This paper describes the properties of Ge1-ySny light emitting diodes with a broad range of Sn concentrations (y=0.0-0.11). The devices are grown upon Si(100) platforms using ultra-low temperature deposition of highly reactive Ge and Sn hydrides. The device fabrication adopts two new photodiode designs which lead to optimized performance and enables a systematic study of the effects of strain relaxation on emission efficiency. In contrast with n-Ge/i-Ge1-ySny/p-Ge analogs, which in most cases contain two defected interfaces, our designs include a p-layer with composition Ge1-zSnz chosen to be z<y to facilitate light extraction, but with z close enough to y to guarantee no strain relaxation at the i/p interface. In addition, a Ge1-xSnx alloy is also used for the n layer, with compositions in the 0≤x≤y range, so that defected and non-defected n/i interfaces can be studied. The electroluminescence spectra vs the Sn content y in the intrinsic layer of the diodes exhibit a monotonic shift in the emission wavelength from 1550nm to 2500nm. On the other hand, the emission intensities show a complex dependence that cannot be explained solely on the basis of Sn concentrations. Detailed theoretical modeling of these intensities makes it possible to extract recombination lifetimes that are found to be more than three times longer in samples in which strain relaxation has not occurred at the n-i interface, demonstrating the existence of a large non-radiative contribution from the relaxation defects. This finding is particularly significant for direct gap diodes with y>0.09, for which it is practically impossible to avoid strain relaxation in n-Ge/i-Ge1-ySny/p-Ge analogs. The new designs introduced here open the door to the fabrication of highly efficient electrically pumped systems for applications in future generations of integrated photonics.
ASJC Scopus subject areas
- Physics and Astronomy(all)