Optimization of the electrical conductivity and thermal coefficient of temperature (TCR) on hydrogenated amorphous silicon-germanium films doped with nitrogen (a-SiGe:H,N) for applications on high performance infrared detectors

Uncooled microbolometers are infrared detectors used for imaging applications in the long-wave IR spectra, made of semiconductor materials, such as vanadium oxide (VOx), boron doped amorphous silicon (a-Si:H,B) or amorphous silicon germanium (a-SiGe:H), the last two are usually deposited by plasma-enhanced chemical vapor deposition (PECVD). When infrared radiation falls on the thermos-sensor films, they experience changes in their electrical resistance, generating an electrical signal proportional to the amount of incident radiation. In this work, we optimized the absorption of infrared radiation in the long-wave IR range (8-14 um) with amorphous silicon germanium films doped with nitrogen (a-SiGe:H,N). Several flow rates of nitrogen N2) and different $\mathrm{S}\mathrm{i}\mathrm{H}_{4}$ and $\mathrm{G}\mathrm{e}\mathrm{H}_{4}$ flow rate ratios have been used for the deposition of two a-SiGe:H,N film series. We have characterized the films electrical and optically, and we have studied the electrical conductivity at room temperature $(\sigma_{RT})$, which is in the range of (1.2E-8 to 6.45E-2) $(\Omega.\mathrm{c}\mathrm{m})^{-1}$ and the Temperature Coefficient of Resistance (TCR), which is in the range (2.67 to 6.23) (%/K). Those $\sigma_{RT}$ and TCR values of the a-SiGe:H,N films are very attractive for being used in high performance infrared detectors.

I. Introduction

Uncooled microbolometers are composed of a thermos-sensing thin film, which detects infrared (IR) radiation in the long-wave IR (8 - 14 um), generally made of semiconductor materials, as vanadium oxide , boron doped amorphous silicon (a-Si:H,B), or amorphous silicon germanium (a-SiGe:H). Those thermo-sensing films are suspended on a substrate insulated with a metallic reflective film by two legs, at a quarter-wavelength (2.5um) distance to improve absorbance, by forming a Fabry Perot cavity [1]. When infrared radiation falls on the thermos-sensor film, it is heated up and experience changes in its electrical resistance, which translates into an electrical signal proportional to the amount of incident radiation. A significant advantage of microbolometers is that they do not require active cooling like more traditional infrared sensors, making them more compact, lightweight, and less expensive.