WO2015176002A1 - Dopage dans des dispositifs à base de nitrure iii - Google Patents

Dopage dans des dispositifs à base de nitrure iii Download PDF

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WO2015176002A1
WO2015176002A1 PCT/US2015/031190 US2015031190W WO2015176002A1 WO 2015176002 A1 WO2015176002 A1 WO 2015176002A1 US 2015031190 W US2015031190 W US 2015031190W WO 2015176002 A1 WO2015176002 A1 WO 2015176002A1
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layers
doped
light
nitride
layer
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Nathan G. YOUNG
Robert M. Farrell
Claude C.A. Weisbuch
James S. Speck
Steven P. Denbaars
Umesh K. Mishra
Shuji Nakamura
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University of California Berkeley
University of California San Diego UCSD
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University of California San Diego UCSD
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    • 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
    • H10D62/85—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group III-V materials, e.g. GaAs
    • H10D62/854—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group III-V materials, e.g. GaAs further characterised by the dopants
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D10/00—Bipolar junction transistors [BJT]
    • H10D10/80—Heterojunction BJTs
    • H10D10/821—Vertical heterojunction BJTs
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D30/00—Field-effect transistors [FET]
    • H10D30/40—FETs having zero-dimensional [0D], one-dimensional [1D] or two-dimensional [2D] charge carrier gas channels
    • H10D30/47—FETs having zero-dimensional [0D], one-dimensional [1D] or two-dimensional [2D] charge carrier gas channels having two-dimensional [2D] charge carrier gas channels, e.g. nanoribbon FETs or high electron mobility transistors [HEMT]
    • H10D30/471—High electron mobility transistors [HEMT] or high hole mobility transistors [HHMT]
    • H10D30/475—High electron mobility transistors [HEMT] or high hole mobility transistors [HHMT] having wider bandgap layer formed on top of lower bandgap active layer, e.g. undoped barrier HEMTs such as i-AlGaN/GaN HEMTs
    • H10D30/4755—High electron mobility transistors [HEMT] or high hole mobility transistors [HHMT] having wider bandgap layer formed on top of lower bandgap active layer, e.g. undoped barrier HEMTs such as i-AlGaN/GaN HEMTs having wide bandgap charge-carrier supplying layers, e.g. modulation doped HEMTs such as n-AlGaAs/GaAs HEMTs
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D30/00—Field-effect transistors [FET]
    • H10D30/40—FETs having zero-dimensional [0D], one-dimensional [1D] or two-dimensional [2D] charge carrier gas channels
    • H10D30/47—FETs having zero-dimensional [0D], one-dimensional [1D] or two-dimensional [2D] charge carrier gas channels having two-dimensional [2D] charge carrier gas channels, e.g. nanoribbon FETs or high electron mobility transistors [HEMT]
    • H10D30/471—High electron mobility transistors [HEMT] or high hole mobility transistors [HHMT]
    • H10D30/477—Vertical HEMTs or vertical HHMTs
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D30/00—Field-effect transistors [FET]
    • H10D30/80—FETs having rectifying junction gate electrodes
    • H10D30/87—FETs having Schottky gate electrodes, e.g. metal-semiconductor FETs [MESFET]
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/81—Bodies
    • H10H20/822—Materials of the light-emitting regions
    • H10H20/824—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP
    • H10H20/825—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP containing nitrogen, e.g. GaN
    • H10H20/8252—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP containing nitrogen, e.g. GaN characterised by the dopants
    • 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
    • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
    • H10D62/113—Isolations within a component, i.e. internal isolations
    • 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
    • H10D62/85—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group III-V materials, e.g. GaAs
    • H10D62/8503—Nitride Group III-V materials, e.g. AlN or GaN

Definitions

  • the net polarization in the active region is greater than zero and in the opposite sense to the built-in field due to the p-n or n-p junction.
  • the impurity doping profile can be designed so that the built-in field effectively screens the polarization field, resulting in a near zero net field in the active region of a properly doped device.
  • the present invention describes doping in Ill-nitride devices.
  • Germanium is a more suitable dopant for highly doped layers in Ill-nitride electronic devices, especially transistors involved in high voltage, high power or high frequency operation, such as high electron mobility transistors (HEMTs), current aperture vertical electron transistors (CAVETs), heterojunction bipolar transistors (HBTs), metal-semiconductor field effect transistors (MESFETs) or junction field effect transistor (JFETs).
