We report on the growth of InAlGaP-layers and the fabrication of red microcavity LEDs (MCLEDs) on germanium (Ge) substrates. High-quality InAlGaP-layers have been grown on 3" Ge-substrates with excellent uniformity on photoluminescence wavelength and intensity. InAlGaP MCLEDs with an Al0.55Ga0.45As current spreading layer and 200 mum device diameter, emitting at 650 nm exhibit a maximum quantum efficiency of 4.35% at 10 mA and a maximum optical power of 5 mW at 80 mA. MCLEDs emitting at 638 nm exhibit a maximum quantum efficiency of 4% at 10 mA and an optical power of 5 mW at 100 mA. GaP as an alternative current spreading layer is also investigated.