Abstract
We present the design of mid-infrared and THz quantum cascade laser cavities formed from planar photonic crystals with a complete in-plane photonic bandgap. The design is based on a honeycomb lattice, and achieves a full in-plane photonic gap for transverse-magnetic polarized light while preserving a connected pattern for efficient electrical injection. Candidate defects modes for lasing are identified. This lattice is then used as a model system to demonstrate a novel effect: under certain conditions - that are typically satisfied in the THz range - a complete photonic gap can be obtained by the sole patterning of the top metal contact. This possibility greatly reduces the required fabrication complexity and avoids potential damage of the semiconductor active region.
Highlights
Quantum cascade (QC) lasers are semiconductor laser sources based on intersubband (ISB) transitions in multiple quantum well systems [1]
In this paper we study the use of a connected honeycomb lattice for creating 2D photonic crystal QC laser structures
At an operating wavelength of 8 μm this results in a vertical mode overlap with the air holes of almost 90%. It is clear from this example why surface-plasmon QC lasers are ideally suited to photonic crystal (PC) technology; their reduced thickness allows for a significantly shallower etch of the semiconductor material in comparison to conventional laser waveguide structures in which an etch depth of 10 μm or more would be required in the mid-IR
Summary
Quantum cascade (QC) lasers are semiconductor laser sources based on intersubband (ISB) transitions in multiple quantum well systems [1]. Surface emission has been obtained, rather, by integrating second-order gratings on edge emitting devices [5, 6] or by replacing the standard Fabry-Perot cavity with a photonic crystal (PC) resonator [7, 8]. As is discussed in Ref.[14], for 2D photonic crystals, TM optical band gaps are favored in a lattice of isolated high-ε regions This configuration is incompatible with an electrical injection device due to its non-connected nature and an alternate approach is required. Below a certain critical waveguide thickness, a full photonic gap can be induced by the sole patterning of the metal layers This novel effect could be useful for the development of a variety of THz lasers, including PC surface-emitting lasers[16], due to the simple fabrication requirements
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