WO2005011003A1 - Photodetector and method for the production thereof - Google Patents

Photodetector and method for the production thereof Download PDF

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Publication number
WO2005011003A1
WO2005011003A1 PCT/DE2004/001295 DE2004001295W WO2005011003A1 WO 2005011003 A1 WO2005011003 A1 WO 2005011003A1 DE 2004001295 W DE2004001295 W DE 2004001295W WO 2005011003 A1 WO2005011003 A1 WO 2005011003A1
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Prior art keywords
absorption layer
electrodes
photodetector
ohmic contacts
resistance
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PCT/DE2004/001295
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German (de)
French (fr)
Inventor
Martin Mikulics
Michel Marso
Peter Kordos
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Forschungszentrum Jülich GmbH
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Priority to DE112004001156T priority Critical patent/DE112004001156B4/en
Publication of WO2005011003A1 publication Critical patent/WO2005011003A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier
    • H01L31/108—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier the potential barrier being of the Schottky type
    • H01L31/1085—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier the potential barrier being of the Schottky type the devices being of the Metal-Semiconductor-Metal [MSM] Schottky barrier type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/09—Devices sensitive to infrared, visible or ultraviolet radiation

Definitions

  • the invention relates to a photodetector and a method for its production.
  • Photodetectors are used to convert light signals into electrical signals and z. B. used in optical communication.
  • a photodetector known from the prior art consists of two metal contacts on the surface of a semiconductor. With this so-called MSM photodetector (MSM: Metal-Semiconductor-Metal), the
  • Electrodes z. B. be designed as Schottky contacts. Then the component works as a photodiode with two anti-serial Schottky diodes. However, if the electrodes are designed as ohmic contacts, a photoresistor is obtained.
  • MSM photodetectors are manufactured according to the state of the art on all common semiconductor materials, e.g. B. on Si, GaAs, InP, GaN, both with Schottky contacts and as photoresistors.
  • Materials with a high density of recombination centers are particularly suitable for the production of ultrafast photoresistors, which greatly reduce the lifespan of the photogenerated charge carriers.
  • One example is the so-called low temperature grown GaAs (LT-GaAs), which is produced at low temperatures of eg 200 ° C for epitaxial conditions.
  • Ion implantation is also used to isolate electrical components by greatly reducing the conductivity in the areas between the components.
  • a further disadvantage is that the field peaks generated by the inhomogeneous field distribution lead to a reduced dielectric strength of the detector.
  • the MSM photodetector is designed as a photoresistor, the requirement for a high electrical resistance of the semiconductor in order to achieve the lowest possible dark current contradicts Desire for a low contact resistance of the electrodes, which requires the lowest possible resistance of the semiconductor material.
  • the object of the invention is to provide a photodetector with a high electrical resistance of the semiconductor to achieve the lowest possible dark current, which has a low contact resistance of the electrodes with the lowest possible resistance of the semiconductor material.
  • the photodetector comprises an absorption layer and at least two electrodes designed as ohmic contacts on and / or in the absorption layer.
  • the specific resistance of the absorption layer in the area between the electrodes is greater than one in relation to the specific resistance of the absorption layer in the immediate area at the electrodes.
  • the ratio is advantageously at least 10.
  • the specific resistance between the electrodes can be, for example, in the megohm or gigaohm range, the resistance in the immediate range of the electrodes in the ohm or kiloohm range.
  • the absorption layer has between the electrodes thus a comparatively high resistance.
  • the absorption layer has a lower resistance.
  • the specific resistance of the absorption layer between the electrodes or in the immediate area at the electrodes is set in such a way that a homogeneous electric field is present between the electrodes.
  • a high resistance of the absorption layer in the area between the contacts creates a homogeneous electric field there, which is aligned essentially parallel to the surface when an electrical voltage is present between the contacts. This suppresses the reduction in the speed of the detector by generating charge carriers in low-field areas and avoids field peaks that lead to breakdown even at low applied voltages.
  • the electrodes in the absorption layer, provided that a lower resistance than in the area between the electrodes can then be set towards the surface of the absorption layer or towards the substrate.
  • the two electrodes are usually n- or p-doped for better contactability
  • Semiconductor layer arranged as an absorption layer.
  • the area between the contacts is provided with so many impurities that the ohmic resistance is greatly increased and photogenerated charge carriers quickly recombine.
  • the absorption layer below the contact is highly conductive.
  • absorption layer and electrodes is advantageously arranged on an insulating or semi-insulating substrate as a base layer.
  • Such photodetectors thus represent semiconductor-based components for converting light into electrical current.
  • the light penetrates into the component from above, essentially perpendicular to the substrate surface.
  • the process for producing the photodetector comprises the steps:
  • the absorption layer can be modified by implantation or by diffusion with suitable ions.
  • the ion implantation is then carried out with a dose and energy which is sufficient to increase the resistance of the absorption layer in the region between the electrodes from its surface to the substrate.
