Patent ID: 7259439

Claim:
A semiconductor photodetector comprising: a semi-insulating substrate having an upper step surface, a middle step surface, and a lower step surface with their respective heights different from each other in a top surface portion, the lower step surface being located between the upper step surface and the middle step surface in a lateral direction, wherein a side wall forming a boundary between the lower step surface and the upper surface being inclined so as to form an acute angle between the side wall and the lower step surface; a first semiconductor layer formed immediately above the lower step surface, having a first top surface portion of a flat surface shape with a height equal to that of the middle step surface and a second top surface portion with a height equal to or higher than that of the first top surface portion, and comprising a first impurity; a second semiconductor layer formed above the second top surface portion of the first semiconductor layer, having a top surface portion of a flat surface shape with a height equal to that of the upper step surface, and comprising a second impurity; a first electrode provided astride and above the first top surface portion of the first semiconductor layer and the middle step surface of the semi-insulating substrate; and a second electrode provided astride and above the top surface portion of the second semiconductor layer and the upper step surface of the semi-insulating substrate.