Silicon germanium (Si₍₁₋ₓ₎Ge₍ₓ₎) is a group-IV alloy that is fully miscible across all compositions. Adding germanium to silicon reduces the bandgap (0.66 eV for pure Ge vs 1.12 eV for Si), increases carrier mobility — electron mobility in strained SiGe approaches ~2,000 cm²/V·s — and introduces a compressive biaxial strain when grown epitaxially on silicon substrates. The alloy is uniquely compatible with standard CMOS fabs, which distinguishes it from III-V materials and is the primary source of its commercial traction.
Three device classes dominate. First, SiGe heterojunction bipolar transistors (HBTs) are produced in high-volume BiCMOS processes (IBM, GlobalFoundries, TSMC) and are the standard technology for mmWave and RF front-end circuits: low-noise amplifiers, voltage-controlled oscillators, and phased-array beamformers from 5G sub-6 GHz through 100+ GHz automotive radar bands. Rf Frontend Silicon tracks the investment landscape here; Sige Semiconductor Silanna and Sicoya work in SiGe-based photonic and RF integration. Second, strained SiGe or pure Ge layers are used as the high-mobility channel in advanced CMOS nodes (Ge PMOS); this is a core enabler in sub-3 nm gate stacks. Third, Ge/SiGe quantum wells are a leading platform for silicon-compatible spin qubits, tracked under Topological Qubits (Microsoft Majorana); Hrl Laboratories works on SiGe spin qubit architectures. The Germanium-on-Silicon Mid-IR Photonics concept covers the photonic use of Ge-on-Si for mid-IR waveguides.
The absence of a direct bandgap in Si and Ge limits SiGe to indirect-gap photonics and excludes it from efficient light emission, keeping emitter applications with III-V materials.
Frontier
- Can SiGe HBT nodes keep pace with III-V GaN and InP in mmWave power amplifier performance beyond 100 GHz?
- Will Ge-channel PMOS transistors in SiGe stacks displace III-V channels in sub-3 nm CMOS nodes?
- Does SiGe quantum-well spin-qubit fidelity converge with silicon-only spin qubits, or does residual Ge nuclear spin decoherence remain a fundamental floor?