Optical amplifier based on germanium and optical integrated device including the same

An optical amplifier comprising:

• a first semiconductor layer doped with a first-type dopant at a first concentration;
• a second semiconductor layer on the first semiconductor layer and spaced apart from the first semiconductor layer, the second semiconductor layer doped with a second-type dopant having a polarity that is opposite to a polarity of the first-type dopant;
• a conductive layer on the second semiconductor layer;
• a third semiconductor layer on the first semiconductor layer and doped with the first-type dopant at a second concentration that is greater than the first concentration;
• and
• a fourth semiconductor layer between the first semiconductor layer and the second semiconductor layer, the fourth semiconductor layer comprising germanium and being configured to amplify light in response to an electrical signal being applied to the conductive layer and the second semiconductor layer.