  • HEMTs high electron mobility transistors
  • CAVETs current aperture vertical electron transistors
  • HBTs heterojunction bipolar transistors
  • MESFETs metal-semiconductor field effect transistors
  • JFETs junction field effect transistor
  • FIG. 3 is a graph of the simulated dependence of the square of the
  • FIG. 9 is a schematic representation of a Ill-nitride metal-semiconductor field effect transistor (MESFET).
  • MESFET Ill-nitride metal-semiconductor field effect transistor
  • FIG. 14 is a schematic representation of a Ill-nitride CAVET with a GaN:Ge layer in the AlGaN barrier region above the channel.
  • This invention describes a structure for improving the performance of c-plane (0001) III -nitride light-emitting or light-absorbing devices.
  • LEDs Ill-nitride light emitting diodes
  • LDs laser diodes
  • Reducing or eliminating polarization-induced electric fields in the active region of c- plane devices should significantly improve device performance.
  • the net polarization in the active region is greater than zero, which can lead to a reduction in electron-hole wavefunction overlap in the active layer and a corresponding decrease in radiative rate which results in diminished radiative efficiency.
  • the polarization field is in the opposite sense to the built-in field due to the p-n junction. Therefore, in the growth of c-plane devices, the impurity doping profile can be designed so that the built-in field effectively screens the polarization field, resulting in a near zero net field in the active region of a properly doped device. These doping profiles can be designed so the net field is near zero for current densities of interest for device operation.
  • FIG. 1 shows a cross-sectional schematic of the (0001) SQW LED structure 100.
  • This structure 100 was used for simulating the effects of QW thickness and doping on the net electric field and wavefunction overlap in the active region.
  • the low doping in the barrier layers will not screen the polarization fields in the QW.
  • the ground state electron and hole wavefunctions are pressed together by the wide bandgap barrier confinement even though the electric field in the QW is very high.
  • the field is nearly flat in the middle of the QW, but increases significantly at the right and left edges, causing the electron and hole ground state wavefunctions to be confined at the edges of the well rather than spreading across the entire width of the well.
  • Well-designed n-type and p-type barrier layer doping is necessary to fully screen the polarization charges at the QW interfaces and flatten the electric field in the QW, thereby increasing wavefunction overlap.
  • FIG. 3 summarizes the simulated dependence of the square of the wavefunction overlap on current density for LEDs with a range of active region thicknesses and no intentional barrier layer doping.
  • the LEDs with QW thicknesses of 3, 5, and 8 nm exhibited wavefunction overlap that increased monotonically as a function of current density.
  • the LED with a thickness of 12 nm exhibited nearly zero wavefunction overlap with little dependence on current density.
  • FIG. 4(a) shows that even with n and p barrier layer doping of IE 19 cm “3 , there is little difference from the undoped case (FIG. 3): the electric field in the QW is still in the opposite sense to the built-in field since the polarization field remains largely unscreened, and this leads to a spatial separation of the ground state electron and hole wavefunctions, yielding a near zero wavefunction overlap.
  • FIG. 4(b) shows that upon increasing the doping to 4E19 cm "3 , the electric field in the QW begins to decrease and the energy bands begin to flatten, bringing the electron and hole wavefunctions closer together and increasing the overlap, though it is apparent that the
  • FIG. 4(d) once again shows some spatial separation between the electron and hole wavefunctions and a non-zero electric field in the QW.
  • the doping level of 1E20 cm "3 was high enough to be degenerate on the n- side of the QW and cause an accumulation of electrons.
  • FIG. 5 summarizes the simulated dependence of the square of the
  • the LED with a doping level of IE 19 cm “3 exhibited nearly zero wavefunction overlap over a large range of current densities.
  • the LED with a doping of 4E17 cm “3 exhibited a relatively low but non-zero wavefunction overlap that increased monotonically with increasing current density.
  • the LED with a doping level of 1E20 cm “3 showed a similar, albeit much higher, dependence of the wavefunction overlap on current density.
  • the above section described a structure for decreasing the net electric field in the active region of a (0001) SQW LED.
  • the scope of this invention also covers the N-face (000-1) orientation when used in an n-p junction, with the p-type material underneath the active region so that the polarization is in the opposite sense to the built-in field due to the n-p junction.
