Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
  • H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
  • H10F30/21—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation
  • H10F30/26—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices having three or more potential barriers, e.g. photothyristors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
  • H10D62/82—Heterojunctions
  • H10D62/824—Heterojunctions comprising only Group III-V materials heterojunctions, e.g. GaN/AlGaN heterojunctions
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
  • H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
  • H10F30/21—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation
  • H10F30/22—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices having only one potential barrier, e.g. photodiodes
  • H10F30/225—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices having only one potential barrier, e.g. photodiodes the potential barrier working in avalanche mode, e.g. avalanche photodiodes
  • H10F30/2255—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices having only one potential barrier, e.g. photodiodes the potential barrier working in avalanche mode, e.g. avalanche photodiodes in which the active layers form heterostructures, e.g. SAM structures

Definitions

• the invention relates to photodetectors and particularly to the field of avalanche photodetectors.
• Photodetectors with high quantum efficiencies in the 1.0-1.6 ⁇ m wavelength region are expected to find wide use in low-loss wide-bandwidth optical fiber transmission systems as well as in other applications.
• Avalanche photodetector devices are of interest here because compared with simple junction photodiodes, they allow a considerable increase in the sensitivity of optical receivers.
• the photon-excited carriers in avalanche devices gain sufficient energy to release new electron-hole pairs by ionization and these new carriers provide gain for the photocurrent.
• the noise factor a measure of the degradation of a photodetector as compared to an ideal noiseless amplifier, increases considerably with the average gain.
• the noise factor of the carrier multiplication process depends both on the ratio between the ionization coefficients, i.e. the ionization probability per unit length, for electrons and for holes and on the way the carrier multiplication is initiated.
• a large difference between ionization coefficients is beneficial for low noise, provided the avalanche is initiated by the carrier type, electron or hole, having the higher ionization coefficient.
• the least noise is obtained for a given gain if the smaller ionization coefficient is zero.
• silicon exhibits a very large difference between the ionization coefficients of electrons and holes, especially at low fields, the response of silicon devices to photons does not extend much beyond 1.1 microns, being basically limited by the 1.12 eV bandgap energy of the silicon.
• Germanium avalanche photodiodes appear to be well suited for detection of photons in the wavelength range of 1.1-1.5 microns. However, germanium has almost equal electron and hole ionization coefficients, causing these devices to suffer from the excess noise of a lessthan-ideal carrier multiplication process.
• a low-noise avalanche semiconductor photodetector device comprises a sequence of at least four contiguous layers of semiconductor material of alternating opposed types of conductivity.
• the layers form alternating homojunctions and heterojunctions at the interfaces between adjacent layers, and the bandgap of the layers on either side of the homojunctions decreases in the direction of the propagating signal.
• the layers form heterojunctions at the interfaces between adjacent layers; the layers are grouped into a sequence of pairs of layers where the bandgap of the two layers in each pair are substantially equal, and the bandgap of the layers in the sequence of pairs of layers decreases in the direction of the propagating signal.
• the second layer of at least one pair of the sequence is lightly doped.
• low-noise multistage avalanche photodetector devices may be fabricated from materials comprising III-V semiconductor components, II-VI semiconductor components, group IV elemental semiconductor components or combinations of them all. This enables the devices to be fabricated out of materials whose region of wavelength sensitivity may be continuously varied over the region of the spectrum suitable for optical fiber communications.
• FIG. 1 shows in partially schematic, partially pictorial form an embodiment of the present invention wherein a 2-stage pn-pn structure having two pn homojunctions is formed on an appropriate substrate material and the structure includes means for applying an appropriate bias;
• FIG. 2 shows in pictorial form the electronic band structure for the device shown in FIG. 1 after biasing
• FIG. 4 shows in pictorial form an embodiment of the present invention wherein a 2-stage pn-pn photodetector device is fabricated out of an
• FIG. 5 is a graphical representation of liquidus and solidus data for growth of InP.
