WO1997005661A1 - Transistor a effet de champ dope par modulation, a structure d'arret modulee - Google Patents

Transistor a effet de champ dope par modulation, a structure d'arret modulee Download PDF

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Publication number
WO1997005661A1
WO1997005661A1 PCT/DE1996/001427 DE9601427W WO9705661A1 WO 1997005661 A1 WO1997005661 A1 WO 1997005661A1 DE 9601427 W DE9601427 W DE 9601427W WO 9705661 A1 WO9705661 A1 WO 9705661A1
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WO
WIPO (PCT)
Prior art keywords
barrier layer
modulation
effect transistor
field effect
doped field
Prior art date
Application number
PCT/DE1996/001427
Other languages
German (de)
English (en)
Inventor
Karl-Heinz Bachem
Lester F. Eastman
Original Assignee
Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. filed Critical Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority to EP96931731A priority Critical patent/EP0842542A1/fr
Publication of WO1997005661A1 publication Critical patent/WO1997005661A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/778—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface
    • H01L29/7782—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface with confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET
    • H01L29/7783—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface with confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET using III-V semiconductor material

Definitions

  • the invention relates to a modulation-doped field effect transistor with a channel layer, on which a barrier layer is applied, which is lattice-matched to the crystal structure of the channel layer, which is composed of a mixed crystal structure and has a doping.
  • Modulation-doped field effect transistors are further developed field effect transistors whose conductive channel through which the source / drain current flows is undoped, whereas the barrier layer adjoining the channel layer has dopants in a characteristic manner.
  • the doping is placed in the barrier layer, for example, in atomically sharp planes, so-called delta doping, so that the banding pattern in the barrier layer can be influenced in a characteristic manner, which, as will be explained in more detail later, also results in the banding pattern in ⁇ is "bent" within the channel area in such a way that energetic conditions result in this area, which preferably lead to the formation of 2-dimensional electron gas densities.
  • a special technical quality feature of MODFET Components is the very high achievable 2-dimensional electron gas density in the current-carrying channel area.
  • the electron gas density that forms limits the maximum current in the component given the width of the component and thus the channel, which essentially determines the microwave power available at the output of the component.
  • an essential aspect of the development work on MODFET components is aimed at developing semiconductor structures which permit the formation of ever larger 2-dimensional electron gas densities in the current-carrying channel region.
  • a second, essential quality criterion of the components in question is the dielectric strength of the barrier structure lying between the control electrodes and the channel area.
  • the dielectric strength of the barrier structure determines the operating voltage level of the component, which as a second factor significantly influences the microwave power available on the component.
  • the compound GalnP has become known for use for the barrier structure. It has been shown that the advantageously modified MODFET has better noise behavior than its predecessor and, moreover, is easier to manufacture.
  • the epitaxial deposition of the barrier layer is considerably simplified.
  • aluminum-free structures with the gas-phase epitaxy which is particularly suitable for mass production with organometallic source materials are easier to produce in the industrial sector.
  • the combination of phosphidic and arsenid layers in one structure offers advantages in terms of production technology, especially since certain etching selectivities can be advantageously used in the structuring of the components.
  • the invention is based on the object of further developing a modulation-doped field effect transistor with a channel layer on which a barrier layer which is matched to the crystal structure of the channel layer and which is composed of a mixed crystal structure and has a doping is applied, so that on the one hand the electron density determining the performance increase of the component is increased and on the other hand the breakdown voltage between the channel and the control electrode connections, which is also important for the quality of the component, is optimized.
  • These optimizations should, if possible, be carried out in such a way that the element aluminum, which has the disadvantages mentioned, can be dispensed with.
  • the production of such an optimized component should also be suitable for production on an industrial scale without great technical effort, so that the pro- production costs can be kept as low as possible.
  • an undoped buffer layer is on a semi-insulating substrate layer 1
  • layers 1 and 2 consist of GaAs. Of course, alternative substrate materials can also be used.
  • a barrier structure 4 which consists of GalnP, is applied to the channel layer 3 in a lattice-adapted manner.
  • a doped barrier region 5 is provided within the barrier structure 4 and is, for example, offset with suitable doping atoms within an atomically sharp plane in accordance with a delta doping.
  • Contact layers 6 made of highly doped GaAs are also provided on the barrier structure 4, on which the ohmic contacts 7 are provided for the source and drain connections. In the center of the ohmic contacts 7, a control electrode 8 made of metal is placed directly on the barrier structure 4, via which the gate voltage can be applied.
