Why is GaN better than GaAs for high-power RF?

GaN's advantages come from its wide bandgap (3.4 eV vs. 1.42 eV for GaAs): (1) Higher breakdown voltage: GaN supports 65-100V drain bias vs. 12-15V for GaAs. P = V^2/R, so higher voltage means more power from the same impedance. (2) Higher power density: 5-10 W/mm vs. 1-2 W/mm for GaAs. A 10mm GaN device produces 50-100W; a 10mm GaAs device produces 10-20W. (3) Higher impedance: higher operating voltage means higher optimal load impedance, making matching networks easier and more broadband. (4) Better thermal: on SiC substrate, thermal conductivity is 4.9 W/cm-K vs. 0.46 for GaAs. Less junction temperature rise. GaN's main disadvantages: higher cost (especially on SiC), higher 1/f noise (worse close-in phase noise for oscillators), and more complex bias requirements.

What is GaN on SiC vs. GaN on Si?

GaN on SiC: GaN epitaxy grown on silicon carbide substrate. SiC has excellent thermal conductivity (4.9 W/cm-K), allowing efficient heat extraction. This is the dominant technology for high-power applications: 5G base station PAs, radar, EW, satellite. Foundries: Wolfspeed, Qorvo, MACOM, WIN Semiconductors. Cost: high (SiC substrates are expensive). GaN on Si: GaN epitaxy on standard silicon substrates. Much lower cost because of existing Si infrastructure and larger wafer sizes (200mm vs. 100mm). Thermal conductivity is worse (1.5 W/cm-K). Used for lower-power applications: 5G small cells, Wi-Fi, cable infrastructure. Foundries: TSMC, GlobalFoundries. GaN on Si is closing the performance gap and is expected to dominate consumer and cost-sensitive markets.

Where is GaN used in 5G?

5G Massive MIMO base stations are the largest GaN market by volume. A 64T64R massive MIMO radio contains 64 PA channels, each requiring 5-10W output power at 3.5 GHz (n77/n78). GaN on SiC Doherty PAs achieve 40-50% average efficiency at these power levels. Each radio contains approximately $200-400 of GaN content. With millions of 5G base stations deployed globally, this represents a multi-billion dollar market. GaN is also used in 5G mmWave base stations at 28/39 GHz, though at lower power levels (1-5W per element). For 5G small cells, GaN on Si is increasingly used at 2-5W per channel. In satellite communications, GaN is replacing TWTAs in many applications, offering solid-state reliability at Ka-band and higher.

Semiconductor Technology

Gallium Nitride (GaN)

/gal-ee-um ny-tryd/ (GaN)

GaN is a wide-bandgap semiconductor (E_g = 3.4 eV) enabling 5-10 W/mm power density at 28-65V drain bias, to 100+ GHz. GaN on SiC: highest power/thermal performance for 5G base stations, radar, EW. GaN on Si: lower cost for small cells and consumer. 2DEG mobility: 2000 cm²/V-s. Breakdown: 3.3 MV/cm. The dominant high-power RF technology.

Bandgap: 3.4 eV

Power: 5-10 W/mm

V_DS: 28-65V

Understanding GaN

GaN has transformed the RF power amplifier industry. Its wide bandgap enables higher voltage operation (65V vs. 12V for GaAs), which means higher power from smaller devices. A single GaN transistor can replace multiple GaAs devices in a combined PA. The high power density reduces matching network complexity because the optimal impedance is higher and closer to 50 ohms. On SiC substrates, the excellent thermal conductivity keeps junction temperatures manageable even at extreme power densities.

GaN Material Properties

GaN material properties:
E_g = 3.4 eV (wide bandgap)
E_BR = 3.3 MV/cm (10× Si)
v_sat = 2.5×10⁷ cm/s (2.5× Si)

Johnson FOM:
JM ∝ E_BR×v_sat (GaN = 27× Si)

Power density:
GaN HEMT: 5–10 W/mm @10 GHz
Si LDMOS: 1–2 W/mm @2 GHz

RF Semiconductor Technology Comparison

Technology	Power Density	V_DS	f_max	NF (typical)	Application
GaN on SiC	5-10 W/mm	28-65V	100+ GHz	0.5-2 dB	5G BS, radar, EW
GaN on Si	3-5 W/mm	28-48V	40 GHz	1-3 dB	Small cell, Wi-Fi
GaAs pHEMT	0.8-1.5 W/mm	5-12V	200 GHz	0.3-1 dB	LNA, phone PA
LDMOS	1-2 W/mm	28-50V	3.5 GHz	Not used	Sub-3 GHz BS
InP HEMT	0.3-0.5 W/mm	1-3V	700 GHz	0.1-0.5 dB	mmWave LNA, THz

Key Equations

Noise Figure cascade (Friis):
NF_total = NF₁ + (NF₂−1)/G₁ + (NF₃−1)/(G₁G₂)

Gain (dB):
G = 10log(P_out/P_in) = 20log(V_out/V_in)

IP3 & dynamic range:
SFDR = 2/3(IIP3 − NF − 10log(kTB)) dB

Comparison

Property	GaN	SiC	GaAs	Si
E_g (eV)	3.4	3.26	1.42	1.12
E_BR (MV/cm)	3.3	2.0	0.4	0.3
v_sat (10⁷ cm/s)	2.5	2.0	1.0	1.0
Power density	5–10 W/mm	1–5 W/mm	0.5–1 W/mm	0.2–0.5 W/mm
Thermal (κ)	1.3 W/cmK	4.9 W/cmK	0.46	1.5 W/cmK

Common Questions

Frequently Asked Questions

GaN vs. GaAs?

GaN: 5-10 W/mm, 65V, higher impedance, easier matching. GaAs: 1-2 W/mm, 12V, lower NF, better 1/f noise. GaN for power; GaAs for LNAs and low-noise applications. Cost: GaN on SiC is more expensive.

GaN on SiC vs. Si?

SiC: best thermal (4.9 W/cm-K), highest power, most expensive. Si: 3x worse thermal but 3-5x lower cost, adequate for <5W. SiC for base stations and radar. Si for small cells, consumer, and cable.

5G market?

64T64R massive MIMO: 64 GaN PA channels per radio. $200-400 GaN content per radio. Multi-billion dollar market. Also mmWave 28/39 GHz base stations and satellite Ka-band. GaN is the enabling technology for 5G infrastructure.

Related Terms

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