# Reflection

Reflection or reflectivity measurments are usually to examine the layer thickness of insulating layer on semiconducting substrates and epitaxial semiconductor films. The reflectance R of the structure( absorbing layer of thickness d1 on a nonabsorbing ) as show in Fig. 1(a) is given by

---------(1)

Fig.1 (a) Reflection spectroscopy schematic; (b) theoretical reflectance for SiO_{2} on Si.

T_{ox}= 100 mm, n_{0} = 1, n_{1}= 1.46, and n_{2}= 3.42,

Where ; ; ;

For a nonabsorbing layer, in Eq.(1)

The reflectance exhibits maxima at the wavelengths (max)

---------(2)

Where m = 1,2,3,…

Taking Eq.(2) at two maxima and subtracting one from the other can give the layer thickness d_{1}

---------(3)

Where i= number of complete cycles from to , the two wavelength peaks that bracket the i cycles. For example in Fig. 1(b2) for the first two peaks, i= 1, = 1.62x10^{5}cm^{-1}

and =1.22x10^{5}cm^{-1 }or i= 3, = 1.62x10^{5}cm^{-1 }and = 4.2x10^{4}cm^{-1 }is obtained a similar thickness.

[Ref.] D.K. Schroder,*Semiconductor material and device characterization*, 2^{nd} edition,John Wiley & Son,1998.