  • the material of the absorption layer between the electrodes is changed so that the speed of the photodetector is increased overall by the creation of recombination centers and the service life of the photo-generated charge carriers is reduced.
  • the ion implantation is carried out with suitable elements, such as. B. nitrogen or silicon, which greatly increase the ohmic resistance between the electrodes, so that photogenerated charge carriers recombine faster.
  • the contacting of the photodetector takes place, for. B. by means of insulation layers, contact pads and so on.
  • a photodetector has the known advantages of the MSM components. It is a pla- nares component, which means that no etching is required, which saves work steps and simplifies subsequent production steps, in particular the lithography.
  • the conductivity of the semiconductor material below the ohmic contacts can be chosen regardless of the dark current of the photodetector.
  • the ion implantation procedure is self-adjusting only in the areas outside the ohmic contacts, because the contact material itself acts as an implantation mask. This saves expensive lithographic processing steps and allows smaller dimensions between the electrodes because no adjustment tolerances have to be planned.
  • Figure 1 shows a photodetector according to the prior art.
  • Figure 2 shows a photodetector according to the invention.
  • FIG. 3 shows a method according to the invention for producing the photodetector.
  • FIG. 1 when an electrical voltage is applied between the electrodes 1, an electrical field 3 is generated in the semiconductor.
  • This field 3 moves photogenerated charge carriers and thus generates a photocurrent.
  • the electric field is disadvantageously inhomogeneous, that is to say it becomes weaker with increasing depth in the semiconductor, as shown in FIG. 1 in relation to the prior art. Because the speed of the photogenerated charge carriers depends on the electric field strength, the photogenerated charge carriers in the depth disadvantageously increase the response time of the detector.
  • a further disadvantage is that the field peaks generated by the inhomogeneous field distribution lead to a reduced dielectric strength of the detector.
  • FIG. 2 shows an MSM photoresistor based on GaAs according to the invention with a wavelength to be detected of less than 910 nanometers.
  • the substrate 24 is made of semi-insulating GaAs.
  • the absorption layer 22 consists of GaAs and has a thickness of, for example, 0.1 to 10 micrometers. In the present example, photons with a wavelength of 850 nanometers penetrate GaAs up to 1 micron deep into the absorption layer 22.
  • the absorption layer 22 is thus of the n-type.
  • the electrodes 21 comprise a metallic layer sequence made of Ni / AuGe / Ni with respective thicknesses of 5, 90 and 25 nanometers. If necessary, the electrodes can be reinforced with an additional metal layer (e.g. gold) with a thickness of 50 to 500 nanometers for better shielding during ion implantation.
  • the electrodes 21 have a length of 100 nanometers to 20 micrometers and a distance of 100 nanometers to 20 micrometers.
  • FIG. 2 shows a 2-finger layout with respect to the electrodes 21. However, an interdigital multifinger layout can also be implemented.
  • the first step is to produce a conductive absorption layer 32 on an insulating or semi-insulating semiconductor material as substrate 34, e.g. B. by epitaxy or by ion implantation.
  • electrodes 31 are produced as ohmic contacts on the conductive layer 32, e.g. B. by applying suitable metal layers and alloying ( Figure 3b).
  • the implantation process which is indicated by arrows in FIG. 3c, runs in a self-adjusting manner only in the areas between the contacts 31. If necessary, the ohmic contacts 31 can be strengthened by applying suitable materials.
  • the ion implantation is carried out with N, Ar, 0, H, He, Si or another suitable element.
  • the acceleration voltage is, for example, 10 kV to 10 MV.
  • the dose is, for example, 10 12 to 10 18 cm “2 .
  • the high-resistance absorption layer is first generated by epitaxy or by ion implantation on a suitable substrate.
  • the low-resistance areas below the ohmic contacts still to be produced are then produced by means of ion implantation.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Light Receiving Elements (AREA)

Abstract

The invention relates to a photodetector. Said photodetector comprises an absorption layer (22) and two electrodes (21) which are designed as ohmic contacts, whereby the absorption layer (22) and the electrodes (21) are arranged on an insulating or semi-insulating substrate (24). For reduction in the dark current of the photodetector, the part of the absorption layer (22a) which is located between the electrodes (21) has a high resistance. However, the part of the absorption layer (22b) below the electrodes (21) has a low resistance. The above results, advantageously, in a reduced contact resistance and in a uniform electric field. A method for producing said photodetector is also provided.

Description

B e s c h r e i b u n g Photodetektor und Verfahren zu seiner Herstellung Description of the photodetector and method for its production
Die Erfindung betrifft einen Photodetektor und ein Verfahren zu seiner Herstellung.The invention relates to a photodetector and a method for its production.
Photodetektoren werden zur Umsetzung von Lichtsignalen in elektrische Signale benutzt und z. B. in der optischen Nachrichtenübertragung eingesetzt.Photodetectors are used to convert light signals into electrical signals and z. B. used in optical communication.
