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US 6,477,283 B1Granted
Electroabsorption optical modulator and fabrication method thereof
AssigneeNEC Corporation
InventorsJunichi Shimizu, Yuji Furushima
Life of this patent
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Abstract
An impurity diffusion preventing layer is provided between a first upper clad layer adjacent to an optical absorption layer and a second upper clad layer provided on the first upper clad layer in order to prevent p type impurity from diffusing to the first upper clad layer adjacent to the optical absorption layer.
Claims10
An electroabsorption type optical modulator comprising:
- a striped waveguide constructed with a multi-layered structure formed on a semiconductor substrate such that an optical absorption layer is sandwiched between clad layers having band gap energy larger than that of said optical absorption layer, so that absorption of light incident on one edge of said optical absorption layer is changed by changing strength of electric field applied to said optical absorption layer;
- an impurity diffusion preventing layer provided between a first upper clad layer adjacent to an upper surface of said optical absorption layer and a second upper clad layer, said impurity diffusion preventing layer being adapted to prevent p type impurity from diffusing from said second upper clad layer;
- and a semiconductor layer provided above said second upper clad layer to said first upper clad layer.
A fabrication method for fabricating an electroabsorption type optical modulator formed on a semiconductor substrate of a first conductivity type, comprising the step of:
- forming a waveguide having a striped multi-layered structure including a lamination of at least a lower clad layer of the first conductivity type, a non-doped optical absorption layer having band gap energy smaller than that of said lower clad layer, a first upper clad layer having band gap energy larger than that of said optical absorption layer and smaller than that of said lower clad layer, an impurity diffusion preventing layer of a second conductivity type having band gap energy larger than that of said first clad layer and carrier concentration lower than that of said first upper clad layer and a second upper clad layer having band gap energy larger than that of said first upper clad layer and carrier concentration higher than that of said impurity diffusion preventing layer;
- forming burying layers of high resistance semiconductor on both sides of said waveguide;
- and
- forming, on at least said waveguide, a semiconductor layer of the second conductivity type having carrier concentration higher than that of said second upper clad layer.
1 more element
Dependencies are inferred from the claim text.