MOVPE growth and study of ZnCdSe/ZnSSe MQW structures for green VCSELs

Abstract

ZnCdSe/ZnSSe MQW structures for an electron beam pumped VCSEL with resonant periodic gain were grown by MOVPE at 425-470 °C. Strong contamination of the structure by Ga from a GaAs substrate was found and its effect on the growth rate and photoluminescence characteristics was studied. A protective thin ZnSSe layer deposited at lower temperature (350 °C) or thin layers of ZnS and ZnS/ZnSSe SL grown at temperature 425-470 °C prevent Ga penetration and allowed improving the quality and periodicity of the structure. Based on the grown MQW structure, green VCSEL was fabricated. Lasing at 542 nm with 3 W output power was achieved at RT and 40 keV. The threshold was as low as 8 A/cm 2 .Introduction E-beam pumped vertical cavity surface emitting laser (VCSEL) is an efficient high power emission source perspective for display applications [1]. Output power up to 10 W at efficiency of 12 % in red range (645 nm) was achieved in a VCSEL with a resonant periodic gain using MOVPE grown GaInP/AlGaInP structures [2]. Lasing in green range was also achieved in VCSELs on MOVPE grown ZnCdSe/ZnSSe MQW structures [3,4]. But the penetration of Ga into the structure in a considerable distance from the GaAs/ZnSSe interface leads to the decrease of the nonequilibrium charge carrier transport from barrier layers into the QWs and to the increase of the laser threshold. Moreover the growth rate of the structure depends strongly on Ga content and this makes it difficult to obtain a strictly periodic structure. To avoid these problems, we removed the Ga-doped part of the MQW structure by chemical etching after removing the GaAs substrate [3]. However this method does not allow us to control the QW position inside the optical cavity. To achieve high efficiency of the laser it is very important to place QWs in the antinodes of the cavity mode being at gain maxima. Here we study other approaches to preventing Ga-doping of the long period ZnCdSe/ZnSSe MQW structures at the initial stage of epitaxy. By e-beam pumping, high energy electrons must pass through one of the cavity mirrors. This limits the mirror thickness which results in low reflectance and high cavity losses. Hence, to compensate all losses the number of QWs in the cavity is to be more than 20. To decrease the laser threshold, it is necessary to increase the thickness of the barrier layers separating the QWs up to the value comparable with the diffusion length of nonequilibrium carriers. This requirement together with positioning of QWs in the antinodes of the cavity mode defines the optimal thickness for ZnSSe barriers as about 0.2 µm.

Electron beam pumped lasers based on II–VI compound nanostructures from the visible to UVA

“…The first reason of such nonuniformity is a relaxation of internal strains accumulated in the structure during the extended growth process. Stimulation of the diffusion process during structure relaxation was observed in ZnCdSe/ZnSSe MQW structures [12]. However, in those structures, the QWs spread entirely while in the ZnSe/ ZnMgSSe structures only by a small amount.…”

Electron beam pumped light emitting devices

“…On the other hand, another international consortium explored electron beam pumped ZnSe-based lasers in a longitudinal configuration [89,90], more adequate for laser projection applications. The study covered blue (λ = 462 nm, quantum well material = ZnSe) and green (λ = 530 nm, quantum well material = ZnCdSSe) lasers.…”