Damage-free lift-off of epitaxial HgCdTe thin films for future curved infrared imaging array applications

This paper presents a study on the molecular beam epitaxial (MBE) growth of ${Hg}_{0.72}{Cd}_{0.28}Te$ thin film materials on ${Cd}_{0.96}{Zn}_{0.04}Te$ (2 1 1)B substrates, incorporating a 10 nm thick MgTe sacrificial layer for subsequent lift-off. The ${Hg}_{0.72}{Cd}_{0.28}Te$ thin films present a full width at half maximum of 31 arc sec for the X-ray diffraction rocking curve and a root-mean-square surface roughness of 1.2 nm. Additionally, this study developed and characterised an epitaxial lift-off process for the HgCdTe epilayers. The HgCdTe epilayers were successfully lifted-off from the substrate by adhering them to a silicon substrate and immersing in deionized water to dissolve the MgTe sacrificial layer. After lift-off, the samples exhibited p-type conduction with a carrier concentration of $2.01\times {10}^{15}$ ${cm}^{-3}$ and a hall mobility of $1.96\times {10}^2$ ${cm}^2/V·s$ at 77 K. Following the epitaxial lift-off process, photoconductors were fabricated on the HgCdTe thin films, which demonstrated a peak responsivity of 1080 $V/W$ and a peak detectivity of $3.3\times {10}^{10}$ Jones at 77 K at the wavelength of 5.4 µm. The minority carrier lifetime was measured to be around 1.15 µs at 77 K. A scanned imaging system was constructed to assess the infrared imaging performance of the photoconductor. These results were then compared with those of a photoconductor fabricated on HgCdTe thin films without the epitaxial lift-off process, and indicated that the lift-off process has minimal impact on the optoelectronic properties of the thin film and on device performance. These findings validate the feasibility of producing high quality, free-standing HgCdTe thin films for future applications in curved imaging arrays.