are investigated. Very strong 2LO-phonon Raman scattering has been observed with Zn0.86Cd0.14Se quantum wells, where the scattered photon energy is in resonance with an exciton transition. Experimental exciton energies are compared with a finite-square-potential quantum-well model including band nonparabolicity and the strain effect. Based on Hill’s theory [J. Phys. C 7, 521 (1974)] we have computed the band gap of Zn1−xCdxSe as a function of composition x.

Thermal effect on quantum confinement in ZnS0.06Se0.94/Zn0.8Cd0.2Se quantum wells

Solid State Communications, 2001

ZnS 0.06 Se 0.94 /Zn 0.8 Cd 0.2 Se quantum wells (QW) were studied by temperature-dependent photoluminescence (PL) measurement. We observed two PL peaks due to the band-to-band transition in ZnS 0.06 Se 0.94 barrier, E g 0 2:819 eV; and the transition of heavy hole to ®rst conduction subband in Zn 0.8 Cd 0.2 Se well, E hh1 0 2:545 eV: The relative thermal coef®cients of these two constituent materials are quite different, resulting in a temperature-dependent quantum con®nement. The reduction of the quantum con®nement at high temperatures induces a leakage of carrier and leads to a quenching of the PL intensity. The activation energy for the PL quench is about 188.4 meV. q

Charged excitons in ZnSe-based quantum wells

Physical Review B, 1999

We report on magneto-optical studies of ZnSe/͑Zn,Mg͒͑S,Se͒ quantum wells with n-type and p-type modulation doping. Negatively and positively charged excitons related to the heavy-hole exciton states are found and identified by their polarization properties. Negatively charged excitons formed with light-hole exciton states are observed. Their binding energy is about 20% less than that related to the heavy-hole exciton. The exciton and trion parameters ͑radiative and nonradiative dampings͒ are determined. ͓S0163-1829͑99͒50136-7͔

Effect of structural imperfections on luminescence of ZnCdSe/ZnSe quantum wells

Journal of Alloys and Compounds, 2004

The structural and luminescence properties of Zn 1−x Cd x Se/ZnSe multi-quantum well (MQW) structures with high molar fraction of cadmium (30-50%) and wide ZnSe barriers (50, 100 and 500 nm) grown by molecular beam epitaxy (MBE) have been investigated by high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) methods. It is shown that the fluctuations of composition within the quantum well layer determine the full-width at half maximum (FWHM) of the QW photoluminescence peak. The unusual polarization characteristics of this photoluminescence have been observed. The emission peak in the edge geometry is strongly polarized perpendicularly to the QW plane. This effect is ascribed to the localization of the ground-state heavy-hole-like excitons in the regions with increased cadmium content.