  • FIG. 2 shows the associated band diagram for the known MODFET structure shown in FIG. 1.
  • the energetic see tape runs through the layers 2 to 6 described above.
  • the axis of abscissa X represents the cross-sectional line through the layer structure, the energy values of the associated band profiles are plotted on the ordinate.
  • a lowering of the conduction band edge energy within the channel layer is to be carried out in a known manner by a targeted increase in the doping within the barrier structure.
  • the reference symbol ED represents the local and energetic position of the donor state introduced in isolation in the barrier layer structure 4.
  • the characteristic course of the conduction band edge energy between the channel layer 3 and the barrier structure 4 is commonly referred to as conduction band edge discontinuity, the size and nature of which can be derived from the Maxwellian relationships.
  • Dopant concentration is increased within the doping introduced locally in the barrier layer 4.
  • FIG. 3 top representation, in which a diagram representation comparable to FIG. 2 is shown.
  • the different band energy profiles a, b and c correspond to different levels of doping within the barrier layer 4, where b represents the highest doping.
  • the curve a corresponds to a vanishingly small doping in the barrier 4 (see also the very thin line for the donor state). In this case, channel 3 is almost free of charge carriers. For the curves b and c there are higher dopings accepted.
  • the conduction band edge energy in the channel now touches the Fermi level, see curve b, or is below the Fermi level, see curve c within the channel layer.
  • Curve c shows the case of the highest possible electron concentration within the channel layer. This case arises when the minimum of the conduction band edge energy within the barrier layer 4 is only a few lOmeV above the Fermi level.
  • a further increase in the electron concentration within the channel layer by increasing the doping is not possible, especially since a further increase in the doping would not allow the conduction band edge energy within the barrier structure to be set at the Fermi level. Rather, the conduction band drops below the Fermini level, as a result of which an electron gas would likewise form in the barrier layer in the vicinity of the minimum.
  • the above considerations are now based on the usual assumption that the ratio of gallium and indium within the barrier structure layer is 50% in each case. This relationship can also be seen from the lower representation in FIG. 3, from which the composition factor x of GaxInl-xP is plotted in relation to the barrier thickness.
  • the lattice-matched GalnP barrier layer 4 in which the Ga content is equal to the In content, can be replaced by a so-called pseudomorphic GaAnP barrier layer with an increased Ga content.
  • the Ga content has been increased uniformly in the entire barrier layer 3 by more than 50% content.
  • the use of this measure leads to the problem that an increase in the Ga content changes the lattice structure of the GalnP barrier material in such a way that lattice-adapted growth of the barrier layer material increased in the Ga content is not possible without lattice dislocations over large layer thicknesses.
  • the GaAs buffer layer has a cubic lattice cell structure
  • the modified GalnP lattice has a tetragonal lattice cell structure.
  • a growth of larger layer thicknesses on the buffer layer material is therefore not possible without the formation of internal mechanical crystal stresses, which relax when certain mechanical limit stresses are exceeded, i.e. the crystal lattice assumes its original lattice constant, which ultimately results in an unusable component.
  • the maximum growth thickness up to which no relaxation processes occur is also referred to as the critical layer thickness.
  • barrier layer Thicknesses of approximately 20 nm may therefore only be raised slightly above 50%, so that internal stresses are avoided as far as possible in order to adapt the critical layer thickness to the desired layer thickness. Due to the only slight increase in the Ga content, the above-described effect of increasing the bandgap is only very slight.
  • a modulation-doped field effect transistor with a channel layer, on which a barrier layer, which is lattice-matched to the crystal structure of the channel layer, is applied, which is composed of a mixed crystal structure and has a doping, is further developed in that the ratio of the element composition of the mixed crystal is such It is location-dependent that the ratio has an extreme value at least at one point within the barrier layer.
  • the Ga content of the mixed crystal within the barrier layer is location-dependent and is greatest at least in one area.
  • the invention has been recognized that by specifically introducing gallium within the barrier layer preferably at the areas where the conduction band edge energy has a minimum value in the case of a uniform distribution in the mixed crystal between Ga and In, the benefit being greatest. This is usually the case at the points within the barrier layer where the highest dopant concentrations are.
  • composition-modulated MODFET Due to the location-dependent composition of the mixed crystal composition within the barrier layer, the term composition-modulated MODFET has been created for the abbreviated description of the component.
  • FIG. 1 shows a schematic cross-sectional representation through a GalnP / GalnAs / GaAs MODFETs
  • FIG. 3 shows a band diagram of a GalnP / GalnAs / GaAs MODFET with a non-location-dependent chemical composition in the GalnP barrier layer;
  • FIG. 4 shows a band diagram of a MODFET modified according to the invention with a location-dependent chemical composition in the GalnP barrier layer; 5 alternative embodiment of the composition-modulated MODFET according to the invention;
