Investigations of low threading dislocation density (TDD) Ge growth using reduced pressure chemical vapor deposition for photonics application are reviewed. By interrupting the Ge growth process and annealing for several times during Ge epitaxy (cyclic annealing), TDD of below 1×106 cm-2 is achieved for 4.7 μn thick Ge. Root mean square of roughness below 0.5 nm is realized. Thin and low TDD Ge layer fabrication is demonstrated by depositing thick Ge with cyclic annealing process followed by HCl etching. Dislocation4 free area of local Ge on insulator is formed between  and [1-10] direction by lateral selective Ge growth in cavity between SiO2 cap and buried oxide, which is formed by sacrificial Si etching. Using an atomic-layer-doping approach, self-limitation of incorporated P dose at ∼1/4 monolayer is obtained offering heavy n-doping in Ge. P diffusion suppression by delta-doped Si in Ge is observed. By Ge growth followed by HCl etching process, photodiode with one order of magnitude lower dark current compared to standard Ge growth with cyclic annealing is fabricated.