Patent ID: 7307290

Claim:
A compound semiconductor wafer comprising: an InP substrate; a multi-layered structure consisting of a plurality of step layers comprising InAs x P 1-x arranged successively on said substrate; a buffer layer comprising InAs y P 1-y arranged on said multi-layered structure, with said multi-layered structure between said buffer layer and said substrate; and a light receiving layer comprising In z Ga 1-2 As arranged on said buffer layer, with said buffer layer between said light receiving layer and said multilayered structure; wherein: said step layers include at least a first step layer ( 12 a ), a second step layer ( 12 b ) and a third step layer ( 12 c ) arranged successively in order between said buffer layer and said substrate with said first step layer ( 12 a ) relatively closer to said buffer layer and said third step layer ( 12 c ) relatively closer to said substrate; respective interfaces ( 30 a , 30 b , 30 c , 30 d ) comprising InAs x P 1-x are formed between said buffer layer and said multi-layered structure, and between successive ones of said step layers; said interfaces include a first interface ( 30 a ) on a side of said first step layer ( 12 a ) facing toward said buffer layer, a second interface ( 30 b ) between said first step layer ( 12 a ) and said second step layer ( 12 b ), and a third interface ( 30 c ) between said second step layer ( 12 b ) and said third step layer ( 12 c ); among said first, second and third step layers, said first step layer has a relatively highest value of said x, said second step layer has a middle value of said x, and said third step layer has a relatively lowest value of said x of said InAs x P 1-x ; said y of said InAs y P 1-y of said buffer layer is higher than said relatively highest value of said x of said first step layer; and a value of said x of said InAs x P 1-x in said first interface ( 30 a ) is lower than said middle value of said x of said second step layer ( 12 b ), and/or a value of said x of said InAs x p 1-x in said second interface ( 30 b ) is lower than said relatively lowest value of said x of said third step layer ( 12 c ).