frequency response of a diode greatly depends on the storage time of it.... at time periods near storage time there is no time for the diode to get reverse biased and hence the impedance starts dropping.....
there are lot of factors to be considered and that too when the technology changes new parameters that mattered less would often gain importance and hence there are many approximations and formulas for both impedance and inductance.....
if you need them then you would have to refer some ieee papers on diodes.....