• the data show liquid atomic fractions and solid compositions x, y versus for this process.
• the smooth curve drawn through the vs. points is the locus of liquid compositions which provide lattice-matched growth;
• FIG. 7 shows the room temperature bandgap of the quaternary as a function of the liquid atomic fraction
• FIG. 8 shows in pictorial form the electronic band structure for a 2-stage pn-pn device having two pn homojunctions constructed according to the present invention with a lightly doped floating n layer, i.e. a layer having no applied bias voltage
• FIG. 9 shows in pictorial form the electronic band structure for a 2-stage np-np device having two np homojunctions constructed according to the present invention with a lightly doped floating p-layer.
• An avalanche photodetector constructed according to an illustrative embodiment of the present invention comprises a sequence of at least four contiguous layers of semiconductor material of alternating opposed types of conductivity.
• the layers form alternating homojunctions and heterojunctions at the interfaces between adjacent layers and the bandgap of the layers on either side of the homojunctions decreases in the direction of the propagating signal.
• the second layer of at least one pair of layers of the sequence is lightly doped. The effect of the multilayer device is to create traps for one sign of carrier and to prevent the trapped carrier from avalanching through the several amplifier stages.
• FIG. 1 is a schematic diagram of 2-stage electron amplifying device 1 having heterojunction 1.1 between the amplifier stage formed from p layer 10 and n layer 11 and the amplifier stage formed from p layer 12 and n layer 13.
• Heterojunction 1.1 allows the passage of electrons there through but blocks the passage of holes. This suppresses the noise-producing effect of further ionization by holes if they could cause avalanching at homojunction 10.1.
• FIGS. 1 and 2 concerns an electron current amplifying device, a hole current amplifying device is equally feasible when constructed according to the present invention.
• the particular choice as to the carrier current chosen is determined by choosing the carrier having the higher gain coefficient in the specific materials out of which the device is to be fabricated.
• the device shown in FIG. 1 is a sandwich of p material 10, n material 11, p material 12, and n material 13 grown on substrate 3.
• the bandgaps of p material 10 and n material 11 are equal to E g1
• the bandgaps of p material 12 and n material 13 are equal to E g2 .
• the pn junction 10.1 between p material 10 and n material 11 is a homojunction as is pn junction 11.1 between p material 12 and n material 13.
• the np junction 1.1 is a heterojunction and E g1 is larger than
• E g2' i.e.r E g1 > E g2 .
• Photon 20 impinges on substrate 3 through a window in electrode 2 and passes unhindered therethrough, substrate 3 being transparent to photon 20.
• Substrate 3 is typically made transparent to photons by fabricating it from a material whose bandgap energy is larger than the energy of the photons in the photon flux to be detected.
• Photon 20 is absorbed in p layer 10.
• p layer 10 is made thin enough so that photoelectrons generated by the absorption of photon 20 can reach pn junction 10.1 by diffusion.
• heavy line 50 represents the energy level of the bottom of the conduction band and heavy line 51 represents the energy level of the top of the valence band in the various regions 61, 62, 63 and 64 of the device.
• Photon 20 which is incident on region 61, corresponding to p material 10 in FIG. 1, generates electron-hole pair 20.1 and 20.2.
• Electron 20.1 diffuses through region 61 toward pn homojunction 10.1.
• Electron 20.1 is accelerated by the electric field at junction 10.1 and produces new electron-hole pairs which themselves have the possibility of further production of pairs.
• the result of the mechanism is that for each photon absorbed M 1 electrons enter region 62, corresponding to n material 11 in FIG.
• region 63 Due to the energy level configuration of region 63 the holes are trapped and cannot travel through regions 62 and 61 to emerge from the device. The trapped holes are removed either by recombination or by allowing them to leak out of electrode 21, which is shown as being affixed to p layer 12 in FIG. 1. The result is that the reentry of the M 1 (M 2 -1) holes into the first avalanche region at pn homojunction 10.1 has been prevented. This provides for the dramatic reduction of noise for the device.
