RECOMBINATION DYNAMICS IN QUANTUM WELL SEMICONDUCTOR STRUCTURES (GALLIUM-ARSENIDE, PHOTOLUMINESCENCE, RADIATIVE, TIME-RESOLVED ALUMINUM)

Time-resolved and time-integrated photoluminescence as a function of excitation energy density have been observed in order to study recombination dynamics in GaAs/Al(,x)Ga(,1-x)As quantum well structures. The study of room temperature photoluminescence from the molecular beam epitaxy (MBE)-grown multiple quantum well structure and photoluminescence peak energy as a function of tem- perature shows that room temperature recombination at excitation densities above the low 10('16) cm('-3) level is due to free carriers, not excitons. This is the first study of time-resolved photoluminescence of impurities in quantum wells; data taken at different emission wave- lengths at low temperatures shows that the impurity-related states at photon energies lower than the free exciton peaks luminesce much more slowly than the free exciton states.; Results from a similar structure grown by metal-organic chemical vapor deposition (MOCVD) are explained by saturation of traps. An unusual increase in decay rate observed tens of nanoseconds after excitation is probably due to carriers falling out of the trap states. Since this is the first study of time-resolved photoluminescence of MOCVD-grown quantum well structures, this unusual behavior may be realted to the MOCVD growth process. Further investigations indi- cate that the traps are not active at low temperatures; they become active at approximately 150 K. The traps are probably associated with the (hetero)interfaces rather than the bulk Al(,x)Ga(,1-x)As material. The 34 K photoluminescence spectrum of this sample revealed a peak shifted down by approximately 36 meV from the main peak. Time-resolved and time-integrated photoluminescence results here show that this peak is not a stimulated phonon emission sideband, but rather is an due to an acceptor impurity, probably carbon. Photo- luminescence for excitation above and below the barrier bandgap shows that carriers are efficiently collected in the wells in both single and multiple quantum wells structures. The funnel design of the single quantum well laser led to high carrier densities, favoring radiative recombination and saturating traps efficiently.; Both the MBE and MOCVD results indicate that the bimolecular radiative recombination coefficient(, )B < 10('-10) cm('3)/sec, smaller than originally expected for quantum wells and probably smaller that the value for bulk GaAs.