Heavily-doped semiconductor lasers

A theoretical study of the effect of heavily doping the active layer of a semiconductor laser shows that the minority carrier density required to reach inversion decreases with increasing doping. Unfortunately, the minority carrier lifetime also decreases since there is a component of the recombination rate that is proportional to the doping density. It is found that for a dopant with a recombination rate coefficient
K_{B}, 5E-10
cm
³
/s (Zn in GaAs), the inversion current density has a local minimum at zero doping, but decreases again for n-type doping above
1E18
/cm, and is one third of the zero value at
4E18
/cm. The value of K
B
for other dopants and materials is unknown; however, for a dopant with a coefficient smaller than
5E-11
, the inversion current would be less than one tenth the zero value at
4E18
n-type, and would also decrease with the addition of p-type dopant. These results indicate that by heavily doping the active layer with the proper dopant, one might obtain both faster response and a lower threshold current, particularly with n-type dopants.