• Curves 302 and 303 are for devices having equal gain per stage and curves 304 and 305 are for devices having gain ratios which were optimized as per the discussion hereinabove.
• the devices which may be fabricated according to the principles of the present invention are not restricted to these choices.
• the devices may also be made from materials chosen from compounds comprising elements from Groups II and VI of the Periodic Table of the Elements.
• the particular choice of materials depends on the region of the electromagnetic spectrum which is to be detected. Examples of lattice-matched systems such as InGaAs/Ge, GaAsSb/Ge, CdTe/InGaSb and CdTe/InSbAs utilize column IV elemental homojunctions or II-VI compound homojunctions along with III-V compound junctions in each device.
• Patent 3,928,261 teaches how to grow an epitaxial layer of a quaternary III-V compound of Ga,In,As,P with its constants proportioned for lattice-matching to a substrate comprising a binary III-V compound of the elements In and P where the constants of the alloy are proportioned to provide a selected bandgap energy.
• the patent discloses growth of the quaternary compound on InP(lll) substrates.
• the growth is carried out in a quartz reaction tube under a Pd-purified H 2 hydrogen ambient, using a split, horizontal furnace.
• a multi-well graphite boat and slider arrangement is used to hold the growth solutions and to transport the InP substrate.
• the solutions consist of accurately weighed 99.9999 percent pure In and undoped polycrystalline GaAs and InAs, along with excess single crystal ⁇ 100> InP.
• the liquid-encapsulated-Czochralski grown InP substrates, 0.75 x 1.0 cm 2 in area, are ⁇ 100> oriented to within ⁇ 0.5° or better.
• Substrate preparation includes mechanical lapping followed by chemical-mechanical polishing in 10 percent (volume) Br:methanol to a final thickness ⁇ 0.25 mm.
• the bandgap of the quaternary formed is shown as a function of the liquid atomic fraction of Ga.
• the curves in FIG. 5 represent the liquidus and solidus data for the growth process.
• the smooth curves drawn through the points, where are the liquid atomic fractions of As and Ga respectively, are the loci of liquid compositions giving lattice-matched growth by this method.
• FIG. 6 shows the Ga and As distribution coefficients, as functions of y.
• the curve in FIG. 7, together with the curves of FIG. 5 enables one to design the liquid solution necessary to grow any lattice matched In 1 _ ⁇ Ga ⁇ As y P 1-y composition at any wavelength in the range 0.92 ⁇ ⁇ ⁇ 1.65 ⁇ m.
• Electrical contacts may be made to n and p layers by electroplating with Sn-Ni-Au and Au respectively.
• the substrates of the devices grown according to the first aspect of the present invention may serve as a window layer for the incident radiation as in FIG. 1.
• use of an InP substrate causes the short wavelength limit of the device to be near 0.9 ⁇ m due to the absorption edge in the InP, i.e., radiation having ⁇ ⁇ 0.95 ⁇ m is absorbed in thick substrate windows.
• the InP window layer may be replaced by a lattice-matched In 1 _ ⁇ Ga ⁇ As y P 1-y layer in order that the short wavelength response limit of these devices may be compositionally tuned in the same manner as the long wavelength response.
• FIG. 8 shows the energy level structure of a 2-stage pn-pn device constructed according to the first aspect of the present invention shown in FIG. 1 where floating n layer 11 in FIG. 1, i.e., that layer having no applied bias voltage, is doped so lightly that it is fully depleted under normal operating conditions. This means that all residual background electrons are swept out of region 62 in FIG. 8 by the applied voltage and the electric field region of homojunction 10.1 extends throughout region 62.
• This device should have a faster response time than devices fabricated with an undepleted floating n-layer.