  • composition-modulated barrier layer according to the invention.
  • FIGS. 1 and 2 show the layer structure and the conduction band energy curves of a typical modulation-doped field effect transistor.
  • an enlargement of the conduction band discontinuity and thus the increase in the distance between the conduction band energy can are carried out according to the invention within the barrier layer and the Fermi energy, by changing the gallium content within the barrier structure depending on the location.
  • the gallium content assumes a proportion factor of 75% only at a single point, in a local minimum, the gallium content being lower in the other areas.
  • a local maximum of the gallium content x which is also referred to as the composition factor x, it can be achieved that the average gallium content within the barrier structure 4 is increased only slightly above 50%, so that in this way a relatively high critical layer thickness can be achieved.
  • the conduction band energy curves with different doping within the barrier structure 4 shows the conduction band energy curves with different doping within the barrier structure 4.
  • the courses correspond to the band energies of the upper illustration in FIG. 3.
  • the band curve a corresponds to the lowest doping within the barrier layer 4
  • the band curve d corresponds to that with the highest doping.
  • the reduction in the conduction band energy within the channel layer 3 below the fermi energy can be increased considerably with the measure according to the invention. In this way, the 2-dimensional electron gas density within the channel layer 3 can be increased and, on the other hand, the breakdown voltage behavior of the barrier layer can be improved.
  • the measure according to the invention i.e. A targeted, location-dependent introduction of gallium within the barrier structure 4 thus considerably increases the band gap and thus also the distance of the conduction band edge from the Fermi level in the barrier exactly where it brings the greatest benefit in terms of component physics.
  • the local increase in the band gap in the bypass of the doped barrier region also allows the electron concentration in channel 3 to be increased by increasing the doping in the barrier.
  • FIG. 6 and 7 show band diagrams with constant doping in each case with variable control electrode potential VI to V4. These curves show how the channel density changes depending on the control voltage.
  • Fig. 6 the band course is assumed within a barrier 4 with a constant chemical composition. It can be seen that when the control electrode potential is lowered, the conduction band edges are shifted in the direction of the Fermini level.
  • FIG. 7 shows how the conditions change when a composition-modulated barrier according to the invention with a gallium distribution within the barrier layer 4 according to FIG. 4, bottom illustration, is used. The arrow shown in FIG. 7 illustrates the amount by which the tax electrode potential and thus the channel density is to be increased.
  • composition-modulated barrier according to the invention can be seen, in particular, in the fact that with only a moderate increase in the average Ga content in the barrier, the conduction band edge energy of the barrier in the critical, doped region can be increased substantially more than with a general increase in the Gallium content over the entire barrier thickness is possible. With the composition-modulated barrier according to the invention, the "critical layer thickness" can thus also be used more effectively.
  • composition-modulated barrier according to the invention is not only suitable for increasing the maximum electron concentration in the channel, but can also be used with a corresponding refinement of the composition profile to increase the dielectric strength of the barrier structure.
  • the upper dashed line in FIG. 8 corresponds to a conduction band course for a strongly negative control electrode potential
  • the lower dashed line corresponds to the conduction band energy with a strongly positive control electrode potential
  • the band diagrams represent composition-modulated barriers according to a gallium distribution according to FIG. 4, lower representation.
  • the upper continuous curve shape corresponds to the energetic conditions with a strong negative control electrode potential
  • the lower band shape with strongly positive control electrode potential. It can be seen that the tunnel barriers for electrons are always smaller with a uniformly distributed barrier material composition than with composition-modulated barriers.
  • the associated composition profile of the gallium content within the barrier layer 4, which is shown in FIG. 10, has two maxima, the first maximum in the doped region of the barrier and the second maximum below the control electrode.
  • the first maximum contributes to increasing the electron density in the channel, whereas the second maximum increases the tunnel barrier at a favorable point.
  • the gallium concentrations of the maxima must be coordinated with one another if the mean gallium concentration is chosen to be constant. The highest possible electron density and dielectric strength cannot be set simultaneously when using GalnP as a barrier material.
  • FIG. 12 shows a further variant of the composition modulation within the barrier layer.
  • the band gap is only increased below the control electrode.
  • This barrier profile would be chosen if a high maximum electron density in the channel is not required, for example in the case of low-noise small signal amplifiers, but the leakage currents of the control electrode are to be reduced.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Junction Field-Effect Transistors (AREA)

