We present a study on the dependence of the external Quantum Efficiency (QE) of Light Emitting Diodes (LEDs) on the device properties and p-contact metallisation. The external QE could be doubled by changing the p-type contact from oxidised Ni/Au to non-annealed Ag. The best value for the external QE of an unpackaged device is 13.5% and is obtained when the reflection from the Ag mirror contact is in phase with the QW emission.