Semiconductor and Device Technology III-V Semiconductors Informational

When should I select GaN over GaAs for a power amplifier design?

Q: Can I use GaN for receiving (LNA)?

GaN LNAs exist but have higher noise figure than GaAs: GaN HEMT NF at 10 GHz: 0.8-1.5 dB. GaAs pHEMT NF at 10 GHz: 0.3-0.5 dB. InP HEMT NF at 10 GHz: 0.2-0.3 dB. The higher NF of GaN is due to: higher electron temperature in the channel (the high-field transport that gives GaN high power also increases the noise temperature). Higher gate leakage current (the wider bandgap helps, but the AlGaN/GaN interface has higher defect density than AlGaAs/GaAs). GaN LNAs are used when: the LNA must survive high power levels (e.g., front-end LNA without a limiter in a radar system). GaN can handle > +30 dBm input power without damage (GaAs pHEMT damages at +20-25 dBm). The NF penalty (0.5-1 dB) is traded for the survivability. This is common in military radar receivers where a jammer may illuminate the antenna with high power.

The choice between GaN and GaAs for a PA depends on the specific requirements of the application: (1) Choose GaN when: high output power is needed (> 5 W per device). GaN has 5-10× higher power density than GaAs (5-12 W/mm gate periphery vs 0.5-1.5 W/mm for GaAs). A single GaN device can deliver the power that would require multiple GaAs devices combined. High voltage operation is needed. GaN has breakdown voltage > 60 V (vs 15-25 V for GaAs). This allows operation at higher drain voltages: V_DD = 28-50 V for GaN vs 5-12 V for GaAs. Higher voltage = simpler power supply design and lower current for the same power. Wideband operation is needed. GaN can maintain high efficiency over wider bandwidths (the high impedance from high voltage operation makes wideband matching easier). A GaN PA at 2 GHz can cover an octave bandwidth (1-2 GHz) with > 50% PAE. Harsh environments (high temperature). GaN on SiC operates at junction temperatures up to 225°C (vs 150-175°C for GaAs). (2) Choose GaAs when: low noise is the priority (LNA design). GaAs pHEMT has lower noise figure than GaN (0.3-0.5 dB at 10 GHz vs 0.8-1.5 dB for GaN). The low-noise performance of GaAs makes it the preferred technology for receiver front ends. Moderate power is sufficient (< 5 W). GaAs PAs in the 0.1-5 W range are mature, low-cost, and widely available. Single supply voltage is acceptable (5-12 V). GaAs PAs work directly from standard supply voltages without requiring high-voltage DC-DC converters. Higher frequency (> 40 GHz). GaAs pHEMT and InP HEMT have higher fT/fmax than current GaN processes, providing more gain at mmWave frequencies. GaN is catching up (GaN HEMT with fT > 200 GHz demonstrated) but GaAs remains the performance leader above 40 GHz for many applications. Cost sensitivity. GaAs processes are more mature and generally cheaper per die area than GaN. For consumer devices (handset PAs, Wi-Fi): GaAs HBT is the standard.

Category: Semiconductor and Device Technology

Updated: April 2026

Product Tie-In: Transistors, MMICs, Evaluation Boards

GaN vs GaAs PA Selection

The GaN vs GaAs decision is one of the most important technology choices in RF PA design. The answer depends on a complex interaction of performance, cost, and system requirements.

Power Density Comparison

(1) GaN HEMT on SiC: power density: 5-12 W/mm at L-band to S-band (1-4 GHz). 3-6 W/mm at X-band (8-12 GHz). 2-4 W/mm at Ka-band (26-40 GHz). This high power density comes from: high breakdown voltage (> 60 V → can swing large voltage across the load), high current density (> 1 A/mm gate periphery), and high saturated electron velocity (2.5 × 10^7 cm/s). (2) GaAs pHEMT: power density: 0.5-1.5 W/mm at L/S-band. 0.5-1.0 W/mm at X-band. 0.3-0.7 W/mm at Ka-band. The lower power density means more gate periphery (more transistor cells) for the same output power. A 100 W PA: GaN: requires approximately 10-20 mm of gate periphery (achievable on a single die). GaAs: requires approximately 100 mm of gate periphery (impractical on a single die; requires power combining of multiple devices). (3) GaAs HBT: used primarily for handset PAs (WCDMA, LTE, 5G sub-6 GHz). Power: 1-5 W per PA IC. Voltage: 3.4-5 V (single Li-ion cell or 5 V supply). Very mature, very low cost. The GaAs HBT is not a direct competitor to GaN (different market: consumer vs infrastructure).

