INNOVATIVE IV-VI LEAD SALTS QUANTUM WELL MID-INFRARED VERTICAL-CAVITY SURFACE-EMITTING LASERS

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

0080738 Shi The objective of this proposal is to develop innovative IV-VI mid-infrared vertical-cavity surface-emitting (VCSEL) lasers. Results from the first IV-VI VCSEL that the PI's recently demonstrated were very promising. Further research and development on such lasers could lead to continuous wave (cw) room temperature operation that will substantially advance the state of the art of mid-IR diode lasers to meet the application needs. Mid-infrared lasers have large market potential and high academic interests. Desired performance requirements for diode lasers that are not currently available include continuous wave (cw) operation at room temperature, spectral purity, and high output powers with good beam quality. The IV-VI quantum well devices to be studied under this proposal will have key advantages to meet these needs. Among narrow gap semiconductors, IV-VI materials such as PbSe have suppressed Auger non-radiative loss (by an order of magnitude over the best III-V quantum wells) and much lighter electron and hole masses that lead to further reduction of the lasing thresholds. Previously these have enabled lead salt lasers to set and maintain the records for maximum operating temperatures for both pulsed and cw operation among all mid-IR semiconductor diodes. They also provide advantages of wide temperature and current tuning because of the strong bandgap energy dependence on temperature. Especially exciting is the prospect of IV-VI quantum well (QW) vertical cavity surface emitting lasers (VCSELS) on BaF2 [111] substrates, which will have significantly improved heat dissipation, an excellent beam quality with a circular and near-diffraction-limited single-mode, very low threshold that could allow room temperature cw operation. High quality alternating BaF2 and Pbl-x SrxSe materials can be grown together. Because of the large contrast of refractive indices, distributed Bragg reflector (DBR) with only 3-pair quarter wavelength layers will provide reflectivity of nearly 100% with very broad bandwidth. Due to the broad DBR bandwidth, the alignment of the cavity resonance with the gain peak is not as difficult as in other semiconductor DBRs, which allows for a wide range of temperature tuning. Such broadband mirrors also eliminate mode hopping, reduce the fundamental lateral spread of the cavity mode and thus allow an extremely low threshold to be achieved. Recently the PI's have demonstrated the first IV-VI VCSELs and the initial results are very encouraging In the proposed research graduate students will be exposed to diverse experimental techniques and will develop an excellent grasp of cutting-edge technology. The combination of nano-scale material science, opto-electronics and processing technology provides an excellent opportunity for education. ***