Heterojunction photodiode of the avalanche type
AssigneeThomson-CSF
InventorThomas Pearsall
Life of this patent
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Abstract
A photodiode comprising a first layer of a relatively large forbidden band (e.g. 1.4 eV) in a p type of conductivity, wherein photons can be absorbed, thus creating pairs of electron-holes diffusing towards a second layer, said second layer having a forbidden band. (0.7 eV) that is approximately half of the first band. In that second layer of an n-type of conductivity each electron falls and creates by impact ionization a new pair electron-hole, thus producing an avalanche gain of 2. The phenomenon occurs theoretically with a zero bias voltage. In practice the photodiode operates with a bias voltage near zero. The two materials of the heterojunction are for instance In P (forbidden band: 1.4 eV) and Ga.sub.0.47 In .sub.0.53 As (0.7 eV) providing crystalline networks perfectly matched.
Claims3
An avalanche photodiode of the type provided with a semiconductor junction consisting of two different materials having opposite types of conductivity, comprising:
- a first semiconductor layer of an alloy having the formula In P, intended to absorb photons the energy of which is greater than or equal to E.sub.1, the material constituting said first layer exhibiting a forbidden band gap having a width of E.sub.2, expressed in energy;
- a second semiconductor layer adjacent to the first layer, and formed of an alloy having the formula
- Ga.sub.x In.sub.1-x As
- wherein x=0.47 within a few thousandths, said second layer exhibiting a forbidden band gap having a width of E.sub.3, expressed in energy;
- a monocrystalline substrate having the formula In P;
- said semiconductor junction being formed by said first layer having a first type of conductivity, which is strongly doped, and said second layer having an opposite type of conductivity, less doped than the first layer, the energies E.sub.1, E.sub.2 and E.sub.3 complying with the following double relationship:
- E.sub.1 >E.sub.2 .gtoreq.2E.sub.3.
An avalanche photodiode of the type provided with a semiconductor junction consisting of two different materials having opposite types of conductivity, comprising:
- a first semiconductor layer of an alloy having the formula Ga Sb, intended to absorb photons the energy of which is greater than or equal to E.sub.1, the material constituting said first layer exhibiting a forbidden band gap having a width of E.sub.2, expressed in energy;
- a second semiconductor layer adjacent to the first layer, and formed of an alloy having the formula
- Al.sub.y Ga.sub.1-y Sb
- wherein y=0.61 within a few thousandths, said second layer exhibiting a forbidden band gap having a width of E.sub.3, expressed in energy;
- a monocrystalline substrate having the formula Ga Sb;
- said semiconductor junction being formed by said first layer having a first type of conductivity, which is strongly doped, and said second layer having an opposite type of conductivity, less doped than the first layer, the energies E.sub.1, E.sub.2 and E.sub.3 complying with the following double relationship:
- E.sub.1 >E.sub.2 .gtoreq.2E.sub.3.
An avalanche photodiode of the type provided with a semiconductor junction consisting of two different materials having opposite types of conductivity, comprising:
- a first semiconductor layer intended to absorb photons having an energy greater than or equal to E.sub.1, the material constituting said first layer exhibiting a forbidden band gap having a width of E.sub.2 (expressed in energy);
- a second semiconductor layer adjacent to the first layer and intended to serve as an avalanche zone;
- said second layer exhibiting a forbidden band gap having a width of E.sub.3 (expressed in energy) and complying with the following double relationship,
- E.sub.1 >E.sub.2 .gtoreq.2E.sub.3 ;
- said avalanche photodiode comprising a first p (or n) doped layer with a density in acceptor (or donor) atoms of 2.10.sup.18 cm.sup.-3, a second n (or p) doped layer with a density in donor (or acceptor) atoms of the order of 10.sup.16 cm.sup.-3, a third layer, serving as a buffer, of an alloy identical with that of which the substrate consists, n (or p) doped and with a density in donor (or acceptor) atoms of the order of 10.sup.18 cm.sup.-3, and an n (or p) doped substrate with a density in donor (or acceptor) atoms of the order of 2.10.sup.18 cm.sup.-3.
Dependencies are inferred from the claim text.