Lasing and optical properties of ZnMgSSe/ZnSe-, ZnMgSSe/ZnSSe/ZnSe-, and ZnMgSSe/ ZnMgSSe/ZnSe-based single-and multiple-quantum-well heterostructures grown by metalorganic vapor phase epitaxy were studied, and the characteristics were found to depend on the excitation intensity I exc , temperature, and well width. Laser action under transverse optical pumping was achieved only for well widths L z у4 nm and optical confinement factors ⌫Ͼ0.04. In separate confinement heterostructures, lasing

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... the lowest threshold (I thr ϭ10-30 kW/cm 2 at Tϭ78 K) was achieved and device characteristics were studied up to Tϭ577 K. © 1998 American Institute of Physics. ͓S0003-6951͑98͒04237-5͔ Zinc selenide remains one of the most important semiconductors for blue-green lasers, despite the recent breakthrough in III-V GaN-based devices. 1 The latter does not cover the blue-green region at present. Quantum-well ͑QW͒ II-VI-based heterostructures are promising for vertical cavity lasers, optical switches, and modulators. Metalorganic vapor phase epitaxy ͑MOVPE͒ is the most suitable method for the mass production of such devices. After the report of the first II-VI-based junction laser in 1991, 2 a great number of investigations have been devoted to the understanding of ptype doping of ZnSe, and to the understanding of the lasing properties of ZnSe epitaxial layers and ZnSe-based heterostructures using external electron-beam or optical excitation. 3-11 Room-temperature optically pumped lasing of ZnSe-based QW heterostructures grown by MOVPE has been achieved by several groups, 3,4,6,7 using ZnSe/ZnSSe multiple-quantum-well ͑MQW͒ heterostructures 3,4,6 or ZnSe/ ZnMgSSe double heterostructures. 7 The main aim of our work was the investigation of the influence of the type of heterostructure, well width L z , and optical confinement factor ⌫ on the laser threshold and on the possibility of achieving high-temperature lasing. The heterostructures were grown on GaAs substrates in a low-pressure MOVPE reactor at a total pressure of 400 hPa and a growth temperature of 330°C, using dimethylzinc triethylamine adduct ͓DMZn͑TEN͔͒, ditertiarybutylselenium ͑DTBSe͒, ditertiarybutylsulphur ͑DTBS͒, and bismethylcyclopentadienylmagnesium ͓͑MeCp͒ 2 Mg͔ as precursors. This combination allows the reproducible adjustment of the sulphur and magnesium content in a wide range ͑currently, up to 49% S and 59% Mg͒, maintaining high-crystal homogeneity and almost lattice-matched growth. The following types of heterostructures with different L z were prepared and studied: double heterostructures with single QW and MQW ͑DH-SQW, DH-MQW͒ with ZnMgSSe (E g ϭ3.01 eV) barrier layers, separate confinement MQW heterostructures ͑SCH-MQW͒ with ZnSSe (E g ϭ2.87 eV) guiding layers and ZnMgSSe (E g ϭ3.05 eV) cladding layers, and SCH-SQW with ZnMgSSe (E g ϭ3.01 eV) guiding layers and ZnMgSSe (E g ϭ3.32 eV) cladding layers. The surfaces of all structures were covered with a thin ZnSe cap layer to avoid oxidation. Nitrogen laser radiation with a power of Pϭ20 kW, a wavelength of ϭ337.1 nm, a pulse duration of t exc ϭ10 ns, a repetition rate of f ϭ1000 Hz, and an excitation intensity I exc from 0.1 W/cm 2 up to 1.5 MW/cm 2 was used for pumping and for photoluminescence ͑PL͒ measurements over the temperature range Tϭ78-577 K. Laser cavities with a length between 0.2 and 1 mm were fabricated by cleaving the heterostructures and substrates, previously thinned down to 50-100 m. The PL and lasing spectra were recorded using a monochromator, a photomultiplier, and a stroboscopic DA converter, with a spectral resolution about 0.05 nm. At Tϭ78 K, the PL spectra from the surface of a ZnMgSSe/ZnSSe/ZnSe SCH-MQW heterostructure (L z ϭ4 nm) appear to be of excitonic nature at lower excitation levels. One can see in Fig. 1͑a͒ that the excitonic band does not shift as I exc increases, but a new radiation band at 441.6 nm ͑marked by an arrow͒ becomes visible. The band is separated by 5 meV from the excitonic one, becomes dominant at I exc Ͼ30 kW/cm 2 ͑near laser threshold͒ and does not shift with I exc up to 500 kW/cm 2 , when the stimulated emission from the sample surface emerges. For comparison, the shift of the electron-hole plasma ͑EHP͒ band in homogeneous ZnSe epilayers with a ZnMgSSe barrier layer between ZnSe and GaAs in the same range of I exc is about 13 meV, and in ZnSe:N layers the shift is approximately 20 meV. 11 We believe that the new emission band at high excitation intensity originates from recombination in an electron-hole plasma produced by a high nonequilibrium carrier concentration, which is most probably responsible for the gain mechanism in our structures. All SQW and MQW structures with L z у4 nm showed a a͒ Present address: