npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041


Research Paper

New Phys.: Sae Mulli 2018; 68: 459-466

Published online April 30, 2018

Copyright © New Physics: Sae Mulli.

Characteristics of the Photocurrent Limited by the Space Charge

Hye Jin HA, Sang Ho SOHN*

Department of Science Education, Kyungpook National University, Daegu 41566, Korea


Received: December 15, 2017; Revised: February 19, 2018; Accepted: March 5, 2018

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


The relationship between the photocurrent ($I$) and the applied voltage ($V$) was evaluated theoretically by considering the space charge, and the result was compared with the experimental values. The photocurrent derived in this study varied as $V^{3/2}$, similar to the Child-Langmuir law, except for terms related to the initial velocity of photoelectrons and to the light intensity. The apparatus used for the photoelectric-effect measurement was composed of a mercury light source and a photoelectric tube with a BaO photodetector. Comparing the experimental values to the calculated ones, the photocurrent was found to depend on $V^{3/2}$ at low and reverse voltages with space charges and on $V^{1/2}$ at high voltages without them. The critical voltage of the space-charge-limited currents is related to both the intensity and the frequency of the illuminated light. The space charge is an important factor influencing the photocurrent characteristics of the photoelectric effect.

Keywords: Photoelectric effect, Photocurrent, Space charge

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