  • This idea is also pertinent to Ill-nitride devices with multiple quantum well (MQW) active regions, active regions with QWs of any thickness, active regions with QWs of any alloy composition, active regions with QWs of a graded alloy composition, active regions with barriers of any thickness, active regions with barriers of any alloy composition, and active regions with barriers of a graded alloy composition.
  • MQW multiple quantum well
  • the scope of this invention also covers Ill-nitride devices with doping profiles other than the profile cited above in the technical description.
  • the LED cited above in the technical description had 10 nm n-type and p-type doped layers that were immediately adjacent to the light-emitting layers in the active region.
  • the scope of this invention also covers doped layers that are offset slightly (e.g. more than 1 nm) from the light-emitting layers. Offsetting the doped layers decreases the effectiveness of the polarization screening, but may be necessary for other reasons related to the device growth or fabrication. This idea is also pertinent to doped layers that are offset by asymmetric distances from the light-emitting layers, doped layers with asymmetric doping levels, doped layers with graded doping profiles, and doped layers of asymmetric thicknesses.
  • the scope of this invention also covers Ill-nitride devices with MQW active regions where the layers between light-emitting QWs (referred to hereafter as internal barrier layers) are intentionally doped.
  • internal barrier layers In a MQW active region there is more than one pair of polarization sheet charge layers, each of which must be compensated in order to screen the electric field in all of the light emitting QW layers.
  • Doping of internal barrier layers, which are immediately adjacent to QWs in the MQW active region may be more effective at screening polarization-induced fields in a MQW active region than only doping layers outside of the active region. This idea is pertinent to cases where all internal barrier layers between QWs are intentionally doped, where some internal barrier layers are intentionally doped and others are not, where one or more internal barrier layers are intentionally doped by different amounts, and where internal barrier layers have graded doping profiles.
  • substrates other than free-standing c-plane GaN could be used for
  • III -nitride thin film growth includes the growth of III- nitride thin films on all possible crystallographic orientations of all possible foreign substrates.
  • These foreign substrates include, but are not limited to, sapphire, silicon carbide, silicon, zinc oxide, boron nitride, lithium aluminate, lithium niobate, germanium, aluminum nitride, lithium gallate, partially substituted spinels, and quaternary tetragonal oxides sharing the y-LiA10 2 structure.
  • c-plane III -nitride nucleation (or buffer) layers and nucleation layer growth methods are acceptable for the practice of this invention.
  • the growth temperature, growth pressure, orientation, and composition of the nucleation layers need not match the growth temperature, growth pressure, orientation, and composition of the subsequent thin films and heterostructures.
  • the scope of this invention includes the growth of c-plane Ill-nitride thin films on all possible substrates using all possible nucleation layers and nucleation layer growth methods.
  • the scope of this invention also covers c-plane Ill-nitride thin films grown on epitaxial laterally overgrown (ELO) Ill-nitride templates.
  • the ELO technique is a method of reducing the density of threading dislocations (TD) in subsequent epitaxial layers. Reducing the TD density leads to improvements in device performance. For c-plane Ill-nitride LEDs and LDs, these improvements include increased output powers, increased internal quantum efficiencies, longer device lifetimes, and reduced threshold current densities. [Ref. 10]
  • a high electron mobility transistor is one type power semiconductor device that can be fabricated based on Ill-nitride materials.
  • a GaN HEMT device can include a Ill-nitride semiconductor body with at least two III -nitride layers formed thereon. Different materials formed on the body or on a buffer layer causes the layers to have different band gaps. The different materials in the adjacent Ill-nitride layers also causes polarization, which contributes to a conductive two-dimensional electron gas (2DEG) region near the junction of the two layers, specifically in the layer with the narrower band gap.
  • 2DEG conductive two-dimensional electron gas
  • One of the layers through which current is conducted is the channel layer.
  • the narrower band gap layer in which the current carrying channel, or the 2DEG is located is referred to as the channel layer.
  • FIG. 6 shows a standard Ga-face GaN HEMT structure 600 comprised of a substrate 602, GaN buffer layer 604, Al x Gai_ x N layer 606, source (S) 608, drain (D) 610 and gate (G) 612.
  • the substrate 600 may be GaN, SiC, sapphire, Si, or any other suitable substrate for GaN device technology.
  • the conducting channel is comprised of a 2DEG 614 formed in the GaN layer 604 near the interface with the Al x Gai_ x N layer 606, which is shown as a dotted line in FIG. 6.
