Effect of Coulomb enhancement on optical gain in (Zn,Cd)Se/ZnSe multiple quantum wells (original) (raw)
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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.
Optical gain in (Zn,Cd)SeZn(S,Se) quantum wells as a function of temperature
Journal of Crystal Growth, 1998
We have investigated the mechanism of stimulated emission in ZnCdSe-ZnSSe quantum wells through measurements of the optical gain spectrum between 77 and 270 K. We also calculated the optical gain using a model which included many-body effects and found excellent agreement with our measurements. Our results are inconsistent with an excitonic gain mechanism and we conclude that the stimulated emission arises from an electron-hole plasma in our samples. However, we find that the electron-hole Coulomb interaction is still significant at room temperature in II-VI heterostructures.
Optical gain in ZnCdSe-ZnSe quantum well structures
Physics and Simulation of Optoelectronic Devices IV, 1996
ABSTRACT We have measured the gain spectrum of an optically pumped 40 angstrom ZnCdSe-ZnSe multiple quantum well. Our calculation, which includes many body effects such as Coulomb enhancement and spectral broadening due to carrier scattering, gives excellent agreement with the experimental gain measurements. We then show the importance of the inclusion of the Coulomb enhancement for the calculation of optical gain when predicting laser threshold currents. This is emphasized by using our gain calculation as a basis to theoretically optimize a simple ZnCdSe-ZnSe quantum well laser structure incorporating the leakage current over the p-type cladding.
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.
1996
The exciton stability in Zni_,Cd,Se/ZnSe multiple quantum wells has been investigated by absorption and magneto-luminescence spectroscopies in undoped and modulation-doped samples. The well width and the composition dependence of the exciton binding energy has been determined experimentally and compared with the value obtained with theoretical calculations. The absorption saturation has been investigated in modulation-doped samples as a function of the sheet carrier density. The exciton stability has been correlated to the actual lasing mechanism in samples with different structure and composition. Freecarrier recombination dominates the stimulated emission of Zni_,Cd,Se quantum wells with relatively low exciton binding energy, whereas a dominant excitonic character is found in the lasing of deep and narrow quantum wells. Stimulated emission experiments in high magnetic fields performed on various samples confirm this attribution.
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
Radiative recombination processes in ZnSe/ZnSexSe1−x multiple-quantum-well structures
Wide-Band-Gap Semiconductors, 1993
Radiative recombination processes in highly excited ZnSeiZnS,, IXSe, L(2 multiple-quantum-well structures have been investigated as a function of the well width and of the lattice strain. Excitonic scattering processes dominate the photoluminescence spectra. An optical amplification process is observed, up to room temperature, due to inelastic exciton-exciton scattering. An optical excitation threshold around 300 kW/cm' at 300 K and 8.4 kW/cm' at 10 K was measured for the stimulated emission.
Thermal and electrostatic stability of biexcitons in Zn1−xCdxSe/ZnSe quantum wells
Journal of Crystal Growth, 1998
We investigated the density and temperature dependence of biexciton recombination in Znl _,Cd,Se/ZnSe quantum wells grown by molecular beam epitaxy. Modulation-doped structures allowed us to investigate the electrostatic stability of biexcitons in the presence of a precise concentration of free carriers. Doping was introduced in the central part of the barrier up to a doping concentration of 3.4 x 10" cm3. The comparison between the two sets of samples allowed us to clarify the role of each elementary excitation as far as lasing is concerned. Although the biexciton binding energy in our undoped samples was sufficiently higher than in 111-V materials, biexcitons are not stable at temperatures greater than 50 K. Moreover, the electrostatic screening and many-body effects caused by free-carriers decrease the biexciton binding energy so that biexcitons are not observed in modulation-doped samples. We found that the vicinity of the stimulated emission line at threshold with the peak of biexcitonic recombination, is not a sufficient criterion to conclude that lasing is biexcitonic in origin. cs
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