Terahertz Laser Diodes Display Single-Mode Operation

Daniel S. Burgess

Researchers at the National Enterprise for nanoScience and nanoTechnology and Scuola Normale Superiore, both in Pisa, Italy; and at Cambridge University and at the University of Leeds, both in the UK, have fabricated distributed feedback quantum cascade lasers operating in the terahertz range that display single-mode operation and peak output powers of up to 1.8 mW. They suggest that the work may have applications in the development of terahertz lasers for spectroscopy related to astronomical and atmospheric sensing.

In the 4.34- and 4.43-THz devices, the distributed feedback region comprises a 220-nm-deep grating in doped GaAs, on the crests of which the researchers deposited and annealed GeAu/Au ohmic contacts. The contacts introduce an additional loss modulation that mitigates spatial hole burning effects and increases mode discrimination, enabling single-mode operation with a side mode suppression ratio of better than 20 dB.

At an operating temperature of 5 K, a distributed feedback quantum cascade laser with a 9.2-µm grating period displayed a slope efficiency of 13 mW/A. Output powers of 700 µW were obtained from the emitter at temperatures as high as 50 K.