Approach from a-Ge Films for Development of High-Quality a-SiGe Films

Abstract

A-Ge:H films fabricated by means of a separated ultrahigh-vacuum reaction chamber, called the super chamber, were systematically studied. In the conventional glow-discharge method, there is a very narrow substrate-temperature region for fabricating high-density a-Ge:H films; that is, a minimum deposition rate and a maximum refractive index were obtained at about 250°C. From the point of view of optoelectrical properties, it was clear that not only rigidity of the film network but also total hydrogen content are important. In order to satisfy the two above-mentioned factors simultaneously, a low substrate-temperature high hydrogen-dilution method was effective, and film properties of a-Ge:H were largely improved; δ_d∼4.0×10^-5 Ω^-1 cm^-1, δ_ph∼1.5×10^-4 Ω^-1 cm^-1, B value ∼803 (eV·cm)^-1/2, and the ESR spin density ∼1.5×10¹⁷ cm^-3.