Ein aus dem Stand der Technik bekannter Photodetektor besteht aus zwei Metallkontakten auf der Oberfläche eines Halbleiters. Bei diesem sogenanntem MSM-Photode- tektor (MSM: Metal-Semiconductor-Metal) können dieA photodetector known from the prior art consists of two metal contacts on the surface of a semiconductor. With this so-called MSM photodetector (MSM: Metal-Semiconductor-Metal), the
Elektroden z. B. als Schottky-Kontakte ausgelegt werden. Dann funktioniert das Bauelement als Photodiode mit zwei antiseriell geschalteten Schottkydioden. Werden die Elektroden hingegen als ohmsche Kontakte ausge- legt, dann erhält man einen Photowiderstand.Electrodes z. B. be designed as Schottky contacts. Then the component works as a photodiode with two anti-serial Schottky diodes. However, if the electrodes are designed as ohmic contacts, a photoresistor is obtained.
MSM-Photodetektoren werden gemäß Stand der Technik auf allen gängigen Halbleitermaterialien hergestellt, z. B. auf Si, GaAs, InP, GaN, sowohl mit Schottky-Kontakten als auch als Photowiderstände.MSM photodetectors are manufactured according to the state of the art on all common semiconductor materials, e.g. B. on Si, GaAs, InP, GaN, both with Schottky contacts and as photoresistors.
Zur Herstellung von ultraschnellen Photowiderständen eignen sich insbesondere Materialien mit einer hohen Dichte an Rekombinationszentren, welche die Lebensdauer der photogenerierten Ladungsträger stark herabsetzen. Ein Beispiel ist das sogenannte low temperature grown GaAs (LT-GaAs) , welches bei für Epitaxiebedingungen niedrige Temperaturen von z.B. 200 °C hergestellt wird.Materials with a high density of recombination centers are particularly suitable for the production of ultrafast photoresistors, which greatly reduce the lifespan of the photogenerated charge carriers. One example is the so-called low temperature grown GaAs (LT-GaAs), which is produced at low temperatures of eg 200 ° C for epitaxial conditions.
In Frage kommen auch Halbleiter, bei denen durch Implantation mit geeigneten Ionen tiefe Störstellen er- zeugt werden. Die Ionenimplantation wird auch benutzt zur Isolierung elektrischer Bauelemente durch eine starke Verminderung der Leitfähigkeit in den Bereichen zwischen den Bauelementen.Semiconductors are also suitable, in which deep impurities are created by implantation with suitable ions. Ion implantation is also used to isolate electrical components by greatly reducing the conductivity in the areas between the components.
In beiden Ausführungen, das heißt sowohl bei der Aus- führung der Elektroden als Schottky-Kontakte, als auch bei deren Ausführung als ohmsche Kontakte, wird beim Anlegen einer elektrischen Spannung zwischen den Elektroden ein elektrisches Feld im Halbleiter erzeugt. Dieses Feld bewegt photogenerierte Ladungsträger und er- zeugt so einen Photostrom. Das elektrische Feld ist inhomogen, das heißt es wird mit zunehmender Tiefe im Halbleiter schwächer, wie in Fig. 1 zum Stand der Technik dargestellt. Weil die Geschwindigkeit der photogenerierten Ladungsträger von der elektrischen Feldstärke abhängt, erhöhen die in der Tiefe photogenerierten Ladungsträger nachteilig die Antwortzeit des Detektors.In both versions, that is to say both when the electrodes are in the form of Schottky contacts and when they are in the form of ohmic contacts, an electrical field is generated in the semiconductor when an electrical voltage is applied between the electrodes. This field moves photogenerated charge carriers and thus generates a photocurrent. The electric field is inhomogeneous, that is to say it becomes weaker with increasing depth in the semiconductor, as shown in FIG. 1 in relation to the prior art. Because the speed of the photogenerated charge carriers depends on the electric field strength, the photogenerated charge carriers in the depth disadvantageously increase the response time of the detector.
Weiterhin nachteilig führen die, durch die inhomogene Feldverteilung erzeugten, Feldspitzen zu einer verminderten Spannungsfestigkeit des Detektors.A further disadvantage is that the field peaks generated by the inhomogeneous field distribution lead to a reduced dielectric strength of the detector.
Bei der Ausführung des MSM-Photodetektors als Photowiderstand, steht die Forderung nach einem hohen elektrischen Widerstand des Halbleiters zur Erzielung eines möglichst niedrigen Dunkelstromes im Widerspruch zum Wunsch nach einem niedrigen Kontaktwiderstand der Elektroden, welcher einen möglichst kleinen Widerstand des Halbleitermaterials voraussetzt.When the MSM photodetector is designed as a photoresistor, the requirement for a high electrical resistance of the semiconductor in order to achieve the lowest possible dark current contradicts Desire for a low contact resistance of the electrodes, which requires the lowest possible resistance of the semiconductor material.
