Scanning capacitance microscopy as a tool for the assessment of unintentional doping in GaN

Scanning capacitance microscopy (SCM) is a technique based on atomic force microscopy which provides information about the concentration and distribution of charge carriers in a semiconducting sample. As an imaging technique it provides an advantage over more conventional approaches such as secondary ion mass spectrometry and depth‐profiling Hall voltage measurement since it provides a two‐dimensional dataset rather than a one dimensional line profile. Here, we demonstrate the utility of SCM for GaN‐based materials by assessing the unintentionally doped layer at the GaN/sapphire interface in a series of samples in which the growth conditions initially favoured the formation of three‐dimensional islands, which later coalesced to form a two‐dimensional film. Using SCM we observe that the width of the resulting conductive layer at the GaN/sapphire interface depends on the time taken to achieve coalescence but that the carrier density does not. We also assess and attempt to explain the roughness of the top surface of the conductive interface layer, which can only be addressed using an imaging technique. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)