Effect of free-carrier concentration and optical injection on carrier lifetimes in undoped and iodine doped CdMgTe/CdSeTe double heterostructures grown by molecular beam epitaxy

摘要

Time-resolved and time integrated photoluminescence (PL) studies are reported for undoped and doped CdMgTe/CdSeTe double heterostructures (DHs) grown by molecular beam epitaxy. Undoped DHs are studied with absorber layer thickness varying from 0.5 to 2.5 mu m. The n-type free-carrier concentration is varied similar to 7 x 10(15), 8.4 x 10(16), and 8.4 x 10(17) cm(-3) using iodine as a dopant in different absorber layer thicknesses (0.25-2.0 mu m). Optical injection is varied from 1 x 10(10) to 3 x 10(11) photons/pulse/cm(2), corresponding to the initial injection of photo-carriers up to similar to 8 x 10(15) cm(-3), to examine the effects of excess carrier concentration on the PL lifetimes. Undoped DHs exhibit an initial rapid decay followed by a slower dependence with carrier lifetimes up to similar to 485 ns. The dependence of carrier lifetimes on the thickness of the absorber layers (0.5-2.5 mu m) suggests interface recombination velocities (v(int)) similar to 1288 and 238 cm s(-1) in the initial and later decay times, respectively, corresponding to high and low photo-carrier concentrations. The Shockley-Read-Hall model is used to describe the results in which variations are observed in v(int) for undoped DHs. The lifetimes of doped DHs show a consistent trend with thickness. The v(int) similar to 80-200 cm s(-1) is estimated for doping n similar to 7 x 10(15) cm(-3) and 240-410 cm s(-1) for n similar to 8.4 x 10(16) cm(-3). The observed decrease in carrier lifetimes with increasing n is consistent with growing importance of the radiative recombination rate due to the excess carrier concentration. The effect of carrier concentration on the PL spectrum is also discussed.