I am studying some aspects of MOS caps with aluminum oxide as the gate oxide. I have read in some articles that x-intercept of 1/C^2 vs gate voltage (Vg) gives flat band voltage (Vfb). But this method of finding Vfb is not given in any standard books like Nicollian & Brews Donald Neamen, S.M.Sze etc. I know how to find Vfb by other methods. Can somebody in the field tell me what is the importance of the x-intercept of 1/C^2 vs Vg curve? Does it represent the cumulative effect due to work function difference (Phi ms) and band ending due to all kinds of charges in the oxide material and interface charge effects? I know that slope of the linear portion of this curve can be used to find doping concentration. My doubt is about the physical relevance of x-intercept.
According to "Semiconductor Material and Device Characterization" by Dieter K. Schroder - 2006 -
" ,φB(C –V ) is approximately the flat-band barrier height because it is determined from the 1/C2 –V curve for 1/C2 → 0 or C →∞ indicating sufficient forward bias to cause flat band conditions in the semiconductor".
i think it means that its just equal to the work function difference (flat-band barrier height) as you found above
regards
Dear Dr. Rajeev
some sources define flat-band voltage as the voltage at which the total capacitance of the MIS reaches 90% of the Ci , you can verify the above mentioned method by comparing the results with other methods, its a wonderful idea if it can be proved.
regards
Dear Abdulghefar,
I have already done that. Cfb was calculated using another equation and the voltage corresponding to that was 'read' from the CV curve. This is one method of finding Vfb which is given in Nicollian & Brews (N&B). The Cfb which is thus obtained is 95 to 98% of Ci. That part is OK. But when I take the x- intercept of 1/C^2 vs Vg curve I get a very small value (1/3 rd ). It is only equal to the Phi ms.(ie. work function difference of metal and semiconductor). So my doubt is whether the x-intercept denotes only the work function difference rather than Vfb as claimed in some papers. Or can we say that x-intercept is equal to Vfb, only if the band bending is due to work function difference alone (ie. no oxide charges or interface charges present).
Thanks and regards,
Rajeev.
According to "Semiconductor Material and Device Characterization" by Dieter K. Schroder - 2006 -
" ,φB(C –V ) is approximately the flat-band barrier height because it is determined from the 1/C2 –V curve for 1/C2 → 0 or C →∞ indicating sufficient forward bias to cause flat band conditions in the semiconductor".
i think it means that its just equal to the work function difference (flat-band barrier height) as you found above
regards
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