HVPE Growth on MOVPE-Grown Semipolar (112̄2) GaN 75 HVPE Growth on MOVPE-Grown Semipolar (112̄2) GaN

For the GaN material system, one reason for the breaking down of the efficiency is the socalled quantum confined Stark effect (QCSE). Since today’s LEDs are grown in the common [0001] (c-)direction, the internal polarization fields are perpendicular to the quantum wells. The cause of these internal fields are spontaneous and piezoelectric polarization. The reason for the latter is mechanical strain that increases with higher In incorporation in the quantum wells, which is necessary for long-wavelength emission. This leads to a local separation of electrons and holes in the quantum wells. Thus their lifetime increases and the radiative recombination rate decreases. This is discussed to be a major reason for the decrease of the device efficiency [1–3].