ABSTRACT
Carbon is an attractive dopant for Gallium arsenide-based devices that require high doping concentrations and low atomic diffusivities. Hole mobilities reported for heavily carbon-doped samples, moreover, are at least 30% higher than those in beryllium or zinc-doped layers. However there appears to be a discrepancy between the total amount of carbon incorporated during growth, as measured by Secondary Ion Mass Spectrometry concentration profiles, and the effective hole concentration as measured by Hall effect and Polaron electrochemical capacitance-voltage depth profiles. The authors have directly measured the presence of interstitial carbon in carbon-doped epilayers grown by MOCVD and MOMBE. Interstitial carbon could be detrimental to device performance if its diffusion out of the doped layer is rapid. By comparing the signals obtained when the beam was either randomly or critically aligned with axial channeling directions in the sample, direct determinations of interstitial carbon present in the epilayers is possible.
