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Chapter IIIChapter IIISemiconductor DevicesSemiconductor Devices

半導體元件

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Basic Building Blocks of Semiconductor DevicesBasic Building Blocks of Semiconductor Devices

(a) M-S Junction (b) P-N Junction (c) Heterojuction (d) MOS structure

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Metal-Semiconductor ContactMetal-Semiconductor Contact

• Schottky contact– Rectifying contact– Schottky Barrier– M-S devices– Unipolar devices– High-speed devices

• Ohmic contact– Non-rectifying contact– Specific contact resistance– The apace charge width in a M-S

contact is inversely proportional to the square root of the semiconductor doping.The probability of tunneling through the barrier increases with the increasing doping concentration.

– ElectrodesEnergy-band diagram of a heavily doped n-

semiconductor-to-metal junction

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Schottky-Barrier DiodeSchottky-Barrier Diode

• M-S junction device

• Unipolar device

• Majority-carrier device

• Without minority- carrier-storage effect

• III-V compound semiconductors (GaAs)

• Properities of devices:– High operation speed

– Lower cut-in voltage

– Higher saturation current

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The P-N Diode --- Under Thermal EquilibriumThe P-N Diode --- Under Thermal Equilibrium

P-type and N-type semiconductors before and after the junction formed

A p-n junction with abrupt doping charges at the metallurgical junction

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The P-N Diode --- Under Biasing ConditionsThe P-N Diode --- Under Biasing Conditions

(a) Thermal equilibrium

(b) Forward-bias condition.

(c) Reverse-bias condition

Current-voltage characteristics of a typical Si p-n junction

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Classification of Semiconductor DevicesClassification of Semiconductor Devices

• Bipolar Devices– P-N Junction Diode

– Bipolar Junction Transistor (BJT)

– Heterojunction Bipolar Transistor (HBT)

– Thyristor and related power devices

• Unipolar Devices– Schottky-barrier diode (SBD)

– Junction Field Effect Transistor (JFET)

– Metal-Oxide-Semiconductor FET (MOSFET)

– MOS Diode (Capacitor)

– Complementary MOS (CMOS) BiMOS and BiCMOS

– Power MOS

• High-Speed Devices– Metal-Semiconductor FET (MESFET)

– Modulation-Doped FET (MODFET), High-Electron-Mobility Transistor (HEMT)

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Semiconductor Devices (continued)Semiconductor Devices (continued)

• Microwave Devices– Tunnel diode

– IMPATT diode

– Transferred-Electron Device (TED)

– Quantum-Effect Devices

– Hot-Electron Devices

• Photonic Devices– Light Emitting Diode (LED)

– Semiconductor Laser (Laser Diode, LD)

– Photodetector• Photodiode (PD), Avalanche Photodiode (APD)

• Phototransistor (PT)

– Solar Cell

– Display Devices• Thin-Film Transistor LCD (TFT-LCD)

• Organic Electroluminescence Display (OELD) or Organic Light Emitting Diode (OLED)

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Semiconductor Devices (continued)Semiconductor Devices (continued)

• Integrated Devices– Passive Components

• IC Resistor, IC Capacitor, IC Inductor

– MOS Menory• Dynamic Random Access Memory (DRAM)

• Static Random Access Memory (SRAM)

• Nonvolatile Memory

• Erasable-Programmable Read-Only Memory (EPROM)

• Electrically Erasable-Programmable Read-Only Memory (EEPROM)

• Flash Memory

• Single-Electron Memory

• MEMS devices

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The Bipolar Junction Transistor (BJT)The Bipolar Junction Transistor (BJT)

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The MOSFETThe MOSFET

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The CMOSThe CMOS

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MESFETMESFET

Ohmic ContactSchottky Contact

Mesa StructureTo minimize parasitic

capacitances

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MODFETMODFET

• Modulation Doped FET– A thin undoped well bounded by

two wider bandgap doped barrier

• HFET (Heterojunction FET)

• 2DEG FET or TEGFET,

• SEDFET (Separately Doped FET)

• Advantages:– Extremely high cutoff frequency

and fast access time

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HEMTHEMT

• HEMT: – High Electron Mobility Transistor– 250,000 cm2/V-s at 77K– 2,000,000 cm2/V-s at 4K

• Why HEMT?– In conventional MESFET: Channel doping carrier number But mobility (impurity scattering) conductivity is limited ( = q n )

– For HEMT: Sheet carrier density is as high as

1012 cm-2 (~1020cm-3 for 10-nm thick channel layer)