Both electron-beam (EBIC) and photo( PCbinduced currents in p-n junctions show a sublinear dependence on beam power at high electron or photon densities /l/. In this note we account for this phenomenon, and point out that it provides a simple method for measuring the injection conditions in an EBIC or PC experiment. It is essential to know whether high o r low level injection conditions pertain when these techniques are used to measure c a r r i e r lifetimes /I/.The departure from a linear dependence of the induced short-circuit current, i is greater in diameter than the depletion region width, and we believe the observed f a l l off to be well accounted for by the phenomenon of base region spreading at high current densities /2/. Base region spreading (with attendant narrowing of the depletion region) occurs when the mobile c a r r i e r density exceeds the background doping density. Although the magnitude of this effect has been calculated for the case of c a r r i e r s injected by the junction itself in a transistor /2/ it is reasonable to suppose that a similar mechanism operates when the c a r r i e r s a r e externally injected, a s in the EBIC o r PC experiments. Indeed assuming that the depletion region narrowing is the sole cause of the sublinear behavior of isc leads t o a satisfactory agreement between our calculated and measured values of i on the incident power level, Pi, occurs when the illuminating beam sc , (displayed in Fig. 1) over a wide range of beam powers. + -+ scThe experimental data for isc were obtained using a BYXn n n p silicon power rectifier. This device is gold doped, and spreading resistance measurements indicate a resistivity in the vicinity of the junction (n-region) of 500 Qcm. 1)