Question

Why Alpha is taken negative in case of semiconductors

Answer 1

Answer:

temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property R that changes when the temperature changes by dT, the temperature coefficient α is defined by the following equation:

{\displaystyle {\frac {dR}{R}}=\alpha \,dT}{\displaystyle {\frac {dR}{R}}=\alpha \,dT}

Here α has the dimension of an inverse temperature and can be expressed e.g. in 1/K or K−1.

If the temperature coefficient itself does not vary too much with temperature and {\displaystyle \alpha \Delta T\ll 1}{\displaystyle \alpha \Delta T\ll 1}, a linear approximation will be useful in estimating the value R of a property at a temperature T, given its value R0 at a reference temperature T0:

{\displaystyle R(T)=R(T_{0})(1+\alpha \Delta T),}R(T) = R(T_0)(1 + \alpha\Delta T),

where ΔT is the difference between T and T0.

For strongly temperature-dependent α, this approximation is only useful for small temperature differences ΔT.

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