Comparison of Lasing Characteristics of GaInNAs Quantum Dot Lasers and GaInNAs Quantum Well Lasers
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Comparison of Lasing Characteristics of GaInNAs Quantum Dot Lasers and GaInNAs Quantum Well Lasers
C. Y. Liu, S. F. Yoon, and Z. Z. Sun School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore, 639798 ABSTRACT
Self-assembled GaInNAs/GaAsN single layer quantum dot (QD) lasers grown using solid source molecular beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. High-temperature operation up to 65°C was demonstrated from an unbonded GaInNAs QD laser (50 × 1060 µm2), with high characteristic temperature (T0) of 79.4 K in the temperature range of 10-60°C. For comparison, temperature-dependent operation has also been studied on the GaInNAs single quantum well (SQW) lasers. Unlike the relation between the cavity length and T0 in GaInNAs SQW lasers, longer-cavity GaInNAs QD laser (50 × 1700 µm2) showed lower T0 of 65.1 K, which is presumably believed due to the nonuniformity of the GaInNAs QD layer. INTRODUCTION
Recently, there has been considerable research interest in GaInNAs material grown on GaAs substrates, for realizing low-cost, high-performance and high-temperature laser diodes in the 1.3µm wavelength regime [1-10]. So far, GaInNAs quantum well (QW) laser performance has been improved significantly [1-5]. Meanwhile, studies on GaInNAs quantum dot (QD) structures have also attracted much attention [6-10], since QD structures, with three-dimensional carrier confinement, are anticipated to have many advantages over their QW counterparts, such as decreased transparency current density (Jtr), increased differential gain, high characteristic temperature (T0), and largely extended emission wavelength [11]. Moreover, in the case of GaInNAs QD lasers, reduction of bandgap energy with N incorporation decreases the dot sizes for long wavelength emission. Smaller dots have larger sub-band energy difference, resulting in suppression of carrier leakage to high energy states. Furthermore, smaller dot sizes are also advantageous for obtaining high QD density [9]. GaInNAs QDs have been successfully grown using molecular beam epitaxy (MBE) [6, 7], chemical beam epitaxy (CBE) [8, 9], and metal organic chemical vapor deposition (MOCVD) [10]. Photoluminescence (PL) emission in the 1.3 and 1.5 µm region from MBE-grown GaInNAs QDs at room temperature (RT) has been demonstrated, which means the fabrication of 1.3 and 1.55 µm GaInNAs QD lasers becomes feasible [6]. However, compared with a large amount of research on GaInNAs QW lasers [1-5], relatively fewer results on GaInNAs QD lasers have been reported [7, 8, 10]. Makino et al. first reported pulsed lasing from a CBE-grown Ga0.5In0.5N0.01As0.99 QD laser at 77 K with emission wavelength of 1.02 µm and threshold current density (Jth) of 1.9 kA/cm2 [8]. More recently, Gao et al. [10] reported the first MOCVD-grown GaInNAs QD ridge waveguide (RWG) laser (4 × 800 µm2) emitting at 1078 nm under RT,
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pulsed operation with Jt
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