Defect Engineering in MBE-Grown CdTe Buffer Layers on GaAs (211)B Substrates

Demand for high-performance HgCdTe infrared detectors with larger array size and lower cost has fuelled the heteroepitaxial growth of HgCdTe on CdTe buffer layers on lattice-mismatched alternative substrates such as Si, Ge, GaAs and GaSb. However, the resulting high threading dislocation (TD) density in HgCdTe/CdTe limits their ultimate application. Herein, strained CdZnTe/CdTe superlattice layers have been used as dislocation filtering layers (DFL) to reduce the TDs in CdTe buffer layers grown on GaAs (211)B substrates (14.4% lattice-mismatch) by molecular beam epitaxy (MBE). Cross-sectional microstructure characterization indicates that the DFLs suppress the propagation of TDs. For optimal Zn content combined with thermal annealing, the DFLs effectively reduce the defect density of the upper-most CdTe layer from low-10(7) cm(-2) to the critical level of below 10(6) cm(-2). In comparison to conventional buffer CdTe layers, the in-plane lattice of the CdTe layers in/near the DFL region is compressively strained, leading to a spread in x-ray double-crystal rocking curve full-width at half-maximum values but better in-plane lattice-matching with HgCdTe. The combined advantages of lower dislocation density and better lattice-matching with HgCdTe indicate that the DFL approach is a promising path towards achieving heteroepitaxy of high-quality HgCdTe on large-area lattice-mismatched substrates for fabricating next-generation infrared detectors.

Automated summary

In this study, strained CdZnTe/CdTe superlattice layers were used as dislocation filtering layers to reduce the threading dislocation density in CdTe buffer layers. The results showed that the dislocation density could be effectively reduced to below the critical level by optimizing the Zn content and thermal annealing. The DFL approach offers the advantages of lower dislocation density and better lattice-matching with HgCdTe, making it a promising path for achieving heteroepitaxy of high-quality HgCdTe on large-area lattice-mismatched substrates for next-generation infrared detectors.