Terminology » HBT vs HEMT: Difference Between HBT and HEMT

HBT vs HEMT: Difference Between HBT and HEMT

transistor hbt hemt rf semiconductor

Introduction : Heterojunction Bipolar Transistors (HBTs) and High Electron Mobility Transistors (HEMTs) are widely used in high frequency and microwave applications. Although both offer excellent performance, their structures, operating principles, and applications differ significantly. Choosing the right device depends on speed, power and frequency requirements.

HBT - Heterojunction Bipolar Transistor

HBT structure

  • Full Form: Heterojunction Bipolar Transistor

  • Construction: An HBT is a type of BJT (Bipolar Junction Transistor) that uses different semiconductor materials for the Base and Emitter regions. This creates a heterojunction. Figure 1 (above) illustrates the internal structure of an HBT.

  • Materials: HBTs are typically made using materials like InP (Indium Phosphide) or InGaAs (Indium Gallium Arsenide).

  • Performance: HBTs are capable of handling high-frequency signals, often in the range of several 100 GHz.

  • Applications:

    • Fast switching RF circuits
    • High power efficient devices, such as Power Amplifiers (PAs) used in mobile phones.
    • Monolithic optical ICs (Integrated Circuits), such as PIN-based photo detectors.

HEMT - High Electron Mobility Transistor

HEMT structure

  • Full Form: High Electron Mobility Transistor

  • Construction: Figure 2 (above) shows the internal structure of a HEMT. It is a type of FET (Field-Effect Transistor) that incorporates a junction between materials with different band gaps (i.e., a heterojunction). Instead of using doped regions like in MOSFET designs, HEMTs use band gaps as channels.

  • Materials: HEMTs often utilize materials such as GaAs (Gallium Arsenide), AlGaAs (Aluminum Gallium Arsenide), and InGaAs.

  • Applications:

    • HEMTs are typically used at very high frequencies, such as millimeter-wave bands.
    • ON-OFF digital switches
    • Low power amplifiers
    • Satellite receivers

  • Advantages:

    • Higher Gain
    • Higher Switching Speed
    • Low Noise

Difference Between HBT and HEMT

Following table mentions compatison between HBT and HEMT devices.

ParameterHBTHEMT
Device TypeBipolar Junction DeviceField Effect Transistor
Carrier TypeBoth electrons and holesMajority Carriers (Electrons only)
Control MechanismCurrent Controlled DeviceVoltage Controlled Device
Junction TypeHeterojunction between emitter and baseHeterojunction forming 2D electron gas
Operating PrincipleCurrent amplification via carrier injectionChannel conductivity controlled by gate voltage
Input ImpedanceLow to ModerateVery High
Switching SpeedVery HighExtremely High
Transit FrequencyHigh (100 to 500 GHz)Very High (can exceed 500 GHz)
Noise performanceModerateExcellent (low noise)
Power handlingHighModerate
LinearityExcellentGood
Power handlingHighModerate
Typical materialsGaAs, SiGe, InPGaAs, InP, GaN
Breakdown voltageLowerHigher, especially GaN HEMT

Summary: This page provides a clear comparison between HBT and HEMT technologies, covering construction, carrier transport, gain and typical use cases. The explanation helps readers understand which transistor is more suitable for RF amplifiers, microwave ICs and high speed communication systems.