Development of nanofabrication technology of metallic p-GaAs and its application to single hole transistors

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In this study, AFM-based surface oxidation process was applied for the surface modification of p-type GaAs to fabricate planar-type devices.A heavily carbon doped p^<++>-GaAs fabricated by metalorganic molecular beam epitaxy (MOMBE) with trimethylgallium (Ga(CH_3)_3 : TMG) and elemental As and a Zn-doped p-GaAs substrate were locally oxidized in air at room temperature using a commercially available AFM unit. The tip of the AFM was Au-coated Si_3N_4 with a pyramidal shape with a base scale of 4μm. A function generator was used for the source of pulsed voltage, and a semiconductor parameter analyzer was also used for the source of constant voltage. All experiments were done by contact mode AFM.By improving the shape of an AFM tip by electron-beam-induced deposition of a-C using scanning electron microscope (SEM), and by adjusting the AFM oxidation process conditions, a p^<++>-GaAs oxide wire with 10nm width was successfully fabricated. From this result, it was clear that the sizes of p^<++>-GaAs oxide wires could be controlled by adjusting the process conditions.Moreover, an AFM-based surface oxidation process, including a voltage modulation, was employed in order to improve aspect ratios of p-GaAs oxide. From a duty ratio dependence of aspect ratios of oxide dots, it was considered that optimization of an anodizing time per a cycle of a pulsed voltage was necessary. As a result, we fabricated a p-GaAs groove with 40nm width and 6nm depth at a scanning speed of 60nm/s. From these results, it became clear that pulsed voltage could be employed for the fabrication of oxide with high aspect ratio.Finally, the obtained oxide wire was successfully applied to semiconductor-insulator-semiconductor (SIS) diode as insulator. From its nonlinear I-V characteristic, it was found that the oxide wire acts as the insulating barrier material for the current.