|
(mc14)
where the generation in the depletion layer was assumed to be constant. The rate of change required to observe deep depletion is then obtained from:
(mc15)
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| bet | 49/57 | | Sana | 09.05.2021 | | Hajmi | 0.62 Mb. | | #14427 |
(mc14)
where the generation in the depletion layer was assumed to be constant. The rate of change required to observe deep depletion is then obtained from:
(mc15)
This equation enables to predict that deep depletion is less likely at higher ambient temperature since the intrinsic concentration ni increases exponentially with temperature, while it is more likely to occur in MOS structures made with wide bandgap materials (for instance SiC for which Eg = 3 eV) as the intrinsic concentration decreases exponentially with the value of the energy bandgap.
In silicon MOS structures one finds that the occurance of deep depletion can be linked to the minority carrier lifetime: while structures with a long (0.1 ms) lifetime require a few seconds to reach thermal equilibrium which results in a pronounced deep depletion effect at room temperature , structures with a short (1 ms) lifetime do not show this effect.
Carrier generation due to light will increase the generation rate beyond the thermal generation rate which we assumed above and reduce the time needed to reach equilibrium. Deep depletion measurements are therefore done in the dark.
Experimental results and comparison with theory
As an example we show below the measured low frequency (quasi-static) and high frequency capacitance-voltage curves of an MOS capacitor. The capacitance was measured in the presence of ambient light as well as in the dark as explained in the figure caption.
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Bosh sahifa
Aloqalar
Bosh sahifa
(mc14)
where the generation in the depletion layer was assumed to be constant. The rate of change required to observe deep depletion is then obtained from:
(mc15)
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