Electro-optic probing of GaAs

Electro-optic probing is a method of measuring potential profiles in semiconductor devices. Potential profile measurements were taken on simple capacitor devices by using C-W laser (ND-YAG, 1064 nm). These measurements show very curious results. Potential profiles were very irregular even for such simple device structures. It is suggested that the Fabry-Perot effect is acting as a large source of noise in the measurement technique. To resolve this problem we have investigated two groups of devices one set with very rough surfaces, the other one with very smooth surfaces. The results show that in the rough surface set, the potential profiles across the area of the capacitors are very irregular. In the smooth samples the measured potential profiles are as expected. These differences in the results show that the noise on the electro-optic signal is due to the FP effect. We have further investigated the potential profiles in gate-less MESFET devices. The same noise effect due to the Fabry-Perot effect is observed. We also note an unexpected feature which we discuss.