  • the region between the source 608 and gate 612 is referred to as the source access region, and the region between the drain 610 and gate 612 is referred to as the drain access region.
  • the barrier layer (for example, AlGaAs on GaAs) must be doped in order to pull the conduction band energy down far enough to form a 2DEG at the heterointerface.
  • the delta-doped sheet or doped region is usually separated from the heterointerface by an undoped cap layer.
  • the barrier layer is often left undoped since a 2DEG forms naturally due to polarization. This allows for higher channel mobility due to the lack of ionized impurity scattering. In this case, the charge in the channel comes from surface donor states.
  • One method of overcoming the problems presented by surface donor states is to dope the barrier layer with an n-type dopant.
  • This doping can take the form of a delta-doped layer or a thicker region of the barrier layer.
  • There is a trade-off involved in the placement of this doped layer The closer the donors are to the channel, the more charge they can contribute because surface states are also competing for charges.
  • having donors close to the channel decreases the channel mobility due to ionized impurity scattering.
  • a current aperture vertical electron transistor (CAVET) is another type power semiconductor device that can be fabricated based on Ill-nitride materials.
  • FIG. 7 is a schematic illustration of a CAVET 700, including higher/heavily n-type doped GaN (n+ -GaN) 702, lower or lightly n-type doped GaN (n ⁇ - GaN) 704, aperture 706, Current Blocking Layer (CBL) 708, unintentionally doped (UID) GaN 710, Al x Gai_ x N 712, source (S) 714, gate (G) 716, and drain (D) 718.
  • the CAVET 700 is a vertical device comprised of an n-type doped drift region to hold voltage and a horizontal 2DEG 720 to carry current flowing from the source 714, under a planar gate 716, and then in a vertical direction to the drain 718 through the aperture 706.
  • CAVET 700 A fundamental part of a CAVET 700 is the CBL 708, which blocks the flow of the current and causes on-state current to flow through the aperture 706.
  • a CAVET 's performance relies on high frequency modulation of current in a 2DEG channel 720.
  • the same issues of dispersion apply, and it is desirable to dope the AlGaN barrier 712 in such a way as to provide charge to the channel 720 while avoiding impurity scattering.
  • a heterojunction bipolar transistor is another type of power semiconductor device that can be fabricated based on Ill-nitride materials.
  • FIG. 8 is a schematic illustration of an HBT 800, including an n-type doped GaN emitter region 802, a p-type doped GaN base region 804, a lightly n-type doped GaN collector region 806, a heavily n-type doped GaN sub-collector region 808, and emitter 810, base 812, and drain 814 contacts.
  • the substrate 816 may be GaN, SiC, sapphire, Si, or any other suitable substrate for GaN device technology.
  • the HBT 800 is a vertical device comprised of an n-type emitter region 802, a p-type base region 804, and an n- type collector region 806. Electrons are provided by the emitter 810 and they flow across the base 812 and to the collector 814. On-state current flows in the device 800 when the emitter-base junction is forward biased, and the base-collector junction is reverse biased. It is desirable to have a structure with a heavily n-doped sub-collector region 808 for low contact resistance, but to also avoid adding strain to the subsequent layers during growth.
  • a metal-semiconductor field effect transistor (MESFET) or junction field effect transistor (JFET) is another type power semiconductor device that can be fabricated based on Ill-nitride materials.
  • MESFET metal-semiconductor field effect transistor
  • JFET junction field effect transistor
  • FIG. 9 is a schematic illustration of a MESFET 900 with a lightly n-type doped GaN channel region 902, a source 904, a drain 906, and a gate 908.
  • the substrate 910 may be GaN, SiC, sapphire, Si, or any other suitable substrate for GaN device technology. Electrons flow through the channel region 902 from source 904 to drain 906 when the bias on the gate 908 is such that the channel 902 is not completely depleted.
  • the channel region 902 in a MESFET must be doped in order to ensure a low turn-on voltage; however, it is desirable to have high mobility in the channel 902. Doping tends to lower mobility due to ionized impurity scattering, so it would be desirable to use an n-type dopant in the channel 902 with a high mobility at the same doping concentration.
