Abstract: A new reach-through APD structure which includes a five-layer, double-drift-region, double-junction device, having a p.sup.+ -p-n-p.sup.- -n.sup.+ structure. The middle three layers of the new APD constitute most of the thickness of the device and are fully depleted when the device is biased to its normal operating voltage. In the present invention, only primary carriers generated in the relatively narrow first drift region are subject to the full avalanche gain, resulting in dark current and noise levels much lower than conventional reach-through APD's. The new structure can be used to fabricate integrated arrays of APD's. These arrays are more durable and easily fabricated than are prior art APD's. Additionally, the new array structure does not require segmentation or isolation of the multiplying regions of the different elements of the array, allowing arrays to be made with little or no dead space between elements.

Abstract: The invention relates to an avalanche photodetector having a charge-multiplication region which is spatially separated from the detector surface. This photodetector includes a light-absorptive region, an active region overlying the absorptive region forming a heterojunction therebetween. The photodetector includes a central zone which has a greater concentration of conductivity modifiers than the remainder of the active region and is located in the active region extending into the absorptive region. A cap region overlies the active region and has the opposite conductivity type. The cap region extends a greater distance in the lateral direction than the central zone. A photodetector having a central zone extending across the heterojunction between the active region and light absorptive region have exhibited response times comparable with those of photodetectors having a quaternary layer located between the active region and the absorptive region.

Abstract: A semiconductor photodiode includes a substrate of semi-insulating indium phosphide having a first layer of highly doped P type indium phosphide on a surface thereof. An active second layer of N type indium gallium arsenide is on the first layer and a third layer of N type indium gallium arsenide or indium phosphide is on the second layer. The third layer may be entirely more highly doped than the second layer or may have a highly doped region on its surface. A first contact is on the third layer and a second contact is on the first layer. A buffer layer of lightly doped N or P type indium phosphide may be provided between the first layer and the second layer.

Abstract: A photodetector array having reflector means positioned over the low response regions between elements of the array. Light incident on the reflector means is reflected into a high response region of the array. The invention also includes a method of forming the reflector means comprising the steps of forming wedge-shaped projections on the surface of a mold, coating the projections with a reflective material, filling the space between the coated projections with a transparent material and separating the mold from the material with the reflective layer adhered to the material.

Abstract: The invention relates to an avalanche photodetector having a charge-multiplication region which is spatially separated from the detector surface. This photodetector includes a light-absorptive region, an active region overlying the absorptive region and having a central zone which has a greater concentration of conductivity modifiers than the remainder of the active region. A cap region overlies the first region, has the opposite conductivity type and extends a greater distance in the lateral direction than the central zone. The invention is also a method of forming this detector comprising the steps of forming a first region of the active region, embedding an excess concentration of conductivity modifiers into a portion thereof and then forming a second region of the active region on the first region. A cap region of opposite conductivity type is then formed over the active region. The cap region has a greater lateral extent than the portion containing the excess concentration of conductivity modifiers.

Abstract: The invention is an improved avalanche photodiode having reduced electrical noise arising from spurious surface generation of charge carriers. The avalanche photodiode includes active and neighboring regions adjacent a first surface of a semiconductor body with a gap region therebetween and a channel extending a distance into the semiconductor body from a portion of the second opposed surface opposite the gap region. A P-N junction is formed between regions of opposite conductivity type including a portion thereof over the channel. Since the dopant concentration at the junction is less over the channel, the local avalanche gain over the channel is less, thereby reducing the noise contribution from carriers generated in the gap region.

Abstract: The invention relates to an avalanche photodetector having a charge-multiplication region which is spatially separated from the detector surfaces. This photodetector includes an absorptive region, a first region overlying the absorptive region, a second region overlying the first region and having a central zone which is thinner than a peripheral zone and a third region overlying the second region. The high electric field required for avalanche multiplication is then restricted to the portion of the first region adjacent the central zone while the field at the periphery is less than that necessary for avalanche multiplication.

Abstract: The invention relates to an avalanche photodetector having a charge-multiplication region which is spatially separated from the detector surfaces. This photodetector includes an absorptive region, a first region overlying the absorptive region and having a higher concentration zone and a surrounding peripheral zone and a second region overlying the first region. The high electric field in the avalanche region is then restricted to the higher conductivity central zone thereby reducing the electric field at the detector surfaces when a reverse-bias voltage sufficient to produce avalanche multiplication is applied to the detector.

