Fig. 2. Characterizing the effective area by the scanning photocurrent mapping.

a–e Photocurrent mapping illustration of the distribution of the response with beam centered at different positions with optical responses shown in Fig. 1g. f–k Illustration of cumulated mapping signal with different beam wrist. S₁, S₂, and S₃ in f–h are scanning photocurrent signals of Gaussian beam with beam wrist comparable to the length of the small region (denoted as $\mathrm{\Delta }A$) near the characteristic length at different positions. S’₁, S’₂, and S’₃ in i–k are the signals with beam wrist larger than the characteristic length. The dashed blue lines in h and k show the cumulated signal at $\mathrm{\Delta }A$, which are equal in the two cases.