Molecular-beam epitaxial growth of a far-infrared transparent electrode for extrinsic Germanium photoconductors

TL;DR

This study demonstrates the fabrication of a far-infrared transparent aluminum-doped germanium electrode using molecular beam epitaxy, achieving high transmittance, low resistivity, and good contact for use in IR photoconductors at 4 K.

Contribution

It introduces a novel MBE-grown Al-doped Ge layer as a transparent electrode meeting key optical and electrical criteria for IR detectors.

Findings

>95% IR transmittance in 40-200 microns range

Low resistivity (~5 ohm-cm) at 4 K

Successful application of MBE technology for electrode fabrication

Abstract

We have evaluated the optical and electrical properties of a far-infrared (IR) transparent electrode for extrinsic germanium (Ge) photoconductors at 4 K, which was fabricated by molecular beam epitaxy (MBE). As a far-IR transparent electrode, an aluminum (Al)-doped Ge layer is formed at well-optimized doping concentration and layer thickness in terms of the three requirements: high far-IR transmittance, low resistivity, and excellent ohmic contact. The Al-doped Ge layer has the far-IR transmittance of >95 % within the wavelength range of 40--200 microns, while low resistivity (~5 ohm-cm) and ohmic contact are ensured at 4 K. We demonstrate the applicability of the MBE technology in fabricating the far-IR transparent electrode satisfying the above requirements.