Aufgabe der Erfindung ist es einen Photodetektor mit einem hohen elektrischen Widerstand des Halbleiters zur Erzielung eines möglichst niedrigen Dunkelstromes bereit zu stellen, der einen niedrigen Kontaktwiderstand der Elektroden mit möglichst kleinen Widerstand des Halbleitermaterials aufweist.The object of the invention is to provide a photodetector with a high electrical resistance of the semiconductor to achieve the lowest possible dark current, which has a low contact resistance of the electrodes with the lowest possible resistance of the semiconductor material.
Die Aufgabe wird durch einen Photodetektor nach Anspruch 1 und ein Verfahren gemäß Nebenanspruch gelöst . Vorteilhafte Ausgestaltungen ergeben sich aus den darauf rückbezogenen Ansprüchen.The object is achieved by a photodetector according to claim 1 and a method according to the independent claim. Advantageous refinements result from the claims which refer back to them.
Gemäß Hauptanspruch umfasst der Photodetektor eine Ab- sorptionsschicht und mindestens zwei als ohmsche Kontakte ausgeführte Elektroden auf und/oder in der Absorptionsschicht. Der spezifische Widerstand der Absorptionsschicht im Bereich zwischen den Elektroden ist im Verhältnis zum spezifischen Widerstand der Absorpti- onsschicht im unmittelbaren Bereich an den Elektroden größer eins .According to the main claim, the photodetector comprises an absorption layer and at least two electrodes designed as ohmic contacts on and / or in the absorption layer. The specific resistance of the absorption layer in the area between the electrodes is greater than one in relation to the specific resistance of the absorption layer in the immediate area at the electrodes.
Das Verhältnis beträgt vorteilhaft mindestens 10. Der spezifische Widerstand zwischen den Elektroden kann beispielsweise im Megaohm- oder Gigaohm-Bereich, der Widerstand im unmittelbaren Bereich der Elektroden im Ohm oder Kiloohm-Bereich liegen.The ratio is advantageously at least 10. The specific resistance between the electrodes can be, for example, in the megohm or gigaohm range, the resistance in the immediate range of the electrodes in the ohm or kiloohm range.
Zur Erniedrigung des Dunkelstromes des Photodetektors weist die Absorptionsschicht zwischen den Elektroden somit einen vergleichsweise hohen Widerstand auf. Unterhalb, im Falle von Elektroden, die in der -Absorptionsschicht angeordnet sind, im unmittelbaren Bereich an den Elektroden, weist die Absorptionsschicht einen niedrigeren Widerstand auf .To lower the dark current of the photodetector, the absorption layer has between the electrodes thus a comparatively high resistance. Below, in the case of electrodes which are arranged in the absorption layer, in the immediate area on the electrodes, the absorption layer has a lower resistance.
Dadurch wird vorteilhaft bewirkt, dass der Kontaktwiderstand erniedrigt ist .This advantageously has the effect that the contact resistance is reduced.
Der spezifische Widerstand der Absorptionsschicht zwischen den Elektroden bzw. im unmittelbaren Bereich an den Elektroden ist dabei derartig eingestellt, dass zwischen den Elektroden jedenfalls ein homogenes elektrisches Feld vorliegt.The specific resistance of the absorption layer between the electrodes or in the immediate area at the electrodes is set in such a way that a homogeneous electric field is present between the electrodes.
Durch einen hohen Widerstand der Absorptionsschicht im Bereich zwischen den Kontakten entsteht dort ein homo- genes elektrisches Feld, das im wesentlichen parallel zur Oberfläche ausgerichtet ist, wenn eine elektrische Spannung zwischen den Kontakten anliegt . Dadurch wird die Reduzierung der Geschwindigkeit des Detektors durch die Generierung von Ladungsträgern in Niedrigfeldberei- chen unterdrückt, und es werden Feldspitzen vermieden, welche zum Durchbruch schon bei niedrigen angelegten Spannungen führen.A high resistance of the absorption layer in the area between the contacts creates a homogeneous electric field there, which is aligned essentially parallel to the surface when an electrical voltage is present between the contacts. This suppresses the reduction in the speed of the detector by generating charge carriers in low-field areas and avoids field peaks that lead to breakdown even at low applied voltages.
Es ist, wie erwähnt, auch denkbar die Elektroden in der Absorptionsschicht anzuordnen, sofern dann zur Oberflä- ehe der Absorptionsschicht hin bzw. zum Substrat hin ein niedrigerer Widerstand als im Bereich zwischen den Elektroden einstellbar ist.As mentioned, it is also conceivable to arrange the electrodes in the absorption layer, provided that a lower resistance than in the area between the electrodes can then be set towards the surface of the absorption layer or towards the substrate.