  • Ill-nitride electronic devices such as HEMTs, CAVETs, HBTs, and
  • the present invention discloses Ill-nitride electronic devices with n-type layers doped with germanium. Germanium has been shown to not add significant strain to a GaN lattice while maintaining smooth morphology beyond a concentration of 1E20 cm 3 . Consequently, germanium is a more suitable dopant for highly doped layers in Ill-nitride electronic devices, such as HEMTs, CAVETs, HBTs, and
  • This invention describes a structure for improving the performance and reliability of Ill-nitride electronic devices, especially transistors involved in high voltage, high power, or high frequency operation in such applications, where the use of Ill-nitride materials would be suitable. Many such devices suffer from a problem known as dispersion, in which the output power at high frequency operation is significantly lower than at DC operation. Properly placed doped layers can help overcome the problem of dispersion.
  • a highly doped layer in the wide bandgap barrier of a HEMT device replaces surface states as the source of charge in the channel of the transistor, which is comprised of a 2DEG formed because of the band discontinuity at the heterostructure interface between channel material and the wider bandgap barrier material. This prevents dispersion, which is thought to be caused by surface traps.
  • the doped layer could be placed closer to the channel, separated by a wide bandgap cap layer, allowing higher charge concentration, or further from the channel with the same charge concentration, allowing higher mobility.
  • Ge doping can also be applied to a gate-recessed HEMT just above the AlGaN barrier, which is contacted by the gate, and below the AlGaN cap, which screens the channel from the surface states that cause dispersion.
  • Ge can be used in place of Si in highly doped layers in vertical transistor devices.
  • the highly n-type layer that makes contact with the backside drain electrode can be improved using Ge doping.
  • the sub-collector layer can be improved using Ge doping. It needs to be highly n-type to spread current laterally and make low resistance contact to the collector electrode. At the same dopant concentration, there will be less strain added and better morphology than in a Si-doped layer. This will improve the layers grown above it and lead to better overall device performance.
  • the inventors measured the properties of GaN:Ge layers grown by MOCVD by Hall measurements using a special epitaxial structure and measurement system, shown in FIGS. 10(a) and 10(b).
  • the epitaxial structure 1000 shown in FIG. 10(a) is comprised of a sapphire substrate 1002, a thick layer of intrinsic GaN 1004 (4 ⁇ in this case) for isolation of a top conductive GaN:Ge layer 1006, which must be thick enough to provide low resistance (300 nm in this case), and metal contacts 1008.
  • FIG. 10(b) shows a top-down view of the sample 1000 prepared for van-der Pauw resistivity and Hall effect measurements.
  • FIG. 11 shows the dependence of carrier concentration and mobility on the IBGe flow rate during growth of the GaN:Ge layer 1006 in the structure 1000 from FIG. 10(a). IBGe flow rates were varied in the study from 0.06 seem to 10 seem.
  • Carrier concentration is assumed to be equal to Ge concentration due to the low donor activation energy of Ge in GaN.
  • Molar flow ratios of Ge to Ga ranged between 0.0026 and 0.44, and resulting carrier concentrations (Ge concentrations) ranged between 8.8E17 cm “3 to 1.3E20 cm “3 , respectively.
  • the mobility ranged from 337 to 109 cm 2 /V s.
  • the mobility of GaN:Ge is higher than that of GaN:Si. [Ref. 12] This is likely the result of the Ge atom closer size than the Si atom to the Ga atom that it replaces in the GaN lattice. The size similarity results in less impurity scattering, which would decrease mobility.
  • Higher mobility in n-doped GaN:Ge layers compared to GaN: Si layers in III -nitride semiconductor devices would benefit performance in terms of speed and power.
  • a Ge doped layer can be added to the Al x Gai_ x N barrier region of the III- nitride HEMT from FIG. 6.
  • This device 1200 is shown in FIGS. 12(a) and 12(b), and is comprised of a substrate 1202, GaN buffer 1204, Al x Gai_ x N 1206, Al x Gai_ x N:Ge 1208, source 1210, drain 1212 and gate 1214.
  • the Al x Gai_ x N:Ge layer 1208 can comprise either a layer of defined thickness that makes up part or all of the Al x Gai_ x N barrier region 1206 shown in FIG. 12(a), or a delta-doped layer 1208 represented by a dotted line in FIG. 12(b).
  • Doping in the barrier region 1206, 1208 will eliminate dependence on surface states for supplying charge to the 2DEG channel 1216 as well as the dispersion and poor reliability and reproducibility of processing that plague HEMTs with undoped barriers.
