Gallium Arsenide (GaAs) - Courses

446 A. Borghesi and G. Guizzetti
in concentrated bromine. In the other cases no description of the surface
treatment was given.
The R values in the infrared from various labs agree to within the experimental
uncertainty. It was determined that differences in the free-carrier concentration
had no effect on R. The n values for A :::::: 50 Jim from Parsons and
Coleman [3] and Abagyan et al. [4] present a difference of 0.28% at A =
50 Jim, which lowers to 0.2% at A = 1000 Jim. In Abagyan et al. [4] the error
fln in n, resulting from the measurement of the sample thickness and of wavelength
A, is quoted not exceeding 0.005, while in Parsons and Coleman [3] n
is quoted with four decimal places and its values are those reported in Table
IV for 50 Jim S; A S; 400 Jim.
Parsons and Coleman [3] fit the infrared data and the accurate n data
from Bond [9] and Nelson and Turner [13] in the 0.5-4.0-Jim range by
using for the complex dielectric function g the following form proposed by
Barker [2]:
i.e., a classical-oscillator equation, where Si' vf, and Yi are the osciIIator
strength, restoring force, and linewidth, respectively. The second term in Eq.
(1) represents the electronic contribution and the third one the lattice contribution
with frequency-dependent damping. The fit parameters, given in
Table III, are the same used by Barker [2] to fit IX, R, and Raman data near
the transverse optic mode, except So, which had to be increased from 2.01 to
2.056 for best fit. The net result of this fit is that the refractive index of GaP
can be calculated from Eq. (1) to an accuracy somewhat better than four
figures from microwave to visible frequencies. In particular, in the range
30-200 Jim the fit agrees with the experimental n to a few units in the fourth
decimal place (±0.03%) and yields the precise value eo = 11.147 for the static
relative dielectric constant. In Table IV we have labeled this fit with nf for
the data of Barker [2].
Also, Pikhtin et al. [7] proposed an analytic dispersion relationship for
n in the 0.5-1000-Jim spectral range; it has only six parameters and is simpler
than Eq. (1) but less accurate (±0.8%). However, it is useful to report it,
since by means of a relation in Pikhtin et al. [7] it has been possible also
to fit spectra at 105 K. The fit parameters are from Pikhtin et al. [7].
For frequencies above or below V T == vo, the k spectrum has considerable
structure and values much higher than those predicted from Eq. (1).
Since the same bands are observed in compensated and uncompensated
samples, they are attributed to absorption by the lattice (combination bands)
[1, 2]. However, the IX spectra from different labs are in qualitative but not
in quantitative agreement. In the 12-20-Jim region we have tabulated the