a-Si DOS 측정

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a-Si DOS 측정방법에 대한 리포트

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Constant Photocurrent Method(CPM)

The optical absorption coefficient α(E)

F : the light intensity in # of photons/cm2
Ip(E,F) : the photoconductivity spectra
subscript 0 : some reference energy E0 at α0 is directly measured
β : the empirical coefficient(determined from Ip∝Fβ)

Consider a single energy level Ei with concentration Ni in the upper half of the band gap Eg = Ec-Ev of an n-type semiconductor.

In steady state,
The concentration of photogenerated electrons n is


: the optical emission rate of electrons under photon intensity F
: the density of impurity levels occupied by electrons
: the capture rate of electrons

optical emission rate ,
: the photoionization cross-section of electrons
So

(if, a homogeneous excitation(αd≪1)
the thermal emission rate from level can be neglected
for the photon energy we have (no two-step excitation))

the impurity absorption coefficient ( is given)

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