gan on silicon
**GaN-on-Silicon Power Semiconductors** are the **gallium nitride high-electron-mobility transistors (HEMTs) grown on silicon wafers that enable switching power supplies and RF amplifiers with dramatically higher efficiency and frequency than silicon alternatives** — exploiting GaN's wide bandgap (3.4 eV vs Si 1.1 eV), high breakdown field (3.3 MV/cm), and inherent two-dimensional electron gas (2DEG) to achieve fast switching at high voltages with low on-resistance, enabling smaller, lighter power conversion systems.
**GaN Material Advantages vs Silicon**
| Property | Silicon | GaN | SiC |
|----------|---------|-----|-----|
| Bandgap (eV) | 1.1 | 3.4 | 3.3 |
| Breakdown field (MV/cm) | 0.3 | 3.3 | 2.5 |
| Electron mobility (cm²/V·s) | 1400 | 2000 (2DEG) | 950 |
| Thermal conductivity (W/m·K) | 150 | 130 | 370 |
| Switching frequency | Low | Very High | High |
**2DEG (Two-Dimensional Electron Gas)**
- GaN HEMT structure: AlGaN/GaN heterojunction.
- Spontaneous and piezoelectric polarization at AlGaN/GaN interface → electrons accumulate without doping.
- 2DEG: Sheet of electrons confined at interface → very high mobility (≈2000 cm²/V·s) → low resistance.
- Key advantage: No ionized impurity scattering (undoped channel) → high electron mobility.
- Result: Very low on-resistance R_on despite operating at high voltages.
**GaN-on-Si Manufacturing**
- Grown on 6-inch or 8-inch silicon wafers → leverages existing Si fab equipment (MOCVD epi on Si).
- Buffer layer challenge: GaN lattice constant 17% larger than Si → buffer strain management layers (AlN, AlGaN graded) to prevent cracking.
- MOCVD (Metal-Organic CVD) growth: TMGa + NH₃ at 1000°C → GaN; TMAl + NH₃ → AlN; ≥2 µm total buffer.
- 8-inch GaN-on-Si: Enables high-volume, low-cost production in standard Si fabs.
**Normally-off (E-mode) vs Normally-on (D-mode)**
- Natural 2DEG is always present → naturally normally-on (depletion mode, D-mode).
- For power electronics: Normally-off (enhancement mode, E-mode) preferred for safety.
- E-mode approaches:
- p-GaN gate: p-type GaN layer raises threshold voltage above 0V.
- Cascode with Si MOSFET: D-mode GaN + Si MOSFET in series → normally-off behavior.
- Recessed gate: Thin AlGaN under gate → 2DEG depleted at zero bias.
**Applications**
- **EV onboard charger**: GaN enables 6.6–22kW charger at < 1L volume; 98% efficiency.
- **Laptop/phone adapter**: GaN chargers 2× smaller than Si chargers at same power.
- **Data center power**: 48V bus converters with GaN → 97%+ efficiency → lower cooling cost.
- **5G base station**: GaN RF power amplifiers at 28 GHz, 5G mmWave.
- **Lidar (autonomous vehicles)**: GaN enables high-repetition-rate pulsed laser drivers.
**Key Players**
- Infineon (OptiMOS GaN), Texas Instruments, ON Semiconductor: Discrete power GaN.
- Navitas Semiconductor: GaN ICs with integrated gate driver (GaNFast).
- Transphorm: GaN-on-SiC for high-reliability applications.
- TSMC: GaN PDK on 8-inch Si wafers for foundry customers.
**GaN vs SiC Trade-offs**
- GaN: Superior switching speed (10–100 MHz), lower cost (Si substrate), < 900V typically.
- SiC: Better thermal (370 W/m·K), reliable at 1700V+, preferred for traction inverters in EVs.
- GaN: Wins at < 650V, high-frequency applications. SiC: Wins at > 900V, high-temperature.
GaN-on-silicon power semiconductors are **the enabling technology for the miniaturization of power conversion in the electrification era** — by switching 5–10× faster than silicon MOSFETs with lower switching losses, GaN allows power supply designers to increase switching frequency from 100 kHz to 1–10 MHz, shrinking magnetic component sizes by 100× and enabling chargers that fit in a shirt pocket at the same wattage that previously required a brick-sized adapter, while their growing adoption in EV onboard chargers and data center power supplies represents a multi-billion-dollar displacement of silicon in power electronics.