the photodiodes can be decreased and crosstalk between the photodiodes can be reduced also disclosed is an optical receiver device including the photodiode array application_number US 36824603 A description the embodiments of the present invention will be described with reference to the drawings in the drawings the same elements are represented by the same reference numerals and duplication of description is avoided it is to be understood that the dimensional proportions of the individual elements in the drawing do not necessarily correspond to the actual proportions 0032 fig1 a is a plan view of a photodiode array of the present invention and fig1 b is a cross sectional view of the photodiode array shown in fig1 a fig2 is an equivalent circuit diagram of the photodiode array shown in fig1 a and 1 b fig3 is an enlarged view of the photodiode array shown in fig1 a and 1 b and fig4 is an enlarged view which shows a variation of the photodiode array shown in fig3 on a fe doped semi insulative inp substrate 10 an n type inp layer 11 an ingaas layer light receiving layer 12 and an inp layer window layer or cap layer 13 are grown in that order from the bottom all of the n type inp layer 11 the ingaas layer 12 and the inp layer 13 are circular and the ingaas layer 12 and the inp layer 13 have a smaller diameter than that of the n type inp layer 11 a p type.