Suppression of strain-induced cross-hatch on molecular beam epitaxy (211)B HgCdTe

Abstract

Because the performance of HgCdTe-based photodiodes can be significantly degraded by the presence of dislocations, we have systematically investigated and suppressed lattice-mismatch-induced cross-hatch formation and the associated generation of dislocations in (211)B HgCdTe/CdZnTe. A series of HgCdTe epilayers were deposited simultaneously on pairs of substrates with differing ZnTe mole fractions. Epilayers' CdTe mole fraction and substrates' ZnTe mole fractions were measured using optical-transmission spectra. Lattice mismatch and residual strain were estimated from room-temperature, x-ray diffraction, and double-crystal rocking-curve measurements (DCRC). It was found that cross-hatch patterns were suppressed in epilayers deposited on nearly lattice-matched substrates (|Δa/asub| < 0.02%). Such epilayers exhibited excellent crystalline quality as revealed by defect-decoration etching (etch-pit density (EPD) < 105 cm-2) and x-ray diffraction (full-width at half-maximum (FWHM) ∼ 10 arcsec). In addition to determining the upper limits of lattice mismatch needed to eliminate cross-hatch, we investigated the use of reticulated substrates as a means to suppress cross-hatch. We found that growth on reticulated mesa structures (<100 µm)with edges parallel to [01-1] resulted in epilayers with substantially reduced cross-hatch-line densities despite large lattice mismatch (Δa/asub < 0.04%). The use of reticulated substrates could suppress cross-hatch because of lateral-alloy variation in large substrates and complex multistack epilayers (e.g., multicolor detectors).