  • the advantage of a delta-doped layer or thin doped layer is that the donors can be located on average closer to the channel 1216 and therefore give more of their charge to the channel 1216 instead of to surface states. This results in a higher channel carrier concentration.
  • the main advantage of Ge instead of Si in the n-doped layer 1208 is that a higher concentration of Ge can be supported in the layer 1208 without adverse strain effects or morphological breakdown. Therefore, the doped layer 1208 can be separated by a greater distance from the channel 1216, causing less ionized impurity scattering and leading to a higher mobility.
  • An A1N spacer layer can be optionally added at the barrier/channel interface in order to better confine charges in the 2DEG channel 1216 as well as reduce ionized impurity scattering in the channel 1216, and should be between 0.5 and 2 nm thick.
  • an additional undoped AlGaN layer may be added before the Ge doped AlGaN layer 1208 to provide additional separation between dopant atoms and the channel.
  • a 1 nm A1N spacer may be followed by a 3 nm Alo.2Gao.8N layer before a delta doped sheet charge where the Ge concentration is above IE 13 cm "2 .
  • FIG. 13 Another method of overcoming the problems presented by surface donor states is the deep-recessed GaN HEMT 1300 design shown in FIG. 13, which includes a substrate 1302, GaN buffer 1304, Al x Gai_ x N layer 1306, Al y Gai_ y N layer 1308, Al x Gai_ x N:Ge layer 1310, source 1312, drain 1314 and gate 1316.
  • a thick cap layer of GaN or Al y Gai_ y N 1308 isolates the surface from the 2DEG channel 1318, while a selective etch allows the gate 1316 metal to be deposited on a thin Al x Gai_ x N barrier 1306.
  • x and y can, but need not, be the same.
  • Charge is supplied to the channel 1318 by a highly n-doped layer 1310 (delta-doped or with a small thickness) at the interface between the Al x Gai_ x N layer 1306 and the Al y Gai_ y N layer 1308.
  • This layer 1310 can be Ge doped to reduce impurity scattering in the channel 1318 again by increasing the Al x Gai_ x N barrier 1306 thickness while maintaining the same channel 1318 carrier concentration without morphological degradation or increase in strain.
  • a Ge doped layer can be added to the Al x Gai_ x N barrier region of the III- nitride CAVET from FIG. 6.
  • Such a device 1400 is shown schematically in FIG. 14, and includes a higher/heavily n-type doped GaN (n+ -GaN) layer 1402, a lower or lightly n-type doped GaN (n ⁇ -GaN) layer 1404, an aperture 1406, a Current Blocking Layer (CBL) 1408, an unintentionally doped (UID) GaN layer 1410, an Al x Gai_ x N layer 1412, an Al x Gai_ x N:Ge layer 1414, source 1416, gate 1418, and drain 1420.
  • CBL Current Blocking Layer
  • the CAVET 1400 is a vertical device comprised of an n-type doped drift region to hold voltage and a horizontal 2DEG 1422 to carry current flowing from the source 1416, under the planar gate 1418, and then in a vertical direction to the drain 1420 through the aperture 1406.
  • the Al x Gai_ x N:Ge layer 1414 can comprise either a layer of defined thickness that makes up part or all of the Al x Gai_ x N barrier region 1412 or a delta-doped layer like the one depicted in the HEMT in FIG. 12(b). Doping in the barrier region 1412 will eliminate dependence on surface states for supplying charge to the channel 1422 as well as the dispersion and poor reliability and reproducibility of processing that plague CAVETs with undoped barriers. Like in the case of the HEMT, the main advantage of Ge instead of Si in the n-doped layer 1414 is that a higher concentration of Ge can be supported in the layer without adverse strain effects or morphological breakdown.
  • the doped layer 1414 can be separated by a greater distance from the channel 1422, causing less ionized impurity scattering and leading to a higher mobility.
  • an A1N spacer layer can be optionally added at the barrier/channel interface of the CAVET 1400 in order to better confine charges in the 2DEG channel 1422 as well as reduce ionized impurity scattering in the channel 1422, and should be between 0.5 and 2 nm thick.
  • the CBLs 1408 are a fundamental part of the CAVET structure 1400. They can be made from any layer that will block vertical current flow, such as a buried dielectric layer, a buried p-GaN layer, or a buried AlGaN layer. The remaining structure must be regrown on top of the buried layer after patterning and etching an opening for the aperture 1406.
