Minority carrier radiative lifetime

Radiative recombination of minority carriers is tlie most likely process in direct gap semiconductors. Since tlie carriers at tlie CB minimum and tlie VB maximum have tlie same momentum, very fast recombination can occur. The radiative recombination lifetimes in direct semiconductors are tlius very short, of tlie order of tlie ns. The presence of deep-level defects opens up a non-radiative recombination patli and furtlier shortens tlie carrier lifetime. 

The situation is very different in indirect gap materials where phonons must be involved to conserve momentum. Radiative recombination is inefficient, resulting in long lifetimes. The minority carrier lifetimes in Si reach many ms, again in tire absence of defects. It should be noted tliat long minority carrier lifetimes imply long diffusion lengtlis. Minority carrier lifetime can be used as a convenient quality benchmark of a semiconductor. 

N. K. Dutta, Radiative Transitions in GaAs and Other III-V Compounds R. K. Ahrenkiel, Minority-Carrier Lifetime in III-V Semiconductors T. Furuta, High Field Minority Electron Transport in p-GaAs M. S. Lundstrom, Minority-Carrier Transport in III-V Semiconductors R A. Abram, Elfects of Heavy Doping and High Excitation on the Band Structure of GaAs D. Yevick and W. Bardyszewski, An Introduction to Non-Equilibrium Many-Body Analyses of Optical Processes in III-V Semiconductors... 

In the limit where there is no nonradiative recombination, which means that 1/Tnonrad IS zero, the radiative efficiency becomes unity. The lifetime of excess minority carriers can be obtained by measuring the dynamic behaviors of optical emissions involved using time-resolved photoluminescence (TRPL). 

Radiative reeombination of minority earriers is the most likely proeess in direet gap semieonduetors. Sinee the carriers at the CB minimum and the VB maximum have the same momentum, very fast reeombination ean oeeur. The radiative reeombination lifetimes in direet semieonduetors are thus very short, of the order of the ns. The presence of deep-level defeets opens up a non-radiative reeombination path and further shortens the earrier lifetime. 

---