PureGaB p+n Ge diodes grown in large windows to Si with a sub-300nm transition region

• Published in: Solid-state electronics 2012-08, Vol.74, p.126-133
• Main Authors: Sammak, Amir, Qi, Lin, de Boer, Wiebe B., Nanver, Lis K.
• Format: Article
• Language: English
• Subjects: Chemical vapor deposition; Epitaxial growth; Ge diodes; Ge-on-Si; PureGaB; Ultrashallow junctions
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2012.04.023

► Monocrystalline Ge-on-Si is grown in large windows with ∼ 300nm transition region. ► Growth is at 700°C in a standard Si/SiGe CVD epi-system with an extra line for TMGa. ► A p+ doped Ge surface is made by deposition of pure Ga followed by pure B (PureGaB). ► PureGaB provides low-ohmic p+ contacting and a barrier layer to Al metallization. ► PureGaB Ge-on-Si p+n diodes are nm-shallow and have uniquely low dark current. Ultrashallow junction Ge-on-Si p+n diodes have been fabricated using an epitaxial growth technique of crystalline Ge on Si substrates in a standard ASM Epsilon 2000 CVD reactor. An As-doped Ge is first deposited selectively at the temperature of 700°C where most of the lattice mismatch-defects are trapped at the interface of Ge and Si and vanish within the first 300nm of Ge growth. Under this condition, good quality single crystal Ge is grown within a layer thickness of approximately 1μm on different window sizes up to hundreds of μm2. For p+n junction fabrication, the process is followed in the same reactor with a sequence of pure-Ga and then pure-B depositions, to form an ultrashallow p-doping of As-doped Ge-islands that can be metallized by Al. The term PureGaB is introduced for this technology. The I–V and C–V characterization the diodes confirms the good quality of the ultrashallow junction Ge diodes with ideality factors of less than 1.1 and reliable low saturation currents. The doping levels are shown to be such that the depletion over the diodes falls within the Ge region.