); [EMAIL_ADDRESS] (T.A. ); [EMAIL_ADDRESS] (H.N. ); [EMAIL_ADDRESS] (T.K. ); [EMAIL_ADDRESS] (T.K. ); [EMAIL_ADDRESS] (T.T. ); [EMAIL_ADDRESS] (S.M.) [PERSON]  
1 NTT Device Technology Labs, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan; [EMAIL_ADDRESS] (T.H. ); [EMAIL_ADDRESS] (T.A. ); hidetaka.nishi.sftho.nt.co.jp (H.N. ); [EMAIL_ADDRESS] (T.A. ); [EMAIL_ADDRESS] (H.N. ); [EMAIL_ADDRESS] (T.K. ); [EMAIL_ADDRESS] (T.T. ); [EMAIL_ADDRESS] (S.M.) [PERSON]  
1 NTT Device Technology Labs, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan; [EMAIL_ADDRESS] (T.H. ); takuma. promising because mature complementary-metal-oxide-semiconductor (CMOS) fabrication technology enables the integration of various optical devices into a compact chip [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. A limitation of a Si-photonics-based PIC is the lack of a reliable, efficient and low-power-consumption light source due to its indirect bandgap. Accordingly, the integration of direct-bandgap III-V semiconductors on Si is desirable. In particular, indium phosphide (InP) and its related materials are widely used for developing high-performance optical transmitters such as directly modulated lasers (DMLs), electro-absorption modulator-integrated distributed feedback (EADFB) lasers and Mach-Zehnder modulators (MZMs) [11; 12; 13; 14; 15; 16; 17; 18]. Therefore, several hybrid integration techniques are used to develop III-V/Si hybrid PICs [4; 19; 20; 21; 22]. Among the hybrid integration techniques, direct epitaxial growth of III-V materials on a Si substrate has been attracting much attention for over 30 years because it is the most promising technique in terms of cost and scalability. However, there are fundamental difficulties that limit crystal quality such as differences in lattice constant, differences in the coefficient of thermal expansion (CTE), and the formation of anti-phase boundaries (APBs). In 1990, [PERSON] et al. demonstrated the room-temperature (RT) operation of indium-gallium-arsenide phosphide (InGaAsP) lasers directly grown on a Si substrate [23]. However, a buffer layer thicker than 15 \(\upmu\)m was required, making them difficult to optically connect to Si-photonics devices. Much effort has been made to improve the crystal quality of multi-quantum wells (MQWs) with thinner buffer layers [24; 25]. In addition, III-V quantum dot (QD) lasers directly grown on a Si substrate that exhibit >100 mW optical output power have been demonstrated [26; 27]. This can be achieved because QDs are insensitive to threading dislocations (TDs) compared with QWs. However, these \"blanket\" epitaxial growth techniques still require a thick buffer layer (typically >2 \(\upmu\)m). In contrast, direct selective epitaxy using defect filtering with selective-area growth masks enable the integration of high-quality III-V layers on a Si substrate without requiring a thick buffer layer [28; 29; 30; 31; 32]. Using the defect filtering method, various lasers with optical pumping have been demonstrated. On the other hand, electrically driven lasers that can emit output power required for data-center application have yet to be reported. This seems to correlate with the difficulty of growing ternary and quaternary compound materials, such as indium-gallium arsenide (InGaAs), InGaAsP, and indium-gallium-aluminum arsenide (InGaAlAs), because the crystal composition of these materials depends on both the mask structure and distance from the mask edge [33]. In addition, the structural limitation of the III-V device layer due to the selective-area growth masks makes it difficult to fabricate a _p-i-n_ junction, which is necessary for current injection. Direct- and adhesive-bonding techniques are another possible solution to achieve wafer-scale heterogeneous integration because bonding prevents the formation of TDs and APBs in III-V layers [34; 35].