| 摘要 |
PROBLEM TO BE SOLVED: To obtain low noise characteristics by forming an InGaAs light absorption layer and forming a multiplication layer from a specified compsn. gradient layer the energy band of which continuously reduces away from the multiplication layer. SOLUTION: On an InP substrate 1 are laminated an n+ type InP buffer layer 2, nondoped n- type In1-x-yAlxGayAs comps. gradient multiplication layer 3, p-type InGaAs light absorption layer 5, p- type InP cap layer 6 and p+ type InGaAs contact layer 7, the compsn. gradient multiplication layer 3 is gradient from the InAlAs compsn. at the light absorption layer to the InGaAs compsn. at the n+ type buffer layer 2 and when this layer is applied, the collision ionization is facilitated by giving an additional electric field over 50 kV/cm to electrons and making a narrow gap at an ionizing region with electrons while an effective electric field applied to holes is set to about 200 kV/cm or less to suppress the collision ionization with holes, thereby realizing low noise characteristics.
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