V. I. Kozlovsky

Vapour growth and characterization of bulk ZnSe single crystals

Large (up to 60 mm in diameter) untwinned ZnSe single crystals have been grown in sealed quartz ampoules by seeded physical vapour transport and seeded chemical vapour transport with hydrogen. The dependence of structure perfection on the seed quality and its orientation, the source design, the gas filling of the growth ampoule and the temperature regime was researched. Selective chemical etching topography, X-ray diffraction rocking curve and cathodoluminescence studies are presented to characterize grown crystals. The influence of oxygen impurity on crystal emission and weakening of this influence in crystals grown in hydrogen was found. The results of crystal annealing in Zn vapour and Zn melt are discussed.

Vapour growth of II-VI solid solution single crystals

Abstract A modified vapour phase free growth method for obtaining homogeneous single crystals of solid solutions of II–VI compounds having essentially different saturated vapour pressures is described. Single crystals of ZnCdSe, ZnCdS, ZnCdSSe, ZnSTe, ZnSeTe, CdSTe of 40–55 mm in diameter have been grown by this technology. Thermodynamic analysis of the growth process of the ZnSeCdSe system has been carried out and its results are in a good agreement with experiment.

Study of a 2-J pulsed Fe:ZnSe 4-μm laser

We report the results of a study of a pulsed Fe:ZnSe laser for temperatures ranging from 85 to 295 K. With a free-running Er:YAG laser, operating at 2.94 μm, as a pump source, a maximum output energy of 2.1 J at 85 K was produced at a wavelength of 4.1 μm. The optical-to-optical efficiency of the laser was 35% at maximum energy while the maximum absorbed energy slope efficiency was as high as 51%. By operating at 245 K (a temperature which can be easily reached using thermoelectric coolers) we achieved 1.3 J of output energy from an Fe:ZnSe laser, with a slope efficiency of 29% (23% optical-to-optical efficiency). The maximum output energy reached 42 mJ at room temperature (295 K). The temperature dependence of the lifetime of the 5T2 energy level of Fe2+ in ZnSe was studied in the 275–365 K temperature range. The activation energy for nonradiative relaxation was found to be 2235 cm−1.

Investigation of e–h pair compression in molecular beam epitaxy grown ZnCdSe/ZnSe multiquantum wells at volume excitation by electron beam

Comparative cathodoluminescence (CL) study of the molecular-beam epitaxy grown ZnCdSe/ZnSe multiquantum well (MQW) structures differing by the number of QWs (4, 15, 30, 100) has been carried out. The total thickness of MQW part for all structures equals 1.5 μm. The CL intensity of the four QW structure has been found to be the highest, which provides evidence on the high efficiency of the carrier collection into QWs even in the case when the ZnSe barrier thickness is as large as 0.5 μm. Cleaved edge cavities for transverse e-beam pumping have been cleaved from these structures but a lasing action has been achieved on the four QW structures only because of the highest carrier compression in this structure. Based on the independence of the carrier collection efficiency on the barrier thickness, the estimation of the optimal number of QWs in the e-beam pumped MQW vertical cavity surface emitting lasers has been carried out. The MQW structure with only five QWs should be used for the cavity losses to be as sm...

Electron-beam pumped laser structures based on MBE grown ZnCdSeZnSe superlattices

Cathodoluminescence (CL), photoreflection (PR), phototransmission (PT) of single and multiquantum wells (MQWs) and strain layer ZnCdSeZnSe superlattices (SLs) grown by molecular beam epitaxy (MBE) were studied. An increase of the Stokes shift with the number of quantum wells (QWs) and the appearance of new lines in CL and PT spectra were observed. Room temperature (RT) vertical-cavity surface-emitting laser (VCSEL) operation was achieved by using the SL structures. Output power up to 2.2 W in single longitudinal mode with λ = 493 nm was obtained. Cut facet laser wavelength of the same SL structure was 502 nm.

3 J pulsed Fe:ZnS laser tunable from 3.44 to 4.19 μm

We report the laser properties of Fe:ZnS in the temperature range from 85 to 186 K. Under pumping by a pulsed free-running 2.94 μm Er:YAG laser, a maximum output energy of 3.25 J at 85 K was produced with 27% optical-to-optical efficiency. The output wavelength was observed to tune with temperatures from 3.60 μm at 85 K to 3.78 μm at 186 K. As the temperature was increased, the absorbed energy slope efficiency decreased from 42.4% at 85 K down to 2.5% at 183 K. With a CaF2 prism, the Fe:ZnS laser could be tuned from 3.44 to 4.19 μm at 85 K.

E-Beam Longitudinally Pumped Laser Based on ZnCdSe/ZnSe MQW Structure Grown by MBE on ZnSe(001) Substrate

Electron beam longitudinally pumped laser based on 15 ZnCdSe/ZnSe QW periodic-gain structure grown by molecular beam epitaxy on ZnSe(001) substrate was studied. An output power of 0.3 W was achieved. The laser wavelength was in 518-536 nm range, being at the short wavelength side of the QW emission line at low excitation level. Such unusual feature was explained by the participation of excited QW levels in the creation of the optical gain.

High-Output-Power Ultraviolet Light Source from Quasi-2D GaN Quantum Structure.

Quasi-2D GaN layers inserted in an AlGaN matrix are proposed as a novel active region to develop a high-output-power UV light source. Such a structure is successfully achieved by precise control in molecular beam epitaxy and shows an amazing output power of ≈160 mW at 285 nm with a pulsed electron-beam excitation. This device is promising and competitive in non-line-of-sight communications or the sterilization field.

2.92 µm Cr2+:CdSe single crystal laser pumped by a repetitively pulsed Tm3+:Lu2O3 ceramics laser at 2.066 µm

A laser oscillator based on Cr2+:CdSe single crystal pumped by 2.066 µm radiation of a Tm3+:Lu2O3 ceramic laser was created and investigated. Repetitively pulsed oscillations at a wavelength of 2.92 µm with a bandwidth of 80 nm were demonstrated. The output power was up to 350 mW at 10 kHz repetition rate with a pulse duration of ~200 ns in the good-quality beam.

Electron Beam Pumped MQW InGaN/GaN Laser

E-beam pumped lasers are attractive for Laser Cathode Ray Tubes (LCRT) in projection displays and a variety of applications typically associated with optically pumped lasers. For the first time an InGaN/GaN multiple quantum well (MQW) in-plane laser pumped by surface normal pulse and scanning electron beams was demonstrated. Pumping at room temperature (RT) and 80 K showed peak stimulated emission wavelengths of 402 and 409 nm with a full width half maximum (FWHM) of 0.6 nm and 1.2 nm, respectively. The threshold electron beam current densities have been estimated as 60 A/cm 2 for 35 keV electron energy at 80 K using scanning e-beam pumping and 200-300 A/cm 2 at RT using pulsed e-beam pumping with a maximum electron energy of 150 keV. At 80 K, light output of 150 mW was measured out of one facet at an e-beam current of 1.7 mA.