The determination of impact ionization coefficients in (100) gallium arsenide using avalanche noise and photocurrent multiplication measurements

The electron and hole impact ionization coefficients in (100) GaAs have been determined using photomultiplication measurements performed on specially fabricated p
⁺
-n diode structures having active region carrier concentrations from 1.1 X 10
¹⁷
to 2.2 X 10
¹⁵
cm
^-3
. These structures are designed to permit pure electron and hole injection in the same diodes. In diodes having heavy p
⁺
doping, the effects of electron dead space have been observed. This dead-space region corresponds to the distance required for an injected carrier to accelerate ballistically to the impact ionization threshold energy, and a method to include this phenomenon in the calculation of α and β from the experimental multiplication data is presented. Agreement among the results from all these structures is obtained with an electron threshold energy of 1.7 eV, and the corrected data are also in agreement with data obtained from device structures designed to eliminate dead-space effects. The measured ratio of α/β in GaAs is found to decrease from 2.4 at 2.2 X 10
⁵
V/cm to 1.0 at 6.25 X 10
⁵
V/cm. Avalanche noise measurements performed at 30 MHz on the same devices under both electron and hole injection yield a k
_eff
of 0.6 and a k'
_eff
of 1.7, respectively, in agreement with the values of these parameters obtained from the photocurrent results.