Indium-Bond-And-Stop-Etch (IBASE) Technique for Dual-side Processing of Thin High-mobility GaAs/AlGaAs Epitaxial Layers

TL;DR

This paper introduces the IBASE technique enabling dual-side processing of ultra-thin GaAs/AlGaAs layers, preserving high mobility and charge density, and demonstrating precise control of intersubband absorption for THz detectors.

Contribution

The paper presents a novel flip-chip IBASE method for dual-side processing of thin high-mobility GaAs/AlGaAs layers with high alignment accuracy and minimal mobility loss.

Findings

High-mobility GaAs/AlGaAs layers retain >95% charge density

Dual-gate structures enable linear charge density control

Tuning of intersubband absorption near 3.44 THz demonstrated

Abstract

We present a reliable flip-chip technique for dual-side processing of thin (<1 micron) 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 (>10^6 cm^2 /V-s at 2 K) and most (>95%) of the charge density of the 2-dimensional electron gas (2DEG) systems, and allows linear control of the charge density with small (< 1 V) electrostatic gate bias. Our technique is motivated by a novel 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 micron by 5 micron) is required for accurate and precise tuning of the THz detection frequency. Using our Indium-Bond-And-Stop-Etch (IBASE) 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.