Indium-bond-and-stop-etch (IBASE) technique for dual-side processing of thin high-mobility GaAs/AlGaAs epitaxial layers

Abstract

We present a reliable flip-chip technique for dual-side processing of thin (<1 μm) high-mobility GaAs/AlGaAs epitaxial layers. The technique allows the fabrication of small (micron-scale with standard UV photolithography) patterned back gates and dual-gate structures on the thin GaAs/AlGaAs films with good alignment accuracy using only frontside alignment. The technique preserves the high-mobility (>106 cm2/V-s at 2 K) and most (>95%) of the charge density of the two-dimensional electron gas systems and allows linear control of the charge density with small (<1 V) electrostatic gate bias. Our technique is motivated by a THz quantum well detector based on intersubband transitions in a single, wide GaAs/AlGaAs quantum well, in which a symmetric, well-aligned dual-gate structure (with a typical gate dimension of ∼5 ×5 μm) is required for accurate and precise tuning of the THz detection frequency. Using our Indium-Bond-And-Stop-Etch technique, we realize such dual-gate structure on 660-nm thick GaAs/AlGaAs epitaxial layers that contain a modulation-doped, 40-nm wide, single square quantum well. By independently controlling the charge density and the DC electric field set between the gates, we demonstrate robust tuning of the intersubband absorption behavior of the 40-nm quantum well near 3.44 THz at 30 K.