Volume 86, Issue 2, 15 July 1999
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Differential gain, differential index, and linewidth enhancement factor for a 4 μm superlattice laser active layer86(1999); http://dx.doi.org/10.1063/1.370793View Description Hide Description
We describe temporally and spectrally resolved measurements of the material differential gain, differential refractive index, and linewidth enhancement factor for a multilayersuperlattice intended for use in midwave-infrared semiconductor lasers. We find good agreement between measured quantities and theoretical predictions based on a superlatticeK⋅p formalism. The superlattice was designed for suppression of Auger recombination and intersubband absorption, and we find that the strategies employed in this process result in other characteristics that are desirable in a semiconductor laser gain medium. Specifically, for carrier densities and wavelengths appropriate to threshold in an optimized cavity configuration, this structure has a differential gain of approximately a value comparable to that reported for near-infrared strained quantum wells. The peak gain and peak differential gain are nearly spectrally coincident, leading to a small value for the differential index. The large differential gain and small differential index result in a linewidth enhancement factor of less than one. This indicates that filamentation in high-power lasers based on this superlattice should be suppressed and that this structure is attractive for use in midwave-infrared lasers designed for spectrally pure operation.
86(1999); http://dx.doi.org/10.1063/1.370794View Description Hide Description
This article investigates distributed Bragg reflectors(DBRs) based on two wide-gap II–VI semiconductor alloy combinations: ZnMgSe/ZnCdSe and ZnMgSe/ZnSeTe. Prior to fabrication of the DBRs, a prism coupler technique was used to determine the indices of refraction n of the above ternary alloys of various compositions prepared by molecular beam epitaxy(MBE). Using these values of n, two DBR systems, and were fabricated, each with a relatively large difference in the indices of refraction between its layer materials. It was found that although a higher reflectivity could be achieved using the ZnMgSe/ZnSeTe combination (since it manifests a larger difference in their indices of refraction the number of periods which can be deposited in this DBR system is limited due to growth difficulties that arise when combining ZnMgSe and ZnSeTe. Therefore the ZnMgSe/ZnSeTe DBR system, which was restricted to just 10 periods, yielded a modest reflectivity of 85%. On the other hand, although in the ZnMgSe/ZnCdSe DBR system is smaller it poses fewer growth difficulties, making it possible to grow DBR stacks consisting of a large number of layers without compromising the crystal quality of the structure. By growing 20 periods of the ZnMgSe/ZnCdSe DBR system, we obtained a DBR with a reflectivity as high as 98%.