Germanium for VCSEL Applications
Main characteristics of Germanium for VCSELs
No dislocations
Umicore Germanium has 0 EPD (etch pitch density), which results in a better yield and long term device reliability. The burn-in of final devices may be reduced.

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