2, Singapore MIT Alliance for Research and Technology Centre, Singapore, , Singapore
Mid-infrared detection devices, which are employed in medical imaging, gas sensing, security surveillance and navigation sensing system applications, are essential components in an internet of things platform. InSb is one of the promising candidates for mid-infrared detection devices. It has a room temperature bandgap energy of 0.17 eV and is capable of detecting photon with a wavelength up to 7.3 µm. Growth of InSb on Si overcomes the restrictions of InSb substrate, which are expansive, small size (< 4 inches in diameter) and low ruggedness . Hetero-epitaxy growth of InSb devices on Si is also one of approaches to realize the integration of mid-infrared InSb with Si-based electronic devices on a single wafer, without requiring any wafer bonding process. However, the growth of InSb on (100) Si substrate is challenging due to their large lattice mismatch (19.3 %) and different lattice structures (zinc blende vs. diamond), resulting in high density of defects. Furthermore, direct growth of InSb on (100) Si surface is prohibited because of the formation of In metallic islands on Sb-terminated Si surface instead of InSb film . Therefore, an intermediate buffer layer between InSb layer and Si substrate is needed. In this report, we demonstrated two different intermediate buffer: Ge/GaAs buffer and AlSb/GaSb buffer.
Growth of InSb on a 6° offcut Si substrate using an AlSb/GaSb intermediate buffer was carried out using a molecular beam epitaxy (MBE) system. A 5nm AlSb island was firstly grown, followed by a 100 nm GaSb layer. Subsequently, a 50 nm AlSb layer was grown. Finally, a 0.8 µm InSb was grown on the AlSb surface using interfacial dislocation array to accommodate lattice mismatch. At the initial growth stage of InSb, a spotty RHEED pattern was observed and changed to a clear (1×3) after ~1 minute of growth. Using this InSb layer, an InSb photoconductor was fabricated and its photo-response was measured.
In Ge/GaAs buffer, growth of Ge on Si substrate was carried using a MOCVD system. Growth of GaAs and InSb was carried using a MBE system. Lattice-mismatch (14.6%) strain between GaAs and InSb was accommodated by an interfacial misfit (IMF) array formed at InSb/GaAs interface, which consisted of uniformly distributed 90° misfit dislocations . TEM observation exhibited a low defect density in InSb layer. An InSb p-i-n photo-detector structure was grown. Spectral response of the InSb photodetector with the detector area of 0.0285 mm2 was measured using a Fourier Transform Infrared (FTIR) spectrometer with a KBr beam splitter from 80 K to 200 K.
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