Die zwei Elektroden sind zwecks besserer Kontaktierbar- keit aber in der Regel auf einer n- oder p-dotierten Halbleiterschicht als Absorptionsschicht angeordnet. Der Bereich zwischen den Kontakten ist mit so vielen Störstellen versehen, dass der ohmsche Widerstand stark erhöht ist und photogenerierte Ladungsträger schnell rekombinieren. Die AbsorptionsSchicht unterhalb des Kontaktes ist hingegen gut leitend.However, the two electrodes are usually n- or p-doped for better contactability Semiconductor layer arranged as an absorption layer. The area between the contacts is provided with so many impurities that the ohmic resistance is greatly increased and photogenerated charge carriers quickly recombine. The absorption layer below the contact, on the other hand, is highly conductive.
Ein Bereich mit niedriger Feldstärke in der Absorptionszone wird vermieden, welche das Bauelement verlangsamen würde. Die Widerstandserhöhung durch Ionenimplan- tation bewirkt gleichzeitig eine Isolierung des Bauelementes gegenüber anderen Bauelementen auf demselben Substrat und macht somit vorteilhaft eine Mesa-Ätzung überflüssig.An area with low field strength in the absorption zone is avoided, which would slow down the component. The increase in resistance by means of ion implantation simultaneously causes the component to be isolated from other components on the same substrate and thus advantageously makes mesa etching unnecessary.
Die Anordnung aus Absorptionsschicht und Elektroden ist vorteilhaft auf einem isolierenden oder semiisolierenden Substrat als Tragschicht angeordnet.The arrangement of absorption layer and electrodes is advantageously arranged on an insulating or semi-insulating substrate as a base layer.
Derartige Photodetektoren stellen somit Bauelemente auf Halbleiterbasis zur Umwandlung von Licht in elektrischen Strom dar. Das Licht dringt im wesentlichen senk- recht zur Substratoberfläche von oben in das Bauelement ein.Such photodetectors thus represent semiconductor-based components for converting light into electrical current. The light penetrates into the component from above, essentially perpendicular to the substrate surface.
Das Verfahren zur Herstellung des Photodetektors um- fasst die Schritte:The process for producing the photodetector comprises the steps:
Herstellung einer leitenden Absorptionsschicht auf einem isolierenden oder semiisolierenden Halbleitermaterial als Substrat,Production of a conductive absorption layer on an insulating or semi-insulating semiconductor material as substrate,
- Herstellung von mindestens zwei Elektroden als ohmsche Kontakte auf und/oder in der leitenden Absorp- tionsschicht ,- Production of at least two electrodes as ohmic contacts on and / or in the conductive absorber tion layer,
- Modifizierung der Absorptionsschicht zwischen den Elektroden, so dass zwischen den Elektroden ein homogenes elektrisches Feld erzeugt werden kann,Modification of the absorption layer between the electrodes so that a homogeneous electric field can be generated between the electrodes,
- Kontaktierung der Elektroden des Photodetektors.- Contacting the electrodes of the photodetector.
Die Modifizierung der Absorptionsschicht kann mittels Implantation oder Eindiffusion mit geeigneten Ionen erfolgen.The absorption layer can be modified by implantation or by diffusion with suitable ions.
Die Ionenimplantation wird dann mit einer Dosis und Energie ausgeführt die ausreicht, um den Widerstand der Absorptionsschicht im Bereich zwischen den Elektroden von dessen Oberfläche bis zum Substrat zu erhöhen. Das Material der Absorptionsschicht zwischen den Elektroden wird dabei so verändert, dass durch die Erzeugung von RekombinationsZentren die Geschwindigkeit des Photodetektors insgesamt erhöht wird und die Lebensdauer der photogenerierten Ladungsträger verringert wird.The ion implantation is then carried out with a dose and energy which is sufficient to increase the resistance of the absorption layer in the region between the electrodes from its surface to the substrate. The material of the absorption layer between the electrodes is changed so that the speed of the photodetector is increased overall by the creation of recombination centers and the service life of the photo-generated charge carriers is reduced.
Die Ionenimplantation erfolgt mit geeigneten Elementen, wie z. B. Stickstoff oder Silizium, die den ohmschen Widerstand zwischen den Elektroden stark erhöhen, so dass photogenerierte Ladungsträger schneller rekombinieren.The ion implantation is carried out with suitable elements, such as. B. nitrogen or silicon, which greatly increase the ohmic resistance between the electrodes, so that photogenerated charge carriers recombine faster.
Die Kontaktierung des Photodetektors erfolgt z. B. mittels Isolationsschichten, Kontaktpads und so weiter. Ein derartiger Photodetektor besitzt die bekannten Vorteile der MSM-Bauelemente . Es handelt sich um ein pla- nares Bauelement, das heißt es werden keine Ätzungen benötigt, wodurch Arbeitsschritte gespart und nachfolgende Fertigungsschritte, insbesondere die Lithographie vereinfacht werden.The contacting of the photodetector takes place, for. B. by means of insulation layers, contact pads and so on. Such a photodetector has the known advantages of the MSM components. It is a pla- nares component, which means that no etching is required, which saves work steps and simplifies subsequent production steps, in particular the lithography.
