Effects of reactive ion etching on GaAs/AlGaAs heterostmctures

The effects of selective reactive ion etching (SRIE) in SiCl₄: SiF₄ plasmas on modulation-doped GaAs/Al_0.3Ga_0.7 As heterostructures have been investigated. Hall effect measurements were conducted to determine SRIE effects on carrier mobility and electron sheet concentration of the two-dimensional electron gas (2-DEG). Samples were etched at several plasma self-bias voltages and for extended etch periods with Hall effect measurements conducted at 300 and 77 K. Results show reductions in the 2-DEG carrier concentration and mobility with increasing plasma self-bias voltage and increasing etch time at both room and liquid-nitrogen temperatures. The reduction in electron concentration after etching can be attributed to the creation of traps in the AlGaAs donor layer due to bombardment with the low-energy ions present in the plasma. Mobility reduction is due to the increasing importance of remote impurity scattering as electron sheet concentration decreases. These degradations in electron concentration and mobility are sufficiently minimized for low plasma self-bias voltages (-30 V), and short etch time such that the SRIE process should be useful for fabricating modulation-doped field-effect transistors.