(AlGaN/GaN) High electron mobility transistors Low dimensional System Master of Nanoscience Olatz Idigoras Lertxundi

(AlGaN/GaN)(AlGaN/GaN)High electron mobility High electron mobility

transistorstransistors

Low dimensional SystemLow dimensional System

Master of NanoscienceMaster of NanoscienceOlatz Idigoras LertxundiOlatz Idigoras Lertxundi

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• IntroductionIntroduction• Gallium NitrateGallium Nitrate• AlGaN/GaN HEMT operation principlesAlGaN/GaN HEMT operation principles

2 dimensional electron gas2 dimensional electron gas Origin of 2 dimensional electron gasOrigin of 2 dimensional electron gas Charge controlCharge control

• SummarySummary• ReferencesReferences

IntroductionIntroduction

• Transistor are used in many Transistor are used in many electronic devices, e.g. switch, electronic devices, e.g. switch, amplifiers, oscillators.amplifiers, oscillators.

• To satisfy growing demands of:To satisfy growing demands of: High power.High power. High speed. High speed. High efficiency communications.High efficiency communications.

• Heterostructure field effect device.Heterostructure field effect device.• Conventional HEMTs use a Conventional HEMTs use a

AlGaAs/GaAsAlGaAs/GaAs AlGaN/GaN. AlGaN/GaN.


• Heterojuction 2 DEG

• 3 contacts: Source and drain

ohmic contacts. Gate Schottky

barrier.• Current flows from

the source to the drain.


tconsVDSGS

DS

V

Igm

tan

• Output characteristic:

• Transconductance:


• 1960 GaN small crystals was made.1960 GaN small crystals was made.• 1980 Takashi Minura, Fujitsu 1980 Takashi Minura, Fujitsu

laboratories designed the features of laboratories designed the features of the first HEMT.the first HEMT.

• 1985 HEMT was announced the 1985 HEMT was announced the lowest noise device.lowest noise device.

• 1994 Kahn demonstrated the first 1994 Kahn demonstrated the first AlGaN/GaN HEMT.AlGaN/GaN HEMT.

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Gallium NitrateGallium Nitrate

• High electron density (Polarization High electron density (Polarization effects).effects).

• Adequate for high power amplifiersAdequate for high power amplifiersHigh breakdown voltage.High breakdown voltage.

• Large heat capacity.Large heat capacity.• Necessary to growth in a wafer of Necessary to growth in a wafer of

another material.another material. Molecular Beam Epitaxy.Molecular Beam Epitaxy. Metal Organic Vapor Beam Epitaxy.Metal Organic Vapor Beam Epitaxy.

Gallium NitrateGallium Nitrate

• Substrate material.Substrate material. SapphireSapphire

o Most used material, cheap, good quality commercial Most used material, cheap, good quality commercial wafers.wafers.

o Large lattice mismatch Large lattice mismatch high amount of dislocation. high amount of dislocation.o Poor thermal conductivity.Poor thermal conductivity.

Silicon Carbide.Silicon Carbide.o Low lattice mismatch.Low lattice mismatch.o High thermal capacity.High thermal capacity.o Expensive material.Expensive material.

SiliconSilicono Most common semiconductor.Most common semiconductor.o Acceptable thermal conductivity.Acceptable thermal conductivity.o Available in large quantities.Available in large quantities.

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• Discontinuity through the conduction band of the two semiconductors determines a charge transfer, creating a triangular potential.

• Electrons are confined in the triangular potential in discrete quantum state.

• Mobility of the electrons in 2DEG is higher than in a bulk.

Operation principles (2 DEG)Operation principles (2 DEG)

Operation principles (2 DEG)Operation principles (2 DEG)

• Triangular quantum wellTriangular quantum well Infinitely high barrier for z<0 with a linear Infinitely high barrier for z<0 with a linear

potential V(z)=eFz for z>0.potential V(z)=eFz for z>0.

Applying boundary condition.Applying boundary condition. Airy functionAiry function

cncn 0 of Airy function 0 of Airy function

)()(2 2

22

zzeFzdz

d

m

h

)3/1(2

]2

)([

m

eFcnn

)()(0

eFzAizn

Operation principles Operation principles (Polarization)(Polarization)

• AlGaN/GaN HEMTs transistor don’t need AlGaN/GaN HEMTs transistor don’t need doping to obtain a high electron density.doping to obtain a high electron density.

Spontaneous polarization.Spontaneous polarization.++

Piezoelectronic polarization.Piezoelectronic polarization. ==

101013 13 (cm (cm22/Vs) carrier /Vs) carrier concentration concentration

• Spontaneous polarization. Wurtzite structure. Polarization at zero strain. Due to the lack of symmetry. It appears in both layers.

• Piezoelectronic polarization. Difference of the lattice constant of GaN

and AlGaN. Pseudomorfic growth of AlGaN.

Operation principles Operation principles (Polarization)(Polarization)

Operation principes (Charge Operation principes (Charge control)control)

• Charge density, controlled by a gate Charge density, controlled by a gate voltage.voltage.

• Schootky barrier.Schootky barrier.

Operation principles (Charge Operation principles (Charge control)control)

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SummarySummary

• HEMT transistor are widely used in HEMT transistor are widely used in electronic application.electronic application.

• AlGaN/GaN structure looks promising.AlGaN/GaN structure looks promising.

• Still in research.Still in research.

• Electron transistor. Electron transistor.

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ReferencesReferences

• ““Crecimiento y fabricación de transistores HEMT Crecimiento y fabricación de transistores HEMT de AlGaN/GaN por epitaxia de haces moleculares.” de AlGaN/GaN por epitaxia de haces moleculares.” Tesis Doctoral, Ana Jiménez Martín. Tesis Doctoral, Ana Jiménez Martín.

• ““The physics of low dimensional semiconductors.” The physics of low dimensional semiconductors.” John H. Davies.John H. Davies.

• ““Characterization of advanced AlGaN HEMT Characterization of advanced AlGaN HEMT structures”structures” Anders Lundskog. Anders Lundskog.

• ““The physics and chemistry of Solids”The physics and chemistry of Solids” Stephen Stephen Elliot.Elliot.

• ““GaN based power high electron mobility GaN based power high electron mobility transistor”transistor” Shreepad Karmalkar. Shreepad Karmalkar.

• ““Power-Supported Bridges for Multi Finger Power-Supported Bridges for Multi Finger AlGaN/GaN Heterojunciton Field Effect Transistor AlGaN/GaN Heterojunciton Field Effect Transistor (HFET)” Michael H.Willemann(HFET)” Michael H.Willemann

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(AlGaN/GaN) High electron mobility transistors Low dimensional System Master of Nanoscience Olatz Idigoras Lertxundi