AlGaAs/GaAs modulation-doped structures grown on a Be-ion-implanted GaAs back gate

Novel back-gate devices, in which the two-dimensional electron gas (2DEG) at the heterointerface is controlled by a voltage applied to the underlying Be-implanted p-type region, are successfully fabricated by using focused Be-ion-beam scanning and MBE overgrowth of an AlGaAs/GaAs modulation-doped structure For the pn-junction-type back-gate structure, the control of the 2DEG is realized without inserting an AlGaAs barrier layer between the 2DEG and the back gate. The Be out-diffusion into the overgrown layer increases with increasing Be ion dose. However, the sharp front of the Be out-diffusion enables us to fabricate the devices with a small separation between the 2DEG and the p-type back gate. Even for a separation less than 150 nm, the damage due to Be out-diffusion is negligibly small. The gate leakage current is small when the back-gate voltage is less than 1.5 V where a forward current starts to flow through the pn junction. Within this voltage limit, the carrier density of the 2DEG was well modified in the range of (1-6) × 10¹¹ cm^-2. Trap-filling effects due to a large forward current through the pn-junction-type gates are also discussed.