Photoelectric conversion device with graded band gap and carrier concentration

Claim 1

A photoelectric conversion device comprising: a light absorbing region, made of non-monocrystalline material, for generating carriers in response to incident light; and a carrier multiplication region, made of non-monocrystalline material, said carrier multiplication region having opposed top and bottom sides spaced apart in a thickness direction of said carrier multiplication region, said carrier multiplication region being joined to said light absorbing region at said top side of said carrier multiplication region, wherein said carrier multiplication region comprises plural laminated layers, each said layer having respective opposed top and bottom sides spaced apart in said thickness direction, and each said layer, except for a top one of said layers adjacent to said light absorbing region, having its top side laminated to the bottom side of an adjacent one of said layers to form a respective heterojunction therebetween, wherein each said layer, when an electric field is applied to said device, has an energy band gap that increases gradually and continuously in a thickness direction away from said light absorbing region, each said layer being doped with a Group III element as an impurity, an impurity concentration in each said layer increasing gradually in the same direction as the increasing energy band gap so that the impurity concentration has a maximum value at a maximum energy band gap side and has a minimum value at a minimum energy band gap side, and a difference between a Fermi level and a vacuum energy level in the vicinity of each of the respective heterojunctions of said carrier multiplication region is substantially constant within in a range of 0.2 eV so that substantially no spikes and notches are formed in a valence band or a conduction band at the respective heterojunctions.