Application of Iron-doped GaAs to Optically-Controlled Variable Resistors

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In the first year, GaAs diodes of pi/n^+ structure were fabricated by use of overcompensation of donors by diffused iron deep acceptors. Meanwhile, iron concentrations in the diffused regions were analyzed. The depth profiles are remarkably flat and the concentration ranges from 10^<15> to 10^<17>A/cm^3 depending on the diffusion temperature of 650-900ﾟC,which result have been published in the Japanese Journal of Applied Physics. Selective inversion of conductivity type by iron-diffusion was successful to produce a pi/n^+/pi structure for the present device.In the second year, diodes with lower iron concentration were fabricated from bulk and epitaxial GaAs materials, and their current-voltage characteristics were examined. Leakage current as low as 1x10^<-9> A/cm^2 and high breakdown voltage over 500 V were realized, but the junction characteristics were found to depend strongly on the starting material. These considerations resulted in a pi/n^+/pi mesa structure with a pair of interdital electrodes on the surfaces and a back electrode to temporarily bias the device. The resistance of the surface pi-layr changes by a factor over 10 after the structure is biased, and recovers to the initial value when weakly illuminated. The high-resistance state caused by the stored charge in the layred structure decays in a few minutes, which limits its application to dynamic operations.To further extend its applicability, the charge storage time must be increased by reducing the leakage current. Also, the present study suggests that a similar structure may be a candidate for an ultra-fast photodetector, which will be under investigation soon.