We investigate the growth of InP-on-GaAs combined with the advantages of double low-temperature （LT） buffers and strained layer surperlattices （SLSs）. It is found that LT-InP/LT-GaAs double LT buffers are more effective for strain accommodation than a LT-InP single buffer in InP-on-GaAs. On the other hand, there is an optimal thickness for LT-GaAs for a given thickness of the LT-InP layer,at which the double LT buffers can reach the best state for strain ad- justment. Furthermore,the position of insertion of SLSs should be carefully designed because the distance above the InP/ buffer interface plays an important role in threading dislocation interactions for dislocation reduction. As a result, the density of threading dislocations in the InP epilayer is markedly reduced. X-ray diffraction measurements show that the full width at half maximum of the ω/2θ rocking curve for the 2μm-thick InP epilayer is less than 200.
A novel resonant cavity enhanced(RCE) photodetector with flat-top and steep-edge response is presented.The response is obtained by designing a gradient-thickness P area in the absorption cavity.Simulation results show that the maximum and minimum values of the quantum efficiency in bandpass are 85.242% and 87.564% respectively,the ripple is about 3.6%,and 0.5 dB,3 dB and 20 dB bandwidths are 0.3 nm,0.4 nm and 1.2 nm,respectively.The mesa area is 10 μm×10 μm and the frequency response bandwidth is 87 GHz.Compared with similar photodetectors,this photodetector has high quantum efficiency,narrow spectral response linewidth,good flat-top and steep-edge response and ideal high-speed characteristics.
