We have developed a model for the calculation of the induced current due to an electron beam
with an extended generation profile. The analytical expression of the electron beam induced
current (EBIC) is obtained by solving the steady-state continuity equation using the Green
function method.
In the case of a sulphur doped (Ga0.7Al0.3As:N+/Ga0.7Al0.3As:P) sample prepared by
metalorganic vapour phase epitaxy (MOVPE) method, the experimental current profile,
measured by SEM enabled us to calculate the diffusion length of the minority carriers
(Lp = 1 μm in the N region and Ln = 1.80 μm in the P region of the ternary sample). Far from the
depletion layer, the experimental current profile measured provided us the optical self
absorption coefficient of this sample: ap = 1.483 μm−1 in the N region and an = 0.167 μm−1 in
the P region.
According to our EBIC model, the width of the depletion layer of this sample is about
0.8 μm, while at elaboration of the sample, 10 years ago, the width of the depletion layer
deduced from the characteristic curve I(V) was about 300−400 Å. This widening of the
depletion layer is due to the ageing of the diode.