Electrical & Computer Engineering, Department of
Date of this Version
9-15-1991
Abstract
Pseudodielectric functions (ε) = (ε1) + i (ε2) of GaAs were measured by spectroscopic ellipsometry (SE), in the range of 1.W.45 eV, at temperatures from room temperature (RT) to ~610 ° C. A very clean, smooth surface was obtained by first growing an epitaxial layer of GaAs on a GaAs substrate and immediately capping it with a protective layer of arsenic. The cap prevented surface oxidation during transport to the measurement chamber, where it was evaporated under ultrahigh vacuum at ~350 °C. Room-temperature SE results from this surface are in good agreement with those in the literature obtained by wet-chemical etching. A quantitative analysis of the (ε) spectrum was made using the harmonic-oscillator approximation (HOA). It is shown by the HOA that the E1 and E1 + Δ1 energy-band critical points shift downward ~300 meV as temperature increases from RT to ~610 °C. An algorithm was developed, using the measured optical constants at a number of fixed temperatures, to compute the dielectric function spectrum at an arbitrary temperature in the range of 22-610 °C. Therefore, the ellipsometer can be utilized as an optical thermometer to determine the sample surface temperature.
Comments
Published in J. Appl. Phys. 70 (6), 15 September 1991. Copyright 1991 American Institute of Physics. Used by permission.