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Recent advance in semiconductor mid-infrared lasers emitting at 3-12 µm

Razeghi M.

Opto-Electronics Review

1999

Vol. 7, No. 1

29-58

In this article, we discusses existing state-of-the-art techniques for the design and fabrication of mid-wave infrared semiconductor lasers (3 µm < ʎ < µm). Although historically Pb-salt-based lasers had been studied intensively, at the present moment III-V semiconductor lasers are the only viable solution for high power generation of infrared light (P > 300 mW), and thus we focus our study mostly on lasers based on III-V compound semiconductors. Currently, three types of semiconductor lasers are extensively studied in the literature : lasers employing type I interband transition, type II superlattice, and intersubband transitions. Type I interband lasers employing InAsSb/InPAsSb/InAs or InGaAsSb/AlGaAsSb material systems have been most widely studied so far as this type of lasers requires relatively simple and strainghtforward structures for crystal growth and fabrication. Peak optical output power up to 3 W has been demonstrated for ʎ > 3,4 µm at 90 K from InAsSb/InAsSbP double heterostructure semiconductor lasers grown by low - pressure metalorganic chemical vapour deposition. Currently, the high - power operation (> 300 mW) for ʎ > 3 µm from type I interband semiconductor lasers is typically limited to low operating temperatures (bellow 150 K). Besides Auger recombination which is arguably the major reason for this high temperature sensitivity, the main difficulty in the (Ga) InAsSb - based lasers is the material composition fluctuation associated with large immiscibility gap of the (Ga) InAsSb alloys and the resulting atomic phase separation, which causes spatial inhomogeneity. The effect of the composition fluctuations is formulated in detail. Physical models for emission wavelength, far-field and threshold current are developed and compared with experiment, and magnitude of composition fluctuation is estimated. Room temperature operation for ʎ > 3,5 µm was achieved from intersubband Quantum Cascade Lasers (QCL) in pulse operation with peak power over 700 mW at 90 K. Yet low quantum efficiency due to fast phonon-related carrier lifetime makes cw operation difficult to perform at the present. We discuss general physical principles, design rules for intersubband QCL are described as well as recent experimental advances. Superlattice mini-band structure, carrier-transport in the presence of electric field will be discussed. Finally we discuss the physical mechanisms and design principles crucial for the device fabrication of bipolar and unipolar type II interband lasers. A more complicated band model should be used compared to intersubband cascade lasers because both wavefunctions of electrons and holes should be considered. Carrier-transport in the presence of electric field will be discussed.