Forward-bias impedance of GaAs 1-xP x LED's

The forward bias impedance characteristics of GaAs _{1- x}P _x LED's have been determined. In all cases, the equivalent parallel capacitance reaches a maximum and then either saturates ( x = 0.4) or becomes negative at certain frequencies ( x = 0.85 and x = 1). The current densities at which C_p maxima are reached are below typical values for display, multiplexing or optical emitters applications (i.e. J_F = 1 A/cm ² for x = 0.85). It is suggested large series resistances for x = 0.4, and conductivity modulation effects for x > 0.4 are responsible for the above impedance behavior.