• the reason for this is because the response time of devices having an undepleted floating n-layer is affected by the manner in which the forward biased np heterojunction, junction 1.1 in FIG. 1, alters its electron-hole energy levels in the presence of injected electrons.
• np heterojunction 1.1 does not allow residual electrons to flow out of n layer 11 in FIG. 1 until it has been able to adjust itself to allow injected electrons to flow across np heterojunction 1.1 to prevent n-layer 11 from charging. In the device having a fully depleted n-layer 11 no such self-adjustment of np heterojunction 1.1 is required.
• FIG. 9 shows the energy level structure of a 2-stage np-np device constructed according to the first aspect of the present invention where region 131 corresponds to a floating p layer which is doped so lightly that it is fully depleted under normal operating conditions.
• the method of operation of this device is a mirror of the method of operation of a 2-stage pn-pn which has been described hereinabove. Note how region 132 becomes an electron trap for this device and is analogous, to the hole trap formed for the pn-pn device shown as region 63 in FIG. 8.
• An avalanche photodetector constructed according to the present invention comprises a sequence of at least four contiguous layers of semiconductor material of alternating opposed types of conductivity.
• the layers form heterojunctions at the interfaces between adjacent pairs of layers; the layers are grouped into a sequence of pairs of layers where the bandgap of the two layers in each pair are substantially equal; and the size of the bandgap of the layers in the sequence of pairs of layers decreases in the direction of the propagating signal.
• the effect of the multilayer device is to create traps for one sign of carrier and to prevent the trapped carrier from avalanching through the several amplifier stages.
• devices constructed according to the second aspect of the present invention is similar to that for devices constructed according to the first aspect of the present invention.
• the description presented hereinabove for the devices constructed according to the first aspect will allow a person skilled in the art to understand the operation of and the method of constructing devices constructed according to the second aspect of the invention.
• pn homojunctions with equal bandgaps can be made by growing successive layers of a given material which can be doped first p-type and then n-type.
• dissimilar materials of substantially equal bandgaps and lattice constants can provide pn heterojunctions.
• Examples of material systems with these properties are Al 1-u Ga u As/In 1-x Ga ⁇ ASyP 1-y , Al 1 _ u Ga u As v Sb 1 _ v /In 1 _ ⁇ Ga ⁇ As y P 1 _ y , and InP/Al 1-z (In 1-y GayAs) z .
• These examples and many others may be generated by persons skilled in the art by consulting such source material as paper 6 entitled, "III-V Quaternary Alloys" by G. A. Antypas, R. L. Moon, L. W. James, J. Edgecumbe and R. L. Bell,pp. 48-54 in Gallium Arsenide and Related Compounds - Proceedings of the Fourth International Symposium organized by the University of Colorado and sponsored by The British Institute of Physics and Avionic Laboratory of the United States Air Force held at Boulder, Colorado,

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• 1978
  • 1978-10-06 US US05/949,057 patent/US4203124A/en not_active Expired - Lifetime
• 1979
  • 1979-09-13 CA CA000335545A patent/CA1135823A/en not_active Expired
  • 1979-09-21 GB GB8016844A patent/GB2043346B/en not_active Expired
  • 1979-09-21 WO PCT/US1979/000749 patent/WO1980000765A1/en not_active Ceased
  • 1979-09-21 JP JP50163979A patent/JPS55500788A/ja active Pending
  • 1979-09-21 NL NL7920079A patent/NL7920079A/nl not_active Application Discontinuation
  • 1979-10-04 BE BE0/197469A patent/BE879196A/fr not_active IP Right Cessation
  • 1979-10-04 AU AU51478/79A patent/AU522867B2/en not_active Ceased
  • 1979-10-05 FR FR7924886A patent/FR2438343A1/fr active Granted
  • 1979-10-05 ES ES484787A patent/ES484787A1/es not_active Expired
  • 1979-10-05 IT IT7968943A patent/IT7968943A0/it unknown
• 1980
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