The heterogeneous integration of III–V devices with Si-CMOS on a common Si platform has shown great promise in the new generations of electrical and optical systems for novel applications, such as HEMT or LED with integrated control circuitry. For heterogeneous integration, direct wafer bonding (DWB) techniques can overcome the materials and thermal mismatch issues by directly bonding dissimilar materials systems and device structures together. In addition, DWB can perform at wafer-level, which eases the requirements for integration alignment and increases the scalability for volume production. In this paper, a brief review of the different bonding technologies is discussed. After that, three main DWB techniques of single-, double- and multi-bonding are presented with the demonstrations of various heterogeneous integration applications. Meanwhile, the integration challenges, such as micro-defects, surface roughness and bonding yield are discussed in detail.

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We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.

A method for absolute evaluation of alloy composition and strain in AlGaN buffer layers in GaN/Si system is described, which can be applied to any III-nitride alloys hetero-epitaxially grown on Si (111) or sapphire (0001) substrate. Absolute measurements of reciprocal space maps of (10-14) nitride layers are performed with the help of Si (313) reciprocal lattice points. The alloy composition and strain-relaxation state in all layers are directly calculated from the absolute values of reciprocal lattice points referenced to the Si substrate. The proposed method of analysis using Si substrate is more accurate than currently favored method in which an epitaxial GaN layer is used as the reference. The knowledge of strain state and alloy composition with greater accuracy would be useful in designing and growing III-nitride devices.

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