Diode lasers operating in spectral range from 1.9 to 3.5 μm

Abstract

Mid-infrared lasers operating at room temperature (RT) in continuous wave (CW) mode are in demand for a variety of applications including laser detection and ranging, spectroscopy and infrared countermeasures. GaSb-based type-I quantum well (QW) diode laser technology addresses this demand providing compact lasers operating in spectral region from 1.9 to 3.4 µm, ex. [1,2,3]. The devices operate at voltages below 2 V and demonstrate RT CW power conversion efficiencies in excess of 25% near 2 µm and above 8 % at 3 µm [4]. These results show that Auger recombination does not preclude the CW RT operation of mid-infrared diode lasers. Low CW RT threshold current densities below 100 and 200 A/cm 2 obtained for 2 and 3 µm diode lasers, respectively revealed a bonus of the narrow bandgap QWs for laser development arising from the low density of states. This fundamental advantage became apparent in experiments after the optical and carrier confinement in active GaInAsSb QWs [5] were improved. This was achieved after the quaternary AlGaAsSb barrier material was replaced with the quinary AlGaInAsSb alloys [6]. In this work we report on progress in development of the metamorphic GaSb-based laser heterostructures and fabrication of the diffraction limited laser diodes.The utilization of a five component alloy enabled independent control over the valence and conduction band edge positions in the QW barrier and waveguide core materials. This flexibility allowed for design optimization that led to significant improvement of the device performance parameters and enabled fabrication of the first generation of the diode lasers operating at RT in CW at wavelength above 3 µm with hundreds of mW of output power. Similar flexibility in the design of the QWs is expected to open novel band engineering opportunities to optimize laser heterostructures for improved CW RT operation and extended wavelength range. One possible way to acquire this flexibility is to establish a growth technology that allows treating the lattice parameter of the device heterostructure as a design variable. This can be achieved by growing compositionally graded buffer layers to mediate the lattice mismatch between the substrate and the device heterostructure [7,8,9]. We designed and developed GaSb-based diode lasers grown onto GaInSb and AlGaInSb metamorphic buffers that increase the lattice constant by 1.6% above that of GaSb. The devices demonstrate high power RT operation with 200 mW of CW output power near 3 µm (Figure 1). The peculiarities of the metamorphic growth and potential to extend the operating wavelength, improve the device parameters and grow antimonide-based materials on GaAs will be discussed.The single spatial mode narrow ridge waveguide diode lasers were fabricated by both dry and wet etching techniques. We have developed two step selective wet etching methodology producing single spatial mode deep etched ridge waveguide lasers emitting above 100 mW CW in the 2 to 2.3 µm spectral region and above 15 mW CW near 3 µm. Experiment showed that the no...