| 摘要 |
PURPOSE:To enable the light-absorbing efficiency to be increased without increasing the carrier generatin recombination noise, by providing a plurality of modulated-dope hetero junctions. CONSTITUTION:On a semiconductor substrate 1, a buffer layer 2, a first clad layer 3, a first light-absorbing layer 4, a second clad layer 5, a second light- absorbing layer 6, a third clad layer 7, an electrode forming layer 8, a light- absorbing window 1, etc., are formed. With this arrangement, since there are differences between the layers 3, 5 and 7 and the layr 4, 6 in terms of te dorbidden band width an the optical impurity carrier density, an internal electric field is generated in the light-absorbing layer in the vicinity of each of the modulated - dope hetero junctions. The light entering the element through the window 11 is absorbed by each of the layer 4 and 6 to produce whole-electron pairs. These pairs, however, travel through the absorbing layers 4, 6 while being spatially separated from each other. Accordingly, the carrier generation recombination noise can be made exceedingly small. The light-absorbing efficiency is increased by further laying thick light-absorbing layers in accordance with the modulated- dope double-hetero junction structure. Thus, the noise level is greatly lowered, and high sensitivity is obtained. |