Die Leitfähigkeit des Halbleitermaterials unterhalb der ohmschen Kontakte kann dabei ohne Rücksicht auf den Dunkelstrom des Photodetektors gewählt werden.The conductivity of the semiconductor material below the ohmic contacts can be chosen regardless of the dark current of the photodetector.
Das Verfahren mittels Ionenimplantation erfolgt selbstjustierend nur in den Bereichen außerhalb der ohmschen Kontakte, weil das Kontaktmaterial selbst als Implantationsmaske wirkt. Dies erspart kostspielige lithographische Prozessierungsschritte und erlaubt kleinere Abmessungen zwischen den Elektroden, weil keine Justiertoleranzen eingeplant werden müssen.The ion implantation procedure is self-adjusting only in the areas outside the ohmic contacts, because the contact material itself acts as an implantation mask. This saves expensive lithographic processing steps and allows smaller dimensions between the electrodes because no adjustment tolerances have to be planned.
Im weiteren wird die Erfindung an Hand eines Ausführungsbeispiels und der beigefügten Figuren näher beschrieben.The invention is described in more detail below using an exemplary embodiment and the accompanying figures.
Figur 1 zeigt einen Photodetektor gemäß Stand der Technik.Figure 1 shows a photodetector according to the prior art.
Figur 2 zeigt einen erfindungsgemäßen Photodetektor.Figure 2 shows a photodetector according to the invention.
Figur 3 zeigt ein erfindungsgemäßes Verfahren zur Herstellung des Photodetektors.FIG. 3 shows a method according to the invention for producing the photodetector.
In Figur 1 wird beim Anlegen einer elektrischen Spannung zwischen den Elektroden 1 ein elektrisches Feld 3 im Halbleiter erzeugt. Dieses Feld 3 bewegt photogenerierte Ladungsträger und erzeugt so einen Photostrom. Das elektrische Feld ist aber nachteilig inhomogen, das heißt es wird mit zunehmender Tiefe im Halbleiter schwächer, wie in Figur 1 zum Stand der Technik dargestellt . Weil die Geschwindigkeit der photogenerierten Ladungsträger von der elektrischen Feldstärke abhängt, erhöhen die in der Tiefe photogenerierten Ladungsträger nachteilig die Antwortzeit des Detektors. Weiterhin nachteilig führen die, durch die inhomogene Feldverteilung erzeugten, Feldspitzen zu einer verminderten Span- nungsfestigkeit des Detektors.In FIG. 1, when an electrical voltage is applied between the electrodes 1, an electrical field 3 is generated in the semiconductor. This field 3 moves photogenerated charge carriers and thus generates a photocurrent. However, the electric field is disadvantageously inhomogeneous, that is to say it becomes weaker with increasing depth in the semiconductor, as shown in FIG. 1 in relation to the prior art. Because the speed of the photogenerated charge carriers depends on the electric field strength, the photogenerated charge carriers in the depth disadvantageously increase the response time of the detector. A further disadvantage is that the field peaks generated by the inhomogeneous field distribution lead to a reduced dielectric strength of the detector.
In Figur 2 ist ein erfindungsgemäßer MSM-Photowiderstand basierend auf GaAs, mit einer zu detektierenden Wellenlänge von kleiner 910 Nanometern dargestellt.FIG. 2 shows an MSM photoresistor based on GaAs according to the invention with a wavelength to be detected of less than 910 nanometers.
Das Substrat 24 besteht aus semiisolierendem GaAs. Die Absorptionsschicht 22 besteht aus GaAs und weist eine Dicke von beispielsweise 0,1 bis 10 Mikrometer auf. In die Absorptionsschicht 22 dringen im vorliegenden Beispiel Photonen mit 850 Nanometern Wellenlänge in GaAs bis zu 1 Mikrometer tief ein. Die Dotierung der Absorp- tionsschicht erfolgte mit ND = 1016 bis 1019 cm"3 und mit Silizium als Dotierelement. Die Absorptionsschicht 22 ist somit vom n-Typ.The substrate 24 is made of semi-insulating GaAs. The absorption layer 22 consists of GaAs and has a thickness of, for example, 0.1 to 10 micrometers. In the present example, photons with a wavelength of 850 nanometers penetrate GaAs up to 1 micron deep into the absorption layer 22. The absorption layer was doped with N D = 10 16 to 10 19 cm "3 and with silicon as the doping element. The absorption layer 22 is thus of the n-type.