  • Ge doping can also be incorporated into the sub-collector of an HBT 800, shown in FIG. 8. Since an HBT is a vertical device, it must have a highly n-doped layer below the collector. The more highly this layer can be doped, the lower the contact resistance between the layer and the collector contact.
  • the main advantage of Ge instead of Si in the sub-collector is that a higher concentration of Ge can be supported without adverse strain effects or morphological breakdown. The strain state of the layers above the sub-collector is important for device performance and high quality epitaxial growth. With Ge, this layer can be doped between 5E18 cm “3 and 1E20 cm "3 . Ge doping can also be incorporated into the GaN channel region of a
  • MESFET 9000 shown in FIG. 9.
  • the channel is this device is doped lightly n-type. It is desirable to maximize the mobility in the channel while maintaining a low turn-on voltage.
  • the advantage of doping with Ge instead of Si in the GaN channel region is that for the same doping level, and hence the same turn-on voltage, the mobility should be higher, as we have seen from comparing mobility values for GaN:Ge from FIG. 11 to known mobility values for GaN: Si.
  • Ge doping in the channel should be in the range from 1E16 cm "3 and 1E18 cm "3 .
  • Typical material growth methods for the GaN devices include but are not limited to MOCVD and MBE. Additionally, certain device structure improvements that benefit all embodiments are described. These can be applied to each of the embodiments, either together or one at a time.
  • the devices are passivated by a suitable dielectric, such as SiN. Passivation by SiN or a suitable dielectric can minimize the effect of trapped charge and ensure good device operation.
  • field plating by single or multiple field plates is included, which increase the breakdown voltage of the device and further minimizes the impact of trapping by reducing the peak electric field near the gate. Field plates (either separate or in conjunction with forming the gate layer) can be used for obtaining high breakdown voltages. In particular, slant field plates can maximize the benefits of the field plates.
  • a gate insulator is under the gate. The insulator reduces or eliminates the gate leakage current.
  • the scope of this invention also covers devices in the N-face (000-1) orientation when the AlGaN back barrier lies underneath the GaN channel and the GaN:Ge sheet doping layer is located between the AlGaN back barrier and the GaN buffer.
  • Heavy n-type doping above IE 13 cm "2 in this layer prevents the formation of a 2-dimentional hole gas at the back barrier/buffer interface, which would act as a parasitic channel.
  • Ge as an n-type dopant is advantageous compared to Si because a higher concentration of Ge can be supported without adverse strain effects or morphological breakdown.
  • the strain state of the layers above the sub-collector is important for device performance and high quality epitaxial growth.
  • Nonpolar planes include the ⁇ 11-20 ⁇ planes, known collectively as a-planes, and the ⁇ 10-10 ⁇ planes, known collectively as m-planes. Such planes contain equal numbers of gallium and nitrogen atoms per plane and are charge- neutral.
  • the term "semipolar plane" can be used to refer to any plane that cannot be classified as c-plane, a-plane, or m-plane. In crystallographic terms, a semipolar plane would be any plane that has at least two nonzero h, i, or k Miller indices and a nonzero 1 Miller index.
  • the scope of this invention also covers Ill-nitride devices with doping profiles other than the profile cited in the technical description.
  • the Ge doped layer in the barrier of a HEMT or CAVET can be of any reasonable thickness, from a delta-doped layer to several tens of nanometers.
  • the Ge doped layer can be offset from the channel by any reasonable distance, up to several tens of nanometers and at a minimum 1 nm.
  • An ideal position of the GaN:Ge can be found in the barrier region that maximizes the charge in the channel and the mobility of the channel.
  • Doping in the GaN:Ge layer can be graded. There can be multiple GaN:Ge layers in the barrier region.
  • Additional impurities or dopants can also be incorporated into the c-plane III- nitride thin films described in this invention.
  • Fe, Mg, Si, Ge, and Zn are frequently added to various layers in III -nitride heterostructures to alter the conduction properties of those and adjacent layers.
  • dopants and others not listed here are within the scope of the invention.
  • substrates other than free-standing c-plane GaN could be used for III -nitride thin film growth.
  • the scope of this invention includes the growth of III- nitride thin films on all possible crystallographic orientations of all possible foreign substrates.
