Plasma-Assisted MOCVD Growth of Non-Polar GaN and AlGaN on Si(111) Substrates Utilizing GaN-AlN Buffer Layer

We report the growth of non-polar GaN and AlGaN films on Si(111) substrates by plasma-assisted metal-organic chemical vapor deposition (PA-MOCVD). Low-temperature growth of GaN or AlN was used as a buffer layer to overcome the lattice mismatch and thermal expansion coefficient between GaN and Si(111) and GaN’s poor wetting on Si(111). As grown, the buffer layer is amorphous, and it crystalizes during annealing to the growth temperature and then serves as a template for the growth of GaN or AlGaN. We used scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) characterization to investigate the influence of the buffer layer on crystal structure, orientation, and the morphology of GaN. We found that the GaN buffer layer is superior to the AlN buffer layer. The thickness of the GaN buffer layer played a critical role in the crystal quality and plane orientation and in reducing the cracks during the growth of GaN/Si(111) layers. The optimum GaN buffer layer thickness is around 50 nm, and by using the optimized GaN buffer layer, we investigated the growth of AlGaN with varying Al compositions. The morphology of the AlGaN films is flat and homogenous, with less than 1 nm surface roughness, and has preferred orientation in a-axis.

Optical and structural properties of the GaAs heterostructures grown using AlGaAs superlattice buffer layer on compliant Si(100) substrates with the preformed porous-Si (por-Si) layer.

360 nm and 700 nm thick GaAs layers were grown by MO MOCVD growth technique directly on compliant Si (100) substrate and on supper-lattice (SL) AlGaAs buffer layer. The XRD study revealed better structural quality for the sample grown on SL / por-Si buffer. AFM study revealed a smoother sample surface with blocks of more regular rectangular shape and larger size as well. Photoluminescence spectra of the samples revealed an energy shift of PL maximum intensity for both samples. Sample grown on SL buffer also showed higher PL intensity corresponding to better crystalline perfection.

InP based high speed p-i-n photodetector monolithic integrated with MQW semiconductor optical amplifier

We demonstrate an InP based high speed p-i-n photodetector monolithic integrated with MQW semiconductor optical amplifier. A butt-joint scheme is adopted to connect the SOA and evanescent wave photodetector. The chip allows separate design for SOA and PD and needs only two MOCVD growth steps, which promises high yield and reduced manufacturing cost. The fabricated 5×20 μm2 PD shows a low dark current of 300 pA at -3V. The optical gain bandwidth of the SOA is 50nm, covering whole c-band. Gain ripple of SOA is 0.5dB, indicating that internal parasitic reflectivity is negligible. For integrated chip with 500μm SOA, the on-chip gain and total chip responsivity at 1545 nm can reach 12.8 dB and 7.8 A/W respectively. Insertion loss of the butt-joint interface is estimated to be 1.05 dB/interface. Small signal 3dB bandwidth at -5V of the integrated chip reaches 20GHz, showing no deterioration compared to discrete PD.