Characterization of selective reactive ion etching effects on delta-doped GaAs/AlGaAs MODFET layers

The effects of selective reactive ion etching (SRIE) using SiCl₄/SiF₄ plasma on delta-doped GaAs/Al_0.3Ga_0.7As modulation-doped field-effect transistor (MODFET) structures and devices have been investigated. The results are compared with those of corresponding conventionally doped MODFETs. Hall measurements were conducted at 300 and 77 K to characterize the change in the transport properties of the two-dimensional electron gas due to low energy ion bombardment during the SRIE process. Delta-doped structures showed a smaller change in sheet carrier density and mobility compared to conventionally doped structures. Direct current and high frequency measurements were performed on the SRIE gate-recessed MODFETs. No significant change in threshold voltage was observed for the delta-doped MODFETs in contrast to an increase of about 300 mV for the conventionally doped MODFETs processed at a plasma self-bias voltage of -90 V and a 1200% overetch time. Maximum dc extrinsic transconductance and unity current gain cutoff frequency did not change with SRIE processing for either of the structures.