Abstract

L'invention concerne un transistor à effet de champ dopé par modulation, qui comprend une couche de canal (3) sur laquelle est appliquée une couche d'arrêt (4) adaptée en termes de réseau à la structure à cristal de la couche de canal. Cette couche d'arrêt est composée d'une structure à cristal mixte et comporte un dopage. La couche tampon (2) se compose notamment de GaAs, la couche de canal (3), de GaImAs et la couche d'arrêt (4), de GaxIn1-xP. L'invention se caractérise en ce que le rapport de la composition élémentaire du cristal mixte dépend de la position, de manière à ce que ledit rapport comporte au moins une valeur extrême en un point situé à l'intérieur de la couche d'arrêt (4). La teneur x en Ga du cristal mixte dépend notamment de la position à l'intérieur de la couche d'arrêt (4) et comporte au moins une zone dans laquelle x atteint une valeur maximale.
PCT/DE1996/001427 1995-08-01 1996-08-01 Transistor a effet de champ dope par modulation, a structure d'arret modulee WO1997005661A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP96931731A EP0842542A1 (fr) 1995-08-01 1996-08-01 Transistor a effet de champ dope par modulation, a structure d'arret modulee

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19528238.8 1995-08-01
DE1995128238 DE19528238C2 (de) 1995-08-01 1995-08-01 Modulationsdotierter Feldeffekttrasistor mit kompositionsmodulierter Barrierenstruktur

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WO1997005661A1 true WO1997005661A1 (fr) 1997-02-13

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0569259A2 (fr) * 1992-05-08 1993-11-10 The Furukawa Electric Co., Ltd. Transistor à effet de champ à barrière quantique multiple
FR2698722A1 (fr) * 1992-11-30 1994-06-03 Fujitsu Ltd Dispositif à composé semi-conducteur des groupes III-V du type d'un transistor à mobilité électronique élevée.
JPH06244218A (ja) * 1993-02-22 1994-09-02 Sumitomo Electric Ind Ltd 化合物半導体装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0569259A2 (fr) * 1992-05-08 1993-11-10 The Furukawa Electric Co., Ltd. Transistor à effet de champ à barrière quantique multiple
FR2698722A1 (fr) * 1992-11-30 1994-06-03 Fujitsu Ltd Dispositif à composé semi-conducteur des groupes III-V du type d'un transistor à mobilité électronique élevée.
JPH06244218A (ja) * 1993-02-22 1994-09-02 Sumitomo Electric Ind Ltd 化合物半導体装置

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
J. DICKMANN ET AL.: "(Al0.7Ga0.3)0.5In0.5P/In0.15Ga0.85As/GaAs heterostructure field effect transistors with very thin highly p-doped surface layer", IEEE TRANSACTIONS ON ELECTRON DEVICES, vol. 42, no. 1, January 1995 (1995-01-01), NEW YORK US, pages 2 - 7, XP002020815 *
L.M. JELLOIAN ET AL.: "InP-based HEMT's with Al0.48In0.52AsxP1-x Schottky layers", IEEE ELECTRON DEVICE LETTERS, vol. 15, no. 5, May 1994 (1994-05-01), NEW YORK US, pages 172 - 174, XP002020816 *
PATENT ABSTRACTS OF JAPAN vol. 18, no. 626 (E - 1636) 29 November 1994 (1994-11-29) *

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DE19528238A1 (de) 1997-02-06
DE19528238C2 (de) 1999-07-22
EP0842542A1 (fr) 1998-05-20

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