High concentration phosphorus doping in Ge for CMOS-integrated laser applications

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Germanium is a promising material for the laser that can be monolithically integrated on Si complementary metal-oxide-semiconductor platform and has emission wavelength of 1550 nm for optical interconnect. To obtain significant optical gain, it is necessary to achieve high n-type doping concentration level, while avoiding the damage to Ge crystalline quality. In this paper, we report an ex-situ phosphorus diffusion doping of Ge film, based on low-temperature phosphosilicate glass (PSG) pre-deposition process such as spin-on-glass and sub-atmospheric chemical vapor deposition (SACVD) methods. Closely related to optical gain properties of Ge for Ge-on-Si laser application, the photoluminescence characteristics of Ge epitaxial film after P diffusion doping were investigated. In particular, SACVD-processed PSG deposited directly on Ge film without any Si capping layer successfully led to high phosphorus doping concentration of ∼10<SUP>19</SUP> cm<SUP>−3</SUP> deep inside Ge and dramatically enhanced photoluminescence intensity by more than 10 times compared to intrinsic Ge film. By using the SACVD-PSG based P doping process, we developed an inverted-rib Ge waveguide structure for more effective optical gain. In the inverted-rib Ge structure, the mode will be positioned upward and stay relatively away from the Ge-Si interface where many dislocations are located and, as a result, we can expect less optical loss due to scattering and the overall higher mode gain. As a very promising preliminary result, from optical-pumping of the inverted-rib Ge, a threshold-like behavior starting at 18 kW/cm<SUP>2</SUP> and amplified spontaneous emission around 1570 nm were demonstrated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ex-situ P diffusion to Ge with phosphosilicate glass (PSG) source was investigated. </LI> <LI> Sub-atmospheric CVD (SACVD)-based PSG and spin-on-dielectric process were compared. </LI> <LI> Photoluminescence (PL) from Ge increased most, when SACVD but no Si capping used. </LI> <LI> A novel, inverted-rib Ge waveguide structure is proposed for a low-threshold laser. </LI> <LI> Light emission threshold at lower optical pumping than prior reports was observed. </LI> </UL> </P>