Admittance spectroscopy analysis of the conduction band offsets in Si/Si1-x-yGexCy and Si/Si1-yCy heterostructures

Schottky diodes fabricated on in situ doped n-type Si/Si1-x-yGexCy/Si heter ostructures grown by chemical vapor deposition were used for admittance spe ctroscopy in order to study the impact of carbon on the conduction band off sets. Samples with a nominal Ge concentration of 20 at. % and carbon fracti ons up to 1.3 at. % were studied. In these experiments, the measurement fre quency was swept continuously from 1 kHz to 5 MHz, and the temperature was scanned in small increments from 20 to 300 K. Admittance signals in these s amples were found to originate from three sources, namely doping freeze-out , band offsets, and traps. Signals arising from the band offsets indicate a conduction band edge lowering for Si/Si1-x-yGexCy of similar to 33+/-22 me V/at.% C. A trap-related admittance signal at an energy of 228+/-25 meV bel ow the Si conduction band was observed in the Si1-x-yGexCy sample with the highest C fraction (1.3 at. %). The trap energy measured by admittance spec troscopy is in close agreement with the activation energy of 230 meV, which has been reported in the literature for a complex involving interstitial c arbon. The conduction band offset in a Si/Si1-yCy sample with 0.95 at. % C was also measured by both admittance spectroscopy and Schottky capacitance- voltage profiling. The two techniques yield excellent agreement, with Si/Si 0.9905C0.0095 conduction band offsets of 48+/-10 and 55+/-25 meV, respectiv ely. (C) 1999 American Institute of Physics. [S0021-8979(99)07802-0].