Development of far-infrared Ge:Ga photoconductor having a longitudinal configuration

Abstract

In order to efficiency obtain a two-dimensional (2D) image in the 3 THz range, it is important to develop a 2D far-infrared detector array. We have developed a gallium-doped germanium (Ge:Ga) far-infrared photoconductor that has a longitudinal configuration. This structure is suitable for a large format monolithic 2D array. In this letter, we show that a transparent electrode that is responsive in the far-infrared range can be formed by ion implantation, and this layer contributed to increasing quantum efficiency. We obtained a high responsivity (16.2 A/W) and good noise equivalent power (2.6×10−17 W/Hz1/2) of Ge:Ga photoconductor in longitudinal configuration by combination of ion-implanted layers and Ge:Ga bulk material.

Molecular-Beam Epitaxial Growth of a Far-Infrared Transparent Electrode for Extrinsic Germanium Photoconductors

“…At the growth interface, the profile shows an exponential decrease with the scale length of 2 × 10 À3 μm, which is about an order of magnitude lower than that obtained from the ionimplantation technology (Fujiwara 2000). In our MBE system, we demonstrated high controllability for both doping concentration and profile.…”

“…Measured data distribute around T IR;d ¼ 1:0 (40 ≤ λ ≤ 200 μm), whereas those for ion-implanted samples show T IR;d ¼ 0:6-0:7 (e.g. Fujiwara 2000). Thus, there is no significant far-IR absorption in the Al-doped Ge layer.…”

“…Therefore, the formation of the decreasingly-doped layer as a function of implant depth is inevitable. Such a broad doping profile significantly degrades far-IR transmittance due to photon absorption within the thick-implanted layer by free carriers and doped impurities (Hadek et al 1985;Fujiwara 2000). Nevertheless, there are few investigations in terms of abruptness for the doping profile.…”

Monolithic Ge:Ga Detector Development for SAFARI

“…For that purpose, we have tested three parameters including 2, 5, 10 × 10 13 [ions cm −2 ], which are 1/2, 1, and 2 times of the implantation for the AKARI detector (Fujiwara, 2000). A figure of test pieces for the resistivity measurement is shown in Figure 3 and the results are shown in Figure 4.…”

An electronic read-out circuit for time-domain terahertz imaging with photoconductive antennas

“…The arrays may be one-or two-dimensional linear arrays as used in CCD cameras, but it is also possible to prepare other arrangements for specialized equipment, for example in T-ray tomography. Fujiwara [11] recently presented an antenna array for THz radiation based on Ge:Ga photoconductors to be used in astronomy, but they are unsuitable for time-domain spectroscopy and need cooling to 4.2 K.…”