Characterization in Silicon Processing

ratio of the HBT collector current to that of a conventional homojunction device

as

a function of temperature

85

:

7

f

(HBT)//

f

(BJT)

-

exp(AE

v

/kT)

The

total

energy gap difference AE

g

can be found from the temperature variation

of the ratio of the HBT base current to the homojunction collector current. Modu-

lation doping measurements as a function of temperature

11

suggest that the con-

duction band discontinuity AE

C

is

small,

so that AE

g

~ AE

V

. The measured bandgap-

difference dependence on Ge content in unrelaxed films agrees

well

with optical

absorption measurements and with values predicted by band calculations.

85

Interfacial Abruptness

and

Outdiffusion ...