The mobility differences in flow exists due to the apparent differences in mass.
Recombination is not essential for semiconductor flow.
In fact, minimizing recomb. allows many of the best unique products to emerge. e.g. Ultra-high purity materials, permit high voltage IGBT's, high-speed microwave components, quantum dots and nanowires by design, special materials ( GaAs, GaN, InP) all benefit from low recombination rates.
Generally, lower voltage breakdown is always caused by material impurities which may have other benefits. .e.g. Base-emitter junctions and LEDs are typically -5V max before breakdown occurs.