  • These foreign substrates include, but are not limited to, sapphire, silicon carbide, silicon, zinc oxide, boron nitride, lithium aluminate, lithium niobate, germanium, aluminum nitride, lithium gallate, partially substituted spinels, and quaternary tetragonal oxides sharing the y-LiA10 2 structure.
  • c-plane III -nitride nucleation (or buffer) layers and nucleation layer growth methods are acceptable for the practice of this invention.
  • the growth temperature, growth pressure, orientation, and composition of the nucleation layers need not match the growth temperature, growth pressure, orientation, and composition of the subsequent thin films and heterostructures.
  • the scope of this invention includes the growth of c-plane Ill-nitride thin films on all possible substrates using all possible nucleation layers and nucleation layer growth methods.
  • these terms as used herein are intended to be broadly construed to include respective nitrides of the single species, Ga, Al, In and B, as well as binary, ternary and quaternary compositions of such Group III metal species. Accordingly, these terms include, but are not limited to, the compounds of A1N, GaN, InN, AlGaN, AlInN, InGaN, and AlGalnN.
  • compositions including stoichiometric proportions as well as off-stoichiometric proportions (with respect to the relative mole fractions present of each of the (Ga, Al, In, B)N component species that are present in the composition), can be employed within the broad scope of this invention.
  • compositions and materials within the scope of the invention may further include quantities of dopants and/or other impurity materials and/or other inclusional materials.
  • This invention also covers the selection of particular crystal orientations, directions, terminations and polarities of Group-Ill nitrides.
  • braces, ⁇ ⁇ denotes a set of symmetry-equivalent planes, which are represented by the use of parentheses, ( ).
  • brackets, [ ] denotes a direction
  • brackets, ⁇ > denotes a set of symmetry-equivalent directions.
  • Group-Ill nitride devices are grown along a polar orientation, namely a c-plane ⁇ 0001 ⁇ of the crystal, although this results in an undesirable quantum- confined Stark effect (QCSE), due to the existence of strong piezoelectric and spontaneous polarizations.
  • QCSE quantum- confined Stark effect
  • One approach to decreasing polarization effects in Group- Ill nitride devices is to grow the devices along nonpolar or semipolar orientations of the crystal.

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Abstract

L'invention concerne le dopage dans des dispositifs à base de nitrure III, qui peut être utilisé pour la détection efficace de champ de polarisation, les couches dopées étant adjacentes aux limites les plus externes de couches photoémettrices, ou les couches dopées étant décalées de plus de 1 nm par rapport aux limites les plus éloignées des couches photoémettrices, ou les couches dopées dans une région active à puits quantiques multiples comprenant les couches photoémettrices. En outre, du germanium (Ge) peut être utilisé en tant que dopant de type n dans des couches de nitrure III très dopées, car il n'ajoute pas de contrainte significative à un réseau de nitrure du Groupe III tout en maintenant une morphologie souple au-delà d'une concentration de 1E20 cm-3.
PCT/US2015/031190 2014-05-15 2015-05-15 Dopage dans des dispositifs à base de nitrure iii Ceased WO2015176002A1 (fr)

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CN107154435A (zh) * 2017-03-29 2017-09-12 西安电子科技大学 阶梯电流阻挡层垂直型功率器件
CN108962981A (zh) * 2018-07-13 2018-12-07 北京大学 一种降低氮化镓基外延层中漏电的结构及其制备方法
TWI650861B (zh) * 2016-09-28 2019-02-11 日商豐田自動車股份有限公司 半導體裝置及其製造方法
WO2019242100A1 (fr) * 2018-06-22 2019-12-26 中国科学院苏州纳米技术与纳米仿生研究所 Dispositif électronique à semi-conducteur d'oxyde de gallium à structure verticale et son procédé de fabrication
EP3900054A4 (fr) * 2018-12-21 2022-09-21 HRL Laboratories LLC Structure de diode cryogénique à faible tension d'attaque grille-cathode

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TWI650861B (zh) * 2016-09-28 2019-02-11 日商豐田自動車股份有限公司 半導體裝置及其製造方法
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CN108962981A (zh) * 2018-07-13 2018-12-07 北京大学 一种降低氮化镓基外延层中漏电的结构及其制备方法
EP3900054A4 (fr) * 2018-12-21 2022-09-21 HRL Laboratories LLC Structure de diode cryogénique à faible tension d'attaque grille-cathode

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