Depletion layer thickness?

Hi, all

Does anybody know how large is depletion layer width for photodiode?

For example, for photodiode S3590-06, which has cut-off frequency of 20MHz, and its depletion layer width is 500um.

But what about the other photodiode, for example, a photodiode with 100MHz or 50MHz?

I know, with increase the bandwidth, the depletion layer should be reduced to give a fast transit time.

But is there a formula or a rule of thumb says that at each cut-off frequency what is the depletion layer width should be fabricated.

For example, with 100MHz, 50um should be use, for 1GHz, 10um is proffered.

Thanks all
--------------------------------

If there is not such formula, may somebody tell me what is typical depletion layer width for 25M 50M and 100MHz photodiode.