Germanium for VCSEL Applications

Main characteristics of Germanium for VCSELs

Germanium compared to Silicon and GaAs

Property

Silicon

GaAs

Germanium

Crystal Structure Diamond Zincblende Diamond Si and Ge are elemental semiconductors with similar large (12") diameter 0 EPD* cyrstal processes
Density (g/cm³) 2.33 5.32 5.33
Lattice constant (Å) 5.430 5.653 5.658 Ge and GaAs are lattice matched
Bandgap energy at 300K (eV) 1.12 1.42 0.66
Electron mobility (cm²/V-s) 1350 8500 3900 Ge has both high electron and hole mobility
Hole mobility (cm²/V-s) 480 400 1900
Melting point (°C) 1415 1238 937
Thermal expansion (1/°C) 2.6 10-6 5.7 10-6 5.9 10-6 Ge and GaAs have similar thermal expansion
Thermal conductivity (W/cm°C) 1.3 0.55 0.55
Fracture thoughness (MPa.m1/2) 0.8 0.31 0.66 - 0.72 Ge is twice as tough as GaAs

* EPD: Etch pitch density, dislocation density