Die Elektroden 21 umfassen eine metallische Schichtenfolge aus Ni/AuGe/Ni mit jeweiligen Dicken von 5, 90 und 25 Nanometern. Bei Bedarf können die Elektroden durch eine zusätzliche Metallschicht (z. B. Gold) mit einer Dicke von 50 bis 500 Nanometern zur besseren Abschirmung bei der Ionenimplantation verstärkt werden. Die Elektroden 21 weisen eine Länge von 100 Nanometern bis 20 Mikrometer und einen Abstand von 100 Nanometer bis 20 Mikrometer auf. Figur 2 zeigt in Bezug auf die Elektroden 21 ein 2-Finger Layout. Es kann aber genauso gut ein interdigitales Multifinger-Layout realisiert werden.The electrodes 21 comprise a metallic layer sequence made of Ni / AuGe / Ni with respective thicknesses of 5, 90 and 25 nanometers. If necessary, the electrodes can be reinforced with an additional metal layer (e.g. gold) with a thickness of 50 to 500 nanometers for better shielding during ion implantation. The electrodes 21 have a length of 100 nanometers to 20 micrometers and a distance of 100 nanometers to 20 micrometers. FIG. 2 shows a 2-finger layout with respect to the electrodes 21. However, an interdigital multifinger layout can also be implemented.
Gemäß der Figur 3a erfolgt zunächst die Herstellung einer leitenden Absorptionsschicht 32 auf einem isolierenden oder semiisolierenden Halbleitermaterial als Substrat 34, z. B. durch Epitaxie oder durch Ionenimplantation.According to FIG. 3a, the first step is to produce a conductive absorption layer 32 on an insulating or semi-insulating semiconductor material as substrate 34, e.g. B. by epitaxy or by ion implantation.
Sodann erfolgt die Herstellung von Elektroden 31 als ohmsche Kontakte auf der leitenden Schicht 32, z. B. durch Aufbringen von geeigneten Metallschichten und Einlegieren (Figur 3b) .Then electrodes 31 are produced as ohmic contacts on the conductive layer 32, e.g. B. by applying suitable metal layers and alloying (Figure 3b).
Der Implantationsprozess, der in Figur 3c durch Pfeile angedeutet ist, verläuft selbstjustierend nur in den Bereichen zwischen den Kontakten 31. Gegebenenfalls können die ohmschen Kontakte 31 durch Aufbringen geeig- neter Materialien verstärkt werden.The implantation process, which is indicated by arrows in FIG. 3c, runs in a self-adjusting manner only in the areas between the contacts 31. If necessary, the ohmic contacts 31 can be strengthened by applying suitable materials.
Die Ionenimplantation erfolgt mit N, Ar, 0, H, He, Si oder einem anderen geeigneten Element. Die Beschleunigungsspannung beträgt beispielsweise 10 kV bis 10 MV. Die Dosis beträgt beispielsweise 1012 bis 1018 cm"2.The ion implantation is carried out with N, Ar, 0, H, He, Si or another suitable element. The acceleration voltage is, for example, 10 kV to 10 MV. The dose is, for example, 10 12 to 10 18 cm "2 .
Zur Verbesserung der Tiefenhomogenität können mehrere Implantationen mit verschiedenen Dosen und Beschleunigungsspannungen vorgenommen werden. Bei einer weiteren vorteilhaften Ausführung wird zuerst die hochohmige Absorptionsschicht durch Epitaxie oder durch Ionenimplantation auf einem geeigneten Substrat erzeugt. Anschließend werden die niederohmigen Bereiche unterhalb der noch herzustellenden ohmschen Kontakte mittels Ionenimplantation hergestellt. To improve depth homogeneity, several implantations with different doses and acceleration voltages can be carried out. In a further advantageous embodiment, the high-resistance absorption layer is first generated by epitaxy or by ion implantation on a suitable substrate. The low-resistance areas below the ohmic contacts still to be produced are then produced by means of ion implantation.

Claims

P a t e n t a n s p r ü c h e Patent claims
1. Photodetektor, umfassend eine Absorptionsschicht (22; 32) und mindestens zwei als ohmsche Kontakte ausgeführte Elektroden (21; 31) auf und/oder in der Absorptionsschicht (22; 32), dadurch gekennzeichnet, dass der spezifische Widerstand der Absorptionsschicht (22a; 32a) im Bereich zwischen den Elektroden (21; 31) im Verhältnis zum spezifischen Widerstand der Absorptionsschicht (22b; 32b) im unmit- telbaren Bereich an den Elektroden größer eins ist.1. photodetector comprising an absorption layer (22; 32) and at least two electrodes (21; 31) designed as ohmic contacts on and / or in the absorption layer (22; 32), characterized in that the specific resistance of the absorption layer (22a; 32a) in the area between the electrodes (21; 31) in relation to the specific resistance of the absorption layer (22b; 32b) in the immediate area at the electrodes is greater than one.
