50. Silicon-germanium alloys have been used in certain types of solar cells. The paper “Silicon-Germanium Films Deposited by Low-Frequency Plasma-Enhanced Chemical Vapor Deposition” (J. of Material Res., 2006: 88–104) reported on a study of various structural and electrical properties.

Consider the accompanying data on x
Ge concentration in solid phase (ranging from 0 to 1) and y
Fermi level position (eV):

A scatter plot shows a substantial linear relationship. Here is MINITAB output from a least squares fit. [Note: There are several inconsistencies between the data given in the paper, the plot that appears there, and the summary information about a regression analysis.]

The regression equation is Fermi pos = 0.7217 – 0.4327 Ge conc S = 0.0737573 R-Sq = 80.2% R-Sq(adj) = 78.4%

Analysis of Variance Source DF SS MS F P Regression 1 0.241728 0.241728 44.43 0.000 Error 11 0.059842 0.005440 Total 12 0.301569