Spectral Characteristics of Half-Ring Quantum-Cascade Lasers
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R PHYSICS AND LASER OPTICS
Spectral Characteristics of Half-Ring Quantum-Cascade Lasers A. V. Babicheva, *, D. A. Pashnevb, c, A. G. Gladysheva, A. S. Kurochkina, E. S. Kolodeznyia, L. Ya. Karachinskya, d, e, I. I. Novikova, d, e, D. V. Denisovf, V. V. Dudeleve, G. S. Sokolovskiie, D. A. Firsovb, L. E. Vorob’evb, S. O. Slipchenkoe, A. V. Lutetskiye, N. A. Pikhtine, and A. Yu. Egorova a ITMO
b
University, St. Petersburg, 197101 Russia Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia c Center for Physical Sciences and Technology, Vilnius, LT-10257 Lithuania d Connector Optics LLC, St. Petersburg, 194292 Russia e Ioffe Institute, St. Petersburg, 197101 Russia f St. Petersburg Electrotechnical University “LETI,” St. Petersburg, 197376 Russia *e-mail: [email protected] Received January 9, 2020; revised March 16, 2020; accepted April 15, 2020
Abstract—A cavity scheme based on a half-ring with different radii is proposed and fabricated for 7–8 μm quantum-cascade lasers. A quantum-cascade laser with a half-ring cavity radius of 191 μm demonstrated lasing with a spectral width of 474 nm (82 cm–1) at low temperatures. The free spectral range in these lasers was determined by the whispering gallery modes typical for ring cavities. The laser bandwidth at room temperature was 190 nm (31 cm–1), which may be related to an increase in the internal losses with increasing temperature. An increase in the cavity radius to 291 μm made it possible to achieve room-temperature lasing with whispering gallery modes and a bandwidth of 249 nm (40 cm–1) by reducing losses on the mirrors. Keywords: superlattice, quantum-cascade lasers, epitaxy, indium phosphide, half-ring resonator DOI: 10.1134/S0030400X20080068
INTRODUCTION Today, the literature provides the results of development of microdisk quantum-cascade lasers (QCLs) [1–6], QCL cavities in the form of elongated ellipses (chaotic resonators) [7–9], lasers based on Pascal’s limacons [10], and ring cavities [11]. Moreover, there are studies on fabrication of ring surface-emitting QCLs with distributed feedback (DFB) on the semiconductor surface [12–25]. As was reported in [1], the advantage of using the ring geometry in QCLs is the absence of contribution of surface recombination to charge carrier transport (due to unipolarity of QCLs, which operate on the principle of electron transport). In the present work, we report the results of investigation of 7–8 μm half-ring QCLs with a wide emission spectrum. EXPERIMENTAL The QCL heterostructure was grown by Connector Optics LLC using a Riber 49 molecular-beam epitaxy system [26, 27]. As substrates, (001)-oriented InP wafers doped with sulfur to n = 1.0 × 1017 cm–3 were used. The active region included 50 cascades based on double-phonon depopulation of the lower level [28–
30]. The cascades were formed using the In0.53Ga0.47As/In0.52Al0.48As heteropair. The upper waveguide cladding (InP layer) was 3.9 μm thick (n = 1.0 × 1017 cm–3). The In0.53Ga0.47As contact layers were 100 and 20 nm thick with dopi
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