Semiconductor photodetector with dielectric shielding

A semiconductor photodetector comprising:

• a photodiode chip having an n.sup.+ -type InP substrate, an undoped InP buffer layer deposited on the n.sup.+ -type InP substrate, an undoped InGaAs receiving layer deposited on the undoped InP buffer layer, an undoped InP window layer, a p-type region selectively formed on a central part of the undoped InP window layer and upper part of the InGaAs receiving layer, the p-type region being a photosensitive area, an electrode formed on the p-type region, another electrode formed on the InP substrate, an antireflection film deposited on the p-type region which is the photosensitive area, a passivation film deposited on the undoped InP window layer, and a dielectric layer formed on the passivation film for preventing light beams from reaching the undoped InGaAs receiving layer by reflecting or absorbing the light beams,
• a header on which the photodiode chip is mounted,
• a cylindrical receptacle welded to the header,
• leads piercing the header and being connected to the electrodes of the photodiode chip for sending current, and
• a ferrule holding an end of an optical fiber for transmitting light signals, the ferrule being inserted and fixed in the receptacle,
• wherein light beams emitted from the optical fiber directly reach the photodiode chip without passing through a lens and a dielectric layer is formed outside the photosensitive area on the photodiode chip for preventing light beams from reaching the undoped InGaAs receiving layer by reflecting or absorbing the light beams.