Reactor dependent starting transients of doping profiles in MOVPE grown GaN

The quality of heterostructures greatly depends on the accurate placement of dopants. However, doping transients remain as drawback in vapor-phase epitaxy. In this work starting transients of doping profiles of Si and Mg in GaN layers grown by low pressure metal-organic vapor-phase epitaxy (MOVPE) on sapphire have been investigated. Here we restrict the investigation to concentrations typically used for electrical or electro-optical devices which are in the range of 2x1017 cm-3 to 1x1019 cm-3 for Si and 3x1019 cm-3 to 1x1020 cm-3 for Mg. In the case of Mg possible diffusion was excluded by growing the doped layers at a lower growth temperature, far too low for device structures, where the profiles show essentially no sign of Mg back-diffusion. In the case of lower Si concentrations we did not observe diffusion at usual growth temperatures. The profiles were measured by secondary ion mass spectrometry. By comparing the transients from two different reactor types we show and quantitatively explain the influence of adsorption at the internal surfaces of the reactor on the dopant incorporation.