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

在第一年，我们利用扩散铁深受主对施主的过补偿，制作了π/n^+结构的GaAs二极管。同时，分析了扩散区的铁浓度。深度分布非常平坦，浓度范围从10 <15>^ A/cm ^3到10^<17>A/cm ^3，取决于650-900 ℃的扩散温度，该结果已发表在日本应用物理学杂志上。第二年，我们成功地用体材料和外延GaAs材料制造出了具有低铁浓度的二极管，并对它们的电流-电压特性进行了测试。漏电流低至1x 10 ^<-9>A/cm ^2，击穿电压超过500 V，但结特性强烈依赖于起始材料。这些考虑导致了一个π/n^+/π梅萨结构，在表面上有一对中间电极，背面电极暂时偏置器件。结构在偏压后表面π层的电阻变化超过10倍，在弱光照射下恢复到初始值。由于层状结构中存储的电荷引起的高阻态在几分钟内就会衰减，限制了其在动态操作中的应用，为了进一步扩展其适用性，必须通过减小漏电流来增加电荷存储时间。此外，目前的研究表明，类似的结构可能是超快光电探测器的候选者，这将很快进行调查。

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.