In a light-emitting double-heterojunction structure, interface recombination reduces the quantum efficiency of spontaneous emission

; more specifically, in a double-heterojunction laser this increases the threshold current density J
th. Simplified expressions are derived here for the dependence of

and J
thon interface recombination velocities in the injection regimes of both

(or

) and

. Easy-to-handle criteria are presented for checking the validity of the simplifications when using these expressions for evaluating the recombination velocities from experimental data.