Very low dark current heterojunction CCD's

A model has been formulated which accounts for the major sources of dark current (J
D
) associated with a single pixel of a heterojunction, Schottky gate charge-coupled device (CCD). This model predicts the temperature dependence of J
D
and shows that for properly fabricated gates, bulk generation in the channel is the primary source of dark current. To verify the model, the dark current of Al
0.3
Ga
0.7
As/ GaAs n-p
⁺
heterostructure CCD's was measured over the temperature range 23-55°C. At room temperature,
J_{D} \approx 83
pA/cm
²
, typically, and some pixels have J
D
as low as 43 pA/cm
²
. These are the lowest dark currents reported to date for a CCD structure. The data at 55°C show that, typically, J
D
increases to ∼ 1 nA/cm
²
. Furthermore, the data confirm the temperature dependence of J
D
predicted by the model.