Semiconductor physics
With minority carrier diffusion coefficient D and lifetime τ, which expression gives the diffusion length L?
- AL = D / τ
- BL = √(D × τ)
- CL = D × τ
Show answer and explanation
Answer: B. L = √(D × τ)
The diffusion length is the approximate distance minority carriers diffuse before recombining, given by L = √(Dτ). It becomes longer as the lifetime or the diffusion coefficient increases. It is an important quantity that determines the characteristics of solar cells and bipolar transistors.
- A. D / τ has units of cm²/s², not a length.
- B. Correct. The diffusion length is √(Dτ).
- C. D × τ has units of cm², not a length.