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. This paper was presented at the Electronic Materials Conference at MIT, Cambridge, 1992.