Positron beam-aided characterization and optimization of post-growth defect passivation to enhance IR-detector operability.

Infrared photodetectors based on group III-V semiconductor materials pose great advantages due to their better characteristics, e.g., high mechanical strength, high chemical stability, outstanding performance at room temperature due to theoretically high carrier mobility, and low cost compared to those of HgCdTe-based detectors. As a result InAsSb became one of most important candidate for mid wavelength and InAsSbBi for mid to long wavelength infrared detector materials. However, the wavelength tune-ability of InAsSbBi suffers from non-optimal growth conditions, which results in defects. Defects ranging from Bi segregation, surface droplets, interstitials, and vacancy formation to dangling bonds can generate scattering centers and can be responsible for reduced carrier lifetime and higher dark current. JP Analytical, in collaboration with the University of Texas at Arlington (UTA) proposes to understand the nature of the defects and thereby attain an optimized passivation technique for such defects. During the Phase-I trial experiments, hydrogenation is found to be effective in passivating growth-related defects and increasing the carrier lifetime of InAsSbBi grown on GaSb substrate. While an un-optimized hydrogenation routine resulted in almost 4-times enhancement of the carrier lifetime, the upper limit to which the carrier lifetime of InAsSb-based martials can be increased still remains the main objective of this project. As such, hydrogenation, in general, will continue be used as a means of passivating defects to enhance the carrier lifetime and to reduce the dark current of the InAsSbBi-based IR detectors. The distinguishing facts of JP Analytical, however, come from the analytical capabilities and hydrogenation innovations. Positron beam-aided defects characterization in a depth-resolved manner will provide defect insight and evidence of passivation. Using a depth-resolved measurement of the Doppler broadening of the electron-positron annihilation radiation, it is possible to obtain selective information regarding charged open volume defects and the chemical environment of the defect site. Sensitivity to the chemical environment of the open volume defect becomes important when the neutral or charged vacancies get passivated by hydrogen. In Phase-II, the defect density characterized as such will be co-related with the amount of hydrogen intake necessary for optimized hydrogenation.  As the optimized Bi incorporation required higher growth temperature, hydrogenation defect passivation will be evaluated at optimized temperatures and pressure assisted by intense UV-photon source to thermally remove some of the unpassivated or unpinned defect centers without causing Bi to be segregated out of the solid solution. If successful, positron-beam aided characterization and hydrogenation can be commercialized for other materials systems that suffer non-optimal growth conditions to detect and pin down vacancies and passivate defects.