INFLUENCE OF SUBSTRATE ELECTRICAL BIAS ON THE GROWTH OF GAN IN PLASMA-ASSISTED EPITAXY

A sample bias on the order of - 15 V arises during electron cyclotron resonance plasma-assisted epitaxy of GaN on insulating substrates. In contrast, conducting substrates enable growth under zero or positive bias conditions. Surface morphology of GaN/Si(111) is progressively smoother with increasing bias (-10 to + 10 V) for a microwave power of 30 W. Emission spectroscopy of the plasma suggests that both N and N2+ are produced from collisions involving N2* and that for low power (10 W), the N and N2+ production is limited by the N2* abundance. In contrast, at higher power (50 W), ion and atom production appears limited by the electron collision frequency. Electrostatic probe measurements near the growth stage indicate that the ion energy has a minimum of about 6 eV, attained at low plasma power or at medium power (30 W) with a positive substrate bias. Mg-doped films produced at 10 W and zero bias are highly resistive. p-n junction diodes formed by Si-doped GaN grown on Mg-doped GaN on p-type Si are operated at relatively low current densities of 100 A cm-2 and emit light near 2.5 eV at room temperature.