Page 69 - Chalcogenide Glasses for Infrared Optics

Chalcogenide Glasses 47

Dielectric Frequency Resistivity
Glass Constant (cps) (Ω . cm)(300K)
Ge As Se 5 × 10 10
15 15 70
Si Sb S 9.6 × 10 7
15 15 70
Ge P Se 9.3 × 10 10
15 15 70
Si Sb S 14 100 2 × 10 9
15 35 50
Si As Te 5 × 10 5
6 9 45
Ge As Te 2 × 10 7
2 3 15
Si Ge As Te 24 1 kc 1 × 10 8
3 2 5 10
Ge P S 9 × 10 9
3 6
GeAs Te 5 × 10 5
4 5
Si As Te 5 × 10 9
4 3 3
GeAs Te 2.8 × 10 4
2 7
TABLE 2.8 Electronic Conduction of Some Chalcogenide Glasses

2.5.5 Electrical Properties
It was mentioned earlier in Chap. 1 that chalcogenide glasses are
electronic conductors and their properties have been the subject of
intense study, but not in this program. Early on at TI, it was found
that some glasses containing Te and Sb could become good con-
ductors with low resistivity but poor infrared transmission. Some
electrical measurements carried out on 11 compositions are listed
in Table 2.8. From the values, it is clear that the glasses used optically
may be called high-resistivity semiconductors ranging in values from
10 to 10 ohm ⋅ cm at room temperature. The two measured dielectric
10
4
constants were high. What is not shown in the table is the fact that
these glasses are electronic conductors with very low mobility for
their electrons or holes involved in the conduction process. The poor
mobility is the result of the nature of glass. All glasses are disordered
solids.

2.5.6 Physical Strength
At this point in time, the large samples with flawless physical quality
required for meaningful measurements were not available. Some
attempts to measure the tensile strength breaking fibers were made
but with poor results. Most all the fibers had surface flaws. Ultimate
tensile strength ranged from 500 to 1000 psi for three samples judged
flawless. Later, we will discuss physical strength of glasses based on
rupture modulus tests and the determination of Young’s modulus
and the shear modulus from acoustical measurements.