Abstract: The invention relates to a photodetector wherein the avalanche region is separated from the detector surfaces by a region in which the electric field under reverse bias will be less than in the avalanche region. This photodetector includes an absorptive region having a planar surface area surrounded by a non-planar surface area. A first region overlies the planar area and a second region of opposite conductivity type overlies both the first region and the non-planar area of the absorptive region. The high electric fields are restricted to the first region which is isolated from the surfaces of the photodetector.

Abstract: A p-.nu.-n Si photodiode having an n-type control layer extended into the silicon body from a portion of the surface contiguous to that portion from which a p-type region extends. Photodiodes incorporating this control layer have a much higher junction resistance.The invention also includes an improved method of making a photodiode which has a reduced number of processing steps. The improvement comprises implanting As or Sb into the surface of a .nu.-type Si body to form an n-type layer prior to the steps of passivating the surface and forming a p-type region extending into the body from the surface.

Abstract: An n-p-.pi.-p.sup.+ Si avalanche photodiode wherein the number of acceptors introduced into a Si body to form the p-type conductivity region has been reduced and this region extends a distance greater than about 35 micrometers into the body from the surface and wherein the n-type conductivity region extends a distance into the body such that the p-n junction is less than about 10 micrometers from the surface of the body. The method of the invention comprises introducing a reduced number of acceptors into the surface of the body, diffusing the acceptors into the body a distance greater than about 35 micrometers and forming an n-type conductivity region such that the p-n junction is less than 10 micrometers from the surface of the device. APDs of the invention exhibit a k.sub.eff of about 0.006 which is a factor of greater than 2.5 less than that of typical prior art devices.

Abstract: The invention is an APD array having a plurality of p-n junctions. The p-n junctions comprise a plurality of separate regions which extend a distance into a semiconductor body from a surface thereof and have a conductivity type opposed to that of the body. A region of the same conductivity type as that of the body extends a further distance into the body and is composed of sub-regions which overlap one another in the direction parallel to the surface of the body. The elements so formed have a more uniform avalanche gain and, because of the overlap of the sub-regions of first conductivity type, the likelihood of electric breakdown at the surface is reduced and the electrical isolation between the elements is increased. Moreover, because of the proximity of the adjacent elements the likelihood of breakdown at the junction edges is reduced.

Abstract: The invention is an improved avalanche photodiode having higher sensitivity at short wavelengths and a method of making it. The improvement comprises a contacting layer of varying thickness which can have a thin portion through which light enters the avalanche photodiode and a thicker portion surrounding the thin portion to which electrical contact can be made. This structure exhibits substantially greater sensitivity at wavelengths less than 500 nanometers without affecting the long wavelength sensitivity. The invention is also a method of forming the avalanche photodiode where the thicker portion and the thinner portions are sequentially formed using a two-step diffusion process.

Abstract: The light entry surface or back surface of an avalanche or p-i-n photodiode is contoured in a regular array of indentations which are hemispherical or almost hemispherical in shape. Light incident on the photodiode undergoes multiple interactions with the contoured surface, thus reducing the entry surface reflectivity and increasing the optical path length in the photodiode, and thereby enhancing its long wavelength response.

Abstract: A light pipe is inserted through the cap of a light detector housing and bonded to this cap. Light from a light transmitting fiber which impinges on the external end of the light pipe is transmitted with reduced loss of light to the light detector inside the housing.

Abstract: Avalanche photodiodes include a substrate of a high resistivity material having at least a first surface. The substrate is of a particular conductivity type. In the substrate and at the first surface are a plurality of spaced apart regions of the same conductivity type as the substrate and defining the individual photodiode elements of the avalanche photodiode. Occupying the area at the first surface of the substrate not occupied by the spaced regions and extending into the substrate is a discontinuous layer of the same conductivity type as the spaced regions but of a conductivity concentration much lower than the conductivity concentration of the spaced regions. On the first surface of the substrate covering the discontinuous layer and slightly overlapping the spaced regions is a patterned passivation layer. The improvement of the present invention over the prior art is the addition of the discontinuous layer which reduces the electrical noise in the output signal of the avalanche photodiode.