Selective Etching and Micro-Transfer Printing of GaSb-Based Infrared Devices

III-V-Antimonide (Sb) compounds are useful for many different infrared device applications, ranging from full spectrum photovoltaics, to eye-safe photonic power converters, to light-emitting diodes for biomedical applications. The ability to remove the III-V-Sb device from its native substrate and heterogeneously integrate it with different materials would further support these technologies. For GaSb-based devices, heterogeneous integration is typically achieved by inverting the device, bonding the epitaxial surface to a new handle, and etching through the substrate. However, this method is not compatible with substrate reuse or additive manufacturing capabilities that could be provided with micro-transfer printing. Though complete substrate removal is undesirable in some aspects, it is typically the most successful method of separating a sample from its substrate due to the low etch selectivity between 6.1 Å semiconductors.<br/><br/>Our group has characterized etch selectivity between AlGaAsSb/InAsSb lattice matched to GaSb when using citric acid-based etches as well as hydrofluoric acid (HF) based etches [1]. Using 1:5 ratios of citric acid (C₆H₈O₇) and hydrogen peroxide (H₂O₂), an etch selectivity ratio of 852 was found between InAsSb/Al0.33GaAsSb, with InAsSb etching vertically at a rate of 554 nm/min. Alternatively, using an etch mixture of 1:1:100 HF:H₂O₂:H₂O cooled to 10 °C yielded a vertical etch rate of &gt;8000 nm/min for AlGaAsSb, but only resulted in an etch selectivity ratio of 171.5 for AlGaAsSb/InAsSb. To investigate how these vertical etch rates translated into lateral undercut rates, we grew 2 µm of AlGaAsSb membranes on top of InAsSb sacrificial and AlGaAsSb etch-stop layers, monitored progression of the lateral etch by infrared microscopy. While vertical etch tests demonstrated etch rates of InAsSb at ~554 nm/min, lateral etch rates were found to be significantly slower. To decrease the overall time required to undercut the device, the temperature of the solution can be increased without negatively impacting the etch selectivity. Using these findings, photovoltaic cells and quantum-well LEDs were grown by molecular beam epitaxy on GaSb substrates. Devices were fabricated on-substrate and immersed in a solution of 1:5 C₆H₈O₇:H₂O₂ for selective release. The importance of the thickness of the sacrificial etch layer, the tethering scheme, and the composition of the dielectric protection layer were explored to improve the etch-release yield and device performance.<br/>[1] M. A. Stevens, et al. “Selective Etching of 6.1 Å Materials for Transfer-Printed Devices,” in <i>IEEE 49th Photovoltaics Specialists Conference (PVSC)</i> (2022) 0240-0243