Front-illuminated-type photodiode array

1. A front-illuminated-type photodiode array comprising:

(a) a first-electroconductive-type semiconductor substrate;

(b) a first-electroconductive-type electrode placed at the rear-face side of the semiconductor substrate;

(c) a first-electroconductive-type absorption layer that:

(c1) is formed at the front-face side of the semiconductor substrate; and

(c2) has an absorption edge wavelength of λ gr ;

(d) a plurality of lightwave receiving parts comprising:

(d1) a plurality of second-electroconductive-type regions formed from the surface of the absorption layer to a certain distance into the absorption layer such that the regions are arranged one- or two-dimensionally; and

(d2) a second-electroconductive-type electrode provided at a part of each of the second-electroconductive-type regions;

(e) an antireflective coating that:

(e1) covers the top surface other than the individual second-electroconductive-type electrodes; and

(e2) is for preventing the reflection of an incoming lightwave;

(f) at least one first-electroconductive-type leakage-lightwave-absorbing layer that:

(f1) is provided between the first-electroconductive-type electrode and the absorption layer; and

(f2) has an absorption edge wavelength, λ ga , equal to or longer than the absorption edge wavelength, λ gr , of the absorption layer (λ gaγ ≧λ gr ); and

(g) a first-electroconductive-type buffer layer that:

(g1) is provided between the absorption layer and the at least one leakage-lightwave-absorbing layer; and

(g2) has an absorption edge wavelength, λ gb , shorter than the absorption edge wavelength, λ gr , of the absorption layer (λ gb <λ gr ).

2. A front-illuminated-type photodiode array as defined by claim 1 , the array further comprising a window layer that:

(a) is provided on the absorption layer; and

(b) has an absorption edge wavelength, λ gw , shorter than the absorption edge wavelength, λ gr , of the absorption layer (λ gw <λ gr );

the second-electroconductive-type regions penetrating through the window layer.

3. A front-illuminated-type photodiode array as defined by claim 1 , the array further comprising a window layer that:

(a) is provided on the absorption layer; and

(b) has an absorption edge wavelength, λ gw , shorter than the absorption edge wavelength, λ gr , of the absorption layer (λ gw <λ gr );

the second-electroconductive-type regions penetrating through the window layer.

4. A front-illuminated-type photodiode array as defined by claim 3 , wherein the at least one leakage-lightwave-absorbing layer, the buffer layer, the absorption layer, and the window layer are formed on the semiconductor substrate by epitaxial growth.

5. A front-illuminated-type photodiode array comprising:

(a) an n-type InP substrate;

(b) a common n-electrode provided at the rear side of the n-type InP substrate;

(c) an n-type InGaAs leakage-lightwave-absorbing layer epitaxially grown at the front side of the n-type InP substrate;

(d) an n-type InP buffer layer epitaxially grown on the n-type InGaAs leakage-lightwave-absorbing layer;

(e) an n-type InGaAs absorption layer epitaxially grown on the n-type InP buffer layer;

(f) an n-type InP window layer epitaxially grown on the n-type InGaAs absorption layer;

(g) a plurality of p-regions that:

(g1) are formed so as to penetrate through the n-type InP window layer and extend into the n-type InGaAs absorption layer to a certain extent; and

(g2) are arranged one- or two-dimensionally;

(h) a p-electrode provided at a part of each of the top faces of the p-regions; and

(i) an antireflective coating that covers the top surface other than the individual p-electrodes;

the n-type InGaAs leakage-lightwave-absorbing layer having an absorption edge wavelength equal to or longer than that of the n-type InGaAs absorption layer.

6. A front-illuminated-type photodiode array comprising:

(a) an n-type InP substrate;

(b) a common n-electrode provided at the rear side of the n-type InP substrate;

(c) an n-type InGaAs leakage-lightwave-absorbing layer epitaxially grown at the front side of the n-type InP substrate;

(d) an n-type InP buffer layer epitaxially grown on the n-type InGaAs leakage-lightwave-absorbing layer;

(e) an n-type InGaAs absorption layer epitaxially grown on the n-type InP buffer layer;

(f) a plurality of p-regions that:

(f1) are formed from the surface of the n-type InGaAs absorption layer to a certain distance into the absorption layer; and

(f2) are arranged one- or two-dimensionally;

(g) a p-electrode provided at a part of each of the top faces of the p-regions; and

(h) an antireflective coating that covers the top surface other than the individual p-electrodes;

the n-type InGaAs leakage-lightwave-absorbing layer having an absorption edge wavelength equal to or longer than that of the n-type InGaAs absorption layer.