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

Outline Introduction Introduction Gallium Nitrate Gallium Nitrate AlGaN/GaN HEMT operation principles AlGaN/GaN HEMT operation principles 2 dimensional electron gas 2 dimensional electron gas Origin of 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Charge control Summary Summary References References

Introduction Transistor are used in many electronic devices, e.g. switch, amplifiers, oscillators. Transistor are used in many electronic devices, e.g. switch, 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 AlGaAs/GaAs  AlGaN/GaN. Conventional HEMTs use a AlGaAs/GaAs  AlGaN/GaN.

Introduction Heterojuction  2 DEG 3 contacts: Source and drain  ohmic contacts. Gate  Schottky barrier. Current flows from the source to the drain.

Introduction Output characteristic: Transconductance:

Introduction 1960 GaN small crystals was made GaN small crystals was made Takashi Minura, Fujitsu laboratories designed the features of the first HEMT Takashi Minura, Fujitsu laboratories designed the features of the first HEMT HEMT was announced the lowest noise device HEMT was announced the lowest noise device Kahn demonstrated the first AlGaN/GaN HEMT Kahn demonstrated the first AlGaN/GaN HEMT.

Outline Introduction Introduction Gallium Nitrate Gallium Nitrate AlGaN/GaN HEMT operation principles AlGaN/GaN HEMT operation principles 2 dimensional electron gas 2 dimensional electron gas Origin of 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Charge control Summary Summary References References

Gallium Nitrate High electron density (Polarization effects). High electron density (Polarization effects). Adequate for high power amplifiers  Adequate for high power amplifiers  High breakdown voltage. Large heat capacity. Large heat capacity. Necessary to growth in a wafer of another material. Necessary to growth in a wafer of another material. Molecular Beam Epitaxy. Molecular Beam Epitaxy. Metal Organic Vapor Beam Epitaxy. Metal Organic Vapor Beam Epitaxy.

Gallium Nitrate Substrate material. Substrate material. Sapphire Sapphire o Most used material, cheap, good quality commercial wafers. o Large lattice mismatch  high amount of dislocation. o Poor thermal conductivity. Silicon Carbide. Silicon Carbide. o Low lattice mismatch. o High thermal capacity. o Expensive material. Silicon Silicon o Most common semiconductor. o Acceptable thermal conductivity. o Available in large quantities.

Outline Introduction Introduction Gallium Nitrate Gallium Nitrate AlGaN/GaN HEMT operation principles AlGaN/GaN HEMT operation principles 2 dimensional electron gas 2 dimensional electron gas Origin of 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Charge control Summary Summary References References

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)

Triangular quantum well Triangular quantum well Infinitely high barrier for z 0. Infinitely high barrier for z 0. Applying boundary condition. Applying boundary condition. Airy function Airy function cn  0 of Airy function

Operation principles (Polarization) AlGaN/GaN HEMTs transistor don’t need doping to obtain a high electron density. AlGaN/GaN HEMTs transistor don’t need doping to obtain a high electron density. Spontaneous polarization. + Piezoelectronic polarization. = (cm 2 /Vs) carrier concentration (cm 2 /Vs) carrier 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 (Polarization)

Operation principes (Charge control) Charge density, controlled by a gate voltage. Charge density, controlled by a gate voltage. Schootky barrier. Schootky barrier.

Operation principles (Charge control)

Outline Introduction Introduction Gallium Nitrate Gallium Nitrate AlGaN/GaN HEMT operation principles AlGaN/GaN HEMT operation principles 2 dimensional electron gas 2 dimensional electron gas Origin of 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Charge control Summary Summary References References

Summary HEMT transistor are widely used in electronic application. HEMT transistor are widely used in electronic application. AlGaN/GaN structure looks promising. AlGaN/GaN structure looks promising. Still in research. Still in research. Electron transistor. Electron transistor.

Outline Introduction Introduction Gallium Nitrate Gallium Nitrate AlGaN/GaN HEMT operation principles AlGaN/GaN HEMT operation principles 2 dimensional electron gas 2 dimensional electron gas Origin of 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Charge control Summary Summary References References

References “Crecimiento y fabricación de transistores HEMT de AlGaN/GaN por epitaxia de haces moleculares.” Tesis Doctoral, Ana Jiménez Martín. “Crecimiento y fabricación de transistores HEMT de AlGaN/GaN por epitaxia de haces moleculares.” Tesis Doctoral, Ana Jiménez Martín. “The physics of low dimensional semiconductors.” John H. Davies. “The physics of low dimensional semiconductors.” John H. Davies. “Characterization of advanced AlGaN HEMT structures” Anders Lundskog. “Characterization of advanced AlGaN HEMT structures” Anders Lundskog. “The physics and chemistry of Solids” Stephen Elliot. “The physics and chemistry of Solids” Stephen Elliot. “GaN based power high electron mobility transistor” Shreepad Karmalkar. “GaN based power high electron mobility transistor” Shreepad Karmalkar. “Power-Supported Bridges for Multi Finger AlGaN/GaN Heterojunciton Field Effect Transistor (HFET)” Michael H.Willemann “Power-Supported Bridges for Multi Finger AlGaN/GaN Heterojunciton Field Effect Transistor (HFET)” Michael H.Willemann

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