Application Matrix

(1) Cellular base station (sub-6 GHz): GaN is the clear winner. Power levels: 20-100 W per PA. Efficiency requirements: > 50% PAE for thermal management. Wideband: must cover multiple bands (e.g., 1.8-2.7 GHz). GaN with DPD achieves > 50% PAE over these bands. (2) Cellular handset PA: GaAs HBT (dominant, mature, low cost). CMOS PA (emerging for high integration). GaN is not used (the power level is 1-3 W, and the cost and voltage are not competitive). (3) Radar: GaN for transmit PA (high peak power, often pulsed). GaAs pHEMT for receiver LNA (low noise). GaN is replacing traveling-wave tubes (TWTs) in many military radar applications. (4) Satellite communication: GaN for ground terminal HPAs (10-100 W). GaAs for satellite transponder SSPAs (5-20 W, weight-sensitive). GaN for next-generation satellite payloads (emerging). (5) Electronic warfare: GaN for wideband jammers (need 100+ W over multi-octave bandwidth). GaN is the only solid-state technology that can deliver this performance.

Technology Comparison

GaN: V_BR > 60V, P_density 5-12 W/mm
GaAs: V_BR 15-25V, P_density 0.5-1.5 W/mm
GaN PA: V_DD = 28-50V, I_low
GaAs PA: V_DD = 5-12V, I_higher
GaN NF: 0.8-1.5dB, GaAs NF: 0.3-0.5dB

Common Questions

Frequently Asked Questions

Is GaN always more expensive than GaAs?

Currently: yes, for the same die size. GaN on SiC: wafer cost $2,000-$5,000 per 4-inch wafer (the SiC substrate is expensive). GaAs: wafer cost $200-$500 per 6-inch wafer (mature process, high volume). Per mm² of die: GaN is 5-15× more expensive than GaAs. However: GaN power density is 5-10× higher. So the die needed for a given power level is much smaller. Net cost per watt: GaN and GaAs are increasingly comparable for power levels > 5 W. Below 5 W: GaAs is cheaper (the die size is already small, and the GaN cost premium is not offset by the size reduction). Trend: GaN on Si (instead of GaN on SiC) is emerging as a lower-cost alternative. GaN on Si uses standard 8-inch silicon wafers (much cheaper). The thermal performance is worse (Si has 3× lower thermal conductivity than SiC), but for moderate-power applications (< 10 W), GaN on Si may become cost-competitive with GaAs.

Can I use GaN for receiving (LNA)?

GaN LNAs exist but have higher noise figure than GaAs: GaN HEMT NF at 10 GHz: 0.8-1.5 dB. GaAs pHEMT NF at 10 GHz: 0.3-0.5 dB. InP HEMT NF at 10 GHz: 0.2-0.3 dB. The higher NF of GaN is due to: higher electron temperature in the channel (the high-field transport that gives GaN high power also increases the noise temperature). Higher gate leakage current (the wider bandgap helps, but the AlGaN/GaN interface has higher defect density than AlGaAs/GaAs). GaN LNAs are used when: the LNA must survive high power levels (e.g., front-end LNA without a limiter in a radar system). GaN can handle > +30 dBm input power without damage (GaAs pHEMT damages at +20-25 dBm). The NF penalty (0.5-1 dB) is traded for the survivability. This is common in military radar receivers where a jammer may illuminate the antenna with high power.

What about GaN for 5G mmWave base stations?

GaN is increasingly used for 5G mmWave gNB PAs at 28 and 39 GHz: GaN on SiC at 28 GHz: PAE ≈ 25-35% (vs 15-25% for SiGe). P_sat per element: +23 to +28 dBm (vs +15 to +20 dBm for SiGe). The higher PAE reduces the heat load per element, which is critical in a 256-element array. The higher P_sat allows the same EIRP with fewer elements (cost saving). Challenge: cost. GaN at 28 GHz requires fine gate length (100-150 nm) on expensive SiC substrates. The cost per element is higher than SiGe. Trade-off: fewer GaN elements (each with higher power) vs more SiGe elements (each with lower power and lower cost). The optimal choice depends on the total system cost (including thermal management, which is cheaper with higher-efficiency GaN PAs).

Keep Reading