Al Ga NGa N High electron mobility transistors
(Al. Ga. N/Ga. N) High electron mobility transistors Low dimensional System Master of Nanoscience Olatz Idigoras Lertxundi
Outline • • • Introduction Gallium Nitrate Al. Ga. N/Ga. N HEMT operation principles • • 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Summary References
Introduction • • Transistor are used in many electronic devices, e. g. switch, amplifiers, oscillators. To satisfy growing demands of: High power. High speed. High efficiency communications. • • Heterostructure field effect device. Conventional HEMTs use a Al. Ga. As/Ga. As Al. Ga. N/Ga. N.
Introduction • • Heterojuction 2 DEG 3 contacts: Source and drain ohmic contacts. Gate Schottky barrier. • Current flows from the source to the drain.
Introduction • • Transconductance: Output characteristic:
Introduction • • 1960 Ga. N small crystals was made. 1980 Takashi Minura, Fujitsu laboratories designed the features of the first HEMT. 1985 HEMT was announced the lowest noise device. 1994 Kahn demonstrated the first Al. Ga. N/Ga. N HEMT.
Outline • • • Introduction Gallium Nitrate Al. Ga. N/Ga. N HEMT operation principles • • 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Summary References
Gallium Nitrate • • High electron density (Polarization effects). Adequate for high power amplifiers High breakdown voltage. Large heat capacity. Necessary to growth in a wafer of another material. Molecular Beam Epitaxy. Metal Organic Vapor Beam Epitaxy.
Gallium Nitrate • Substrate material. Sapphire o o o Silicon Carbide. o o o Most used material, cheap, good quality commercial wafers. Large lattice mismatch high amount of dislocation. Poor thermal conductivity. Low lattice mismatch. High thermal capacity. Expensive material. Silicon o o o Most common semiconductor. Acceptable thermal conductivity. Available in large quantities.
Outline • • • Introduction Gallium Nitrate Al. Ga. N/Ga. N HEMT operation principles • • 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Summary References
Operation principles (2 DEG) • • • 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 2 DEG is higher than in a bulk.
Operation principles (2 DEG) • Triangular quantum well Infinitely high barrier for z<0 with a linear potential V(z)=e. Fz for z>0. Applying boundary condition. Airy function cn 0 of Airy function
Operation principles (Polarization) • Al. Ga. N/Ga. N HEMTs transistor don’t need doping to obtain a high electron density. Spontaneous Piezoelectronic polarization. Spontaneous polarization. Wurtzite Difference structure. of the lattice constant of Ga. N and + Al. Ga. N. Polarization at zero strain. Piezoelectronic polarization. Due Pseudomorfic of Al. Ga. N. to the lackgrowth of symmetry. = It appears in both layers. 1013 (cm 2/Vs) carrier concentration •
Operation principles (Polarization)
Operation principes (Charge control) • • Charge density, controlled by a gate voltage. Schootky barrier.
Operation principles (Charge control)
Outline • • • Introduction Gallium Nitrate Al. Ga. N/Ga. N HEMT operation principles • • 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Summary References
Summary • HEMT transistor are widely used in electronic application. • Al. Ga. N/Ga. N structure looks promising. • Still in research. • Electron transistor.
Outline • • • Introduction Gallium Nitrate Al. Ga. N/Ga. N HEMT operation principles • • 2 dimensional electron gas Origin of 2 dimensional electron gas Charge control Summary References
References • “Crecimiento y fabricación de transistores HEMT de Al. Ga. N/Ga. N por epitaxia de haces moleculares. ” Tesis Doctoral, Ana Jiménez Martín. • • • “The physics of low dimensional semiconductors. ” John H. Davies. “Characterization of advanced Al. Ga. N HEMT structures” Anders Lundskog. “The physics and chemistry of Solids” Stephen Elliot. “Ga. N based power high electron mobility transistor” Shreepad Karmalkar. “Power-Supported Bridges for Multi Finger Al. Ga. N/Ga. N Heterojunciton Field Effect Transistor (HFET)” Michael H. Willemann
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