2. Photodetektor, umfassend eine Absorptionsschicht (22; 32) und mindestens zwei als ohmsche Kontakte ausgeführte Elektroden (21; 31) auf und/oder in der Absorptionsschicht (22; 32), dadurch gekennzeichnet, dass der spezifische Widerstand der Absorptionsschicht (22a; 32a) im Bereich zwischen den Elektroden (21; 31) im Verhältnis zum spezifischen Widerstand der Absorptionsschicht (22b; 32b) im unmit- telbaren Bereich an den Elektroden derartig eingestellt ist, dass zwischen den Elektroden ein homogenes elektrisches Feld vorliegt.2. Photodetector comprising an absorption layer (22; 32) and at least two electrodes (21; 31) designed as ohmic contacts on and / or in the absorption layer (22; 32), characterized in that the specific resistance of the absorption layer (22a; 32a) in the area between the electrodes (21; 31) in relation to the specific resistance of the absorption layer (22b; 32b) in the immediate area on the electrodes is set such that a homogeneous electric field is present between the electrodes.
3. Photodetektor nach Anspruch 1 oder 2 , dadurch gekennzeichnet, dass die Absorptionsschicht (22; 32) so dick ist, und/oder bei welchem das Substrat (24; 34) derartig ausgeführt ist, dass das einfallende Licht im we- sentliehen nur Ladungsträger in der Absorptions- schicht (22; 32) erzeugt.3. Photodetector according to claim 1 or 2, characterized in that the absorption layer (22; 32) is so thick, and / or in which the substrate (24; 34) is designed such that the incident light in the- only charge carriers are generated in the absorption layer (22; 32).
4. Photodetektor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Elektroden (21; 31) als interdigitale Fingerstruktur ausgelegt sind.4. Photodetector according to one of the preceding claims, characterized in that the electrodes (21; 31) are designed as an interdigital finger structure.
5. Verfahren zur Herstellung eines Photodetektors nach einem der vorhergehenden Ansprüche, mit den Schritten: - Herstellung einer leitenden Absorptionsschicht (32) auf einem isolierenden oder semiisolierenden Halbleitermaterial als Substrat (34) , - Herstellung von mindestens zwei Elektroden (31) als ohmsche Kontakte auf und/oder in der leitenden Absorptionsschicht (32) , - Modifizierung der leitenden Absorptionsschicht (32) zwischen den ohmschen Kontakten durch Ionen, so dass zwischen den Elektroden ein homogenes elektrisches Feld erzeugt werden kann, - Kontaktierung des Photodetektors.5. A method for producing a photodetector according to one of the preceding claims, comprising the steps of: - producing a conductive absorption layer (32) on an insulating or semi-insulating semiconductor material as the substrate (34), - producing at least two electrodes (31) as ohmic contacts and / or in the conductive absorption layer (32), - modification of the conductive absorption layer (32) between the ohmic contacts by ions so that a homogeneous electric field can be generated between the electrodes, - contacting the photodetector.
6. Verfahren nach vorhergehendem Patentanspruch, dadurch gekennzeichnet, dass die Absorptionsschicht (32) durch Ionenimplan- tation oder Eindiffusion von Dotierstoffen oder durch Epitaxie mit oder ohne Übergangsschicht hergestellt wird.6. The method according to the preceding claim, characterized in that the absorption layer (32) is produced by ion implantation or diffusion of dopants or by epitaxy with or without a transition layer.
7. Verfahren nach einem der Ansprüche 5 oder 6, dadurch gekennzeichnet, dass die ohmschen Kontakte (31) durch Aufbringen von geeigneten Metallschichten und/oder durch Einlegieren hergestellt werden.7. The method according to any one of claims 5 or 6, characterized in that that the ohmic contacts (31) are produced by applying suitable metal layers and / or by alloying.
8. Verfahren nach einem der Ansprüche 5 bis 7, dadurch gekennzeichnet, dass das die Elektroden (31) als Maske während der Implantation wirken.8. The method according to any one of claims 5 to 7, characterized in that the electrodes (31) act as a mask during the implantation.
9. Verfahren nach einem der Ansprüche 5 bis 8, dadurch gekennzeichnet, dass zuerst die hochohmige Absorptionsschicht erzeugt wird und anschließend die niederohmigen Bereiche unterhalb der noch herzustellenden ohmschen Kontakte mittels Ionenimplantation hergestellt werden. 9. The method according to any one of claims 5 to 8, characterized in that first the high-resistance absorption layer is produced and then the low-resistance regions below the ohmic contacts still to be produced are produced by means of ion implantation.
PCT/DE2004/001295 2003-07-24 2004-06-19 Photodetector and method for the production thereof WO2005011003A1 (en)

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US4998154A (en) * 1990-01-18 1991-03-05 Northern Telecom Limited MSM photodetector with superlattice
EP0651448A1 (en) * 1993-10-28 1995-05-03 Hitachi Europe Limited Improved metal-semiconductor-metal photodetector
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WO2000041456A2 (en) * 1999-01-12 2000-07-20 Forschungszentrum Jülich GmbH Optical detector with a filter layer made of porous silicon and method for the production thereof

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