A simplified technique for measuring fast surface states

Abstract

A technique is presented which measures the number of fast states (/cm 2) between (flat band) φ s = 0 and φ s = 2 φ B using a high frequency C − V and d.c. ramp I − V tracing of any MIS capacitor. For cases where fast state densities near flat band are insignificant, the true flat band point V( φ s = 0) is obtained from the high frequency C − V curve. Then from the ( I − V) curve the V( φ s = 2 φ B ) point is obtained by graphically measuring off an area = I max (2 kT/ q) ln ( N B / ni) between V = V FB , V = V 1, I = Imax, and I − V curve. Then the fast state density ( N FS (/cm 2)), is obtained from the expression: Vφ s = 2φ B − Vφ s = 0 = 2φ B + q C ins [N si + N FS] where all values are known. For cases where significant fast states exist near flat band, the true flat band point can be obtained graphically from the I − V tracing using any value of surface potential near mid gap calculated from the high frequency capacitance.