Long and middle wavelength infrared photodiodes fabricated with Hg1−x CdxTe grown by molecular-beam epitaxy

Abstract

Long and middle wavelength infrared (LWIR, MWIR) p⁺‐n photodiodes have been fabricated with Hg_1−xCd_xTe (0.20<xB lattice‐matched ZnCdTe substrates. The surface morphology was smooth and free of in‐plane twins. The Cd concentration (x) was uniform across the wafer, with standard deviations (Δx) as low as 0.0017. Structural properties were measured by double‐crystal x‐ray rocking curve and dislocation etching; FWHM values as low as 34 arcsec and etch pit density values as low as 1×10⁵ cm⁻² were measured. p⁺ ‐n homojunctions were formed by arsenic diffusion; unpassivated mesa photodiodes were fabricated by standard photolithographic techniques. MWIR and LWIR photodiodes fabricated with MBE material exhibited good diode performance, comparable to that obtained on photodiodes fabricated with the more matured technique of liquid‐phase epitaxy. 77‐K R₀A products of the diodes measured were 6.35×10⁷, 22.3, and 1.76 Ω cm² with cutoff wavelengths of 4.66, 9.96, and 12.90 μm, respectively. The R₀A product for a VLWIR photodiode was 1.36×10² Ω cm² with a cutoff wavelength of 16.23 μm at 35 K. LWIR diodes with no antireflection coating had a quantum efficiency of 48.6%. The present results represent a significant step toward the demonstration of MBE as a viable growth technique for the fabrication of large infrared focal plane arrays.