Apart from a semiconductor substrate and a photosensitive region in the semiconductor substrate, which comprises a space charge zone region for generating a diffusion current portion and a diffusion region for generating a diffusion current portion, a photodiode includes an insulation means in the semiconductor substrate for at least partially confining the diffusion region against an adjacent surrounding region of the semiconductor substrate. The reduction of the bandwidth of photodiodes by the smearing of the response of the photodiode by the diffusion current is alleviated by providing an insulation means in the semiconductor substrate, which confines the diffusion region against the surrounding semiconductor substrate and hereby on the one hand reduces the number of charge carriers contributing to the diffusion portion by reducing the diffusion region, in which the diffusing charge carriers are generated, and on the other hand by “sucking off” diffusing charge carriers generated in the shrunk diffusion region by the insulation means, which is why same do not contribute to the photocurrent.
1. A photodiode, comprising:
a semiconductor substrate;
a photosensitive region in the substrate, the photosensitive region having a space charge zone region for generating a drift current portion and a diffusion region for generating a diffusion current portion; and
an insulator in the semiconductor substrate for at least partially confining the diffusion region from an adjacent surrounding region of the semiconductor substrate,
wherein the semiconductor substrate is of a first conduction type, and the space charge zone region is formed by a signal region with a second connectivity type in the semiconductor substrate, which is different from the fist conductivity type,
wherein the insulation means is formed by an insulation region of the second conductivity type in the semiconductor substrate at a predetermined spacing to the signal region, and
wherein the semiconductor substrate comprises a doping profile having a doping density decreasing in depth direction, such that a bulging of a space charge zone of the insulation region in lower regions of the semiconductor substrate results.
2. The photodiode of claim 1 , wherein the signal region comprises a comb structure.
3. The photodiode of claim 1 , wherein the predetermined spacing is smaller than the diffusion length of free charge carriers in the semiconductor substrate.
4. The photodiode of claim 1 , wherein the predetermined spacing ranges from 1 μm to 7 μm.
5. The photodiode of claim 1 , wherein the insulation region has a predetermined depth, which is greater than the depth of a signal region forming the space charge zone region by a predetermined multiple.
6. The photodiode of claim 5 , wherein the predetermined multiple is 2 to 10.
7. The photodiode of claim 1 , wherein the insulation region comprises several arms formed facing away from each other in star-shaped manner, each arm extending between the photosensitive region and further adjacent photosensitive regions being part of a photodiode array together with the photosensitive region.
8. The photodiode of claim 6 , wherein the insulator comprises further insulation regions also forming an array together, the insulation regions and photosensitive regions being arranged such that the photosensitive regions are individually formed in gaps formed by the arms of the insulation regions.
9. The photodiode of claim 1 , comprising a contacting conductor connected to the insulation region, for reading out a photocurrent generated in a space charge zone region formed by the insulation region.