Butt-joint regrowth method by MOCVD for integration of evanescent wave coupled photodetector and multi-quantum well semiconductor optical amplifier

We have realized integration of evanescent wave coupled photodetector(ECPD)and multi-quantum well(MQW)semiconductor optical amplifier(SOA)on MOCVD platform by investigating butt-joint regrowth method of thick InP/InGaAsP waveguides to deep etched SOA mesas.The combination of inductively coupled plasma etching and wet chemical etching technique has been studied to define the final mesa shape before regrowth.By comparing the etching profiles of different non-selective etchants,we have obtained a controllable non-reentrant mesa shape with smooth sidewall by applying one step 2 HBr:2 H_(3)PO_(4):K_(2)Cr_(2)O_(7)wet etching.A high growth temperature of 680℃is found helpful to enhance planar regrowth.By comparing the growth morphologies and simulating optical transmission along different directions,we determined that waveguides should travel across the regrowth interface along the[110]direction.The relation between growth rate and mask design has been extensively studied and the result can provide an important guidance for future mask design and vertical alignment between the active and passive cores.ECPD-SOA integrated device has been successfully achieved by this method without further regrowth steps and provided a responsivity of 7.8 A/W.The butt-joint interface insertion loss is estimated to be 1.05 dB/interface.

Plasma Triggered Grain Coalescence for Self-Assembly of 3D Nanostructures

Grain coalescence has been applied in many areas of nanofabrication technology, including modification of thinfilm properties, nanowelding, and self-assembly of nanostructures. However, very few systematic studies of selfassembly using the grain coalescence, especially for threedimensional(3D) nanostructures, exist at present. Here, we investigate the mechanism of plasma triggered grain coalescence to achieve the precise control of nanoscale phase and morphology of the grain coalescence induced by exothermic energy. Exothermic energy is generated through etching a silicon substrate via application of plasma. By tuning the plasma power and the flow rates of reactive gases, different etching rates and profiles can be achieved, resulting in various morphologies of grain coalescence. Balancing the isotropic/anisotropic substrate etching profile and the etching rate makes it possible to simultaneously release 2D nanostructures from the substrate and induce enough surface tension force,generated by grain coalescence, to form 3D nanostructures.Diverse morphologies of 3D nanostructures have been obtained by the grain coalescence, and a strategy to achieve self-assembly, resulting in desired 3D nanostructures, has been proposed and demonstrated.