In-situ gallium-doping for forming p+ germanium-tin and application in germanium-tin p-i-n photodetector

• Published in: Journal of applied physics 2016-04, Vol.119 (15)
• Main Authors: Wang, Wei, Vajandar, Saumitra, Lim, Sin Leng, Dong, Yuan, D'Costa, Vijay Richard, Osipowicz, Thomas, Tok, Eng Soon, Yeo, Yee-Chia
• Format: Article
• Language: English
• Subjects: ABUNDANCE; ANNEALING; Applied physics; ATOMS; Bias; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CONCENTRATION RATIO; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Crystal structure; Crystallinity; Dark current; DOPED MATERIALS; Doping; Epitaxial growth; FABRICATION; GALLIUM; GERMANIUM; IMPLANTS; Lattice sites; LAYERS; MOLECULAR BEAM EPITAXY; MOLECULAR BEAMS; P-N JUNCTIONS; P-TYPE CONDUCTORS; PHOTODETECTORS; Photodiodes; PRECIPITATION; SEGREGATION; Silicon; SURFACES; TIN
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4947116

The in-situ Ga doping technique was used to form heavily p-type doped germanium-tin (Ge1− x Sn x ) layers by molecular beam epitaxy, avoiding issues such as Sn precipitation and surface segregation at high annealing temperatures that are associated with the alternative implant and anneal approach. In this way, an electrically active Ga concentration of up to ∼3.2 × 1020 cm−3 can be realized for Ge1− x Sn x . The impacts of varying the Ga concentration on the crystalline quality and the mobility of p-type Ge1−x Sn x were investigated. High crystalline quality Ge0.915Sn0.085 can be realized with an active Ga concentration of up to ∼1.2 × 1020 cm−3. More than 98% of the Sn atoms are located on substitutional lattice sites, although the substitutionality of Sn in p-type Ge1− x Sn x decreases with an increasing Ga concentration. When the Ga concentration introduced is higher than 3.2 × 1020 cm−3, excess Ga atoms cannot be substitutionally incorporated, and segregation of Ga and Sn towards the surface during growth is observed. The in-situ Ga-doped Ge0.915Sn0.085 epitaxy was integrated in a Ge0.915Sn0.085-on-Si p-i-n (PIN) photodiode fabrication process, and well-behaved Ge0.915Sn0.085/Si PIN junction characteristics were obtained. A large forward-bias current to reverse bias current ratio of 6 × 104 and a low reverse current (dark current) of 0.24 μA were achieved at Vbias  = −1 V.