HEMT
Understanding HEMT Technology
HEMTs are the workhorses of modern microwave electronics. The 2DEG at the heterojunction provides electrons with mobilities 5-10x higher than bulk silicon, enabling operation at frequencies up to 300+ GHz. GaAs pHEMT dominates for low-noise applications; GaN HEMT dominates for high-power.
HEMT Variants
- GaAs pHEMT: NF < 0.5 dB at 10 GHz. Standard for LNAs and receive MMICs to 100 GHz.
- GaN HEMT: High power (5-10 W/mm). Standard for PAs from 1-40 GHz.
- InP HEMT: Lowest noise at mmWave/sub-mmWave (NF < 1 dB at 100 GHz). Used in radio astronomy and deep-space receivers.
- mHEMT (metamorphic): InP-like performance on GaAs substrate. Lower cost alternative to InP.
GaAs pHEMT: fT = 100-200 GHz, fmax = 150-300 GHz
GaN HEMT: fT = 30-100 GHz, fmax = 100-300 GHz
InP HEMT: fT = 300-700 GHz, fmax = 500-1000 GHz
GaAs pHEMT noise figure:
1 GHz: 0.3 dB
10 GHz: 0.5 dB
40 GHz: 1.0 dB
94 GHz: 2.0 dB
Frequently Asked Questions
What is a HEMT?
A HEMT uses a heterojunction between different semiconductors to create a sheet of electrons with very high mobility. This enables the highest frequency operation, lowest noise, and highest gain of any transistor type. GaAs pHEMT and GaN HEMT are the dominant RF transistor technologies.
What is the difference between GaAs and GaN HEMTs?
GaAs pHEMTs have the lowest noise figure and are used for LNAs and receive circuits. GaN HEMTs have the highest power density and breakdown voltage, used for power amplifiers. GaAs dominates receive; GaN dominates transmit.
What is the 2DEG?
The 2DEG (two-dimensional electron gas) is a thin sheet of electrons confined at the heterojunction interface. Electrons in the 2DEG have very high mobility because they are separated from the ionized donor atoms, reducing scattering. This is the key to HEMT's high-frequency performance.