HBT vs HEMT: Key Differences Explained

This article compares HBT (Heterojunction Bipolar Transistor) and HEMT (High Electron Mobility Transistor), highlighting the key differences between these two types of transistors.

HBT - Heterojunction Bipolar Transistor

• 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

• 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