Optical Characterization of Iv-VI Mid-Infrared Vcsel
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OPTICAL CHARACTERIZATION OF IV-VI MID-INFRARED VCSEL F. Zhao, H. Wu, T. Zheng, P. J. McCann, A. Majumdar, Lalith Jayasinghe and Z. Shi School of Electrical and computer Engineering 202 West Boyd, University of Oklahoma, Norman, OK 73019
ABSTRACT PbSe/PbSrSe multiple-quantum-well (MQW) structures and PbSrSe thin films were grown on BaF2 (111) substrates by molecular beam epitaxy (MBE) and characterized by Fourier transform infrared (FTIR) spectrometer. Strong photoluminescence without Fabry-Perot interference fringes was observed even at room temperature from the MQW structures. The peak energies for the MQW structures with different well widths shifted to high energy with increasing temperature. The absorption edge of PbSrSe layer was determined by transmission spectra. Meanwhile, we designed and fabricated λ=4.1 µm MQW vertical cavity surface emitting laser (VCSEL). A power output of 40 mW was obtained at room temperature. The room temperature threshold pump density is 200 kW/cm2.
INTRODUCTION Mid-infrared diode lasers are mainly used for trace-gas-sensing applications [1]. This is due to the fact that the numerous absorption lines of many gaseous molecules, such as CO2 , CH4 , N2 O, HCl, etc., are in the range of mid-infrared spectra. Performance requirements that are not yet available include continuous wave (cw) operation at thermoelectric cooler range (T ≥ 240 K), spectral purity, and reasonable output powers (≥1 mW) with good beam quality. Although substantial advances have been made in the development of edge emitting mid-infrared diode lasers, including IV-VI lead-salt [2], quantum cascade (QC) [3,4] and type-II quantum well (QW) devices [5], there has little progress until recently in developing mid-IR vertical cavity surface emitting laser (VCSEL). This is despite the attractive performances of VCSELs, such as low-divergence circular beams, single mode operation, and the high possibility of twodimensional monolithic integration arrays. It is well known that the presence of the Auger recombination in narrow gap semiconductors is the major factor limiting high temperature operation of mid-infrared lasers. The major advantage of lead salt materials is that the Auger coefficients are more than one or two orders of magnitude lower than other mid-IR materials with a comparable bandgap [6,7], and it will not prevent quantum structure of these materials from achieving room temperature laser operation [6]. We proposed and demonstrated the first IV-VI VCSEL on BaF2 (111) substrate [8]. Such VCSELs have obtained near-room-temperature pulsed operation 300mW output power [9,10] and threshold density as low as 10.5 kW/cm2 [11]. In this paper, we report optical characterization of IV-VI PbSe/PbSrSe MQW structures and PbSrSe layer for VCSEL. The optical properties of the VCSEL are also given.
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EXPERIMENTAL DETAIL The PbSe/PbSrSe MQW structures and PbSrSe thin films were grown on BaF2 (111) substrates by molecular-beam epitaxy (MBE) in an Intevac Modular Gen II system using compound sources for PbSe and BaF2 , a
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