| The metal-semiconductor-metal (MSM) photodetectors are designed, fabricated and characterized. For (50 μm)2 and (100 μm)2 detection areas, the dark current are 1.4 nA, 6 nA and the output pulses' width equal 26 psec and 37 psec respectively. Using E-beam lithography, MSM photodetectors with nanometer finger width are fabricated. In this case, the responsivity increases to 0.74 A/W.; To integrate the MSM with microwave circuits, a novel coplanar waveguide (CPW) to microstrip transition is proposed. Simulation results show that the return loss of the CPW-microstrip transition is less than −25 dB up to 13 GHz on InP substrate. Experimentally, the return loss of two back to back conductor backed (CPWG)-microstrip transitions is less than −12 dB up to 14 GHz on InP and is less than −15 dB up to 25 GHz on Alumina substrate.; Two MSM photodetectors are monolithically integrated with a coplanar waveguide to form a surface excited balanced detector working at 1.55 μm. A 9–10 dB noise cancellation is achieved. Homodyne balanced detection is experimentally tested. Relative intensity noise (RIN) and signal are cancelled meanwhile the signal which appears in the intermodulation term increase by 7 dB compared to a single detector.; To reduce the dark current in MSM, the epilayer is etched between the metals on the surface of the CPWG. Hence, the propagation characteristics of the CPWG with surface etching are studied. Numerical results, based on mode matching technique, show that surface etching between the metal electrodes can change the characteristic impedance by up to 30% and thus it can be used as a new design parameter for coplanar waveguide transmission lines.; Finally, a new application for MSM is presented. Simulation results, based on the drift diffusion model, show that the I-V characteristic depends on the position of the spot such that it moves upward and downward as the spot moves along the gap. Also, with asymmetric illumination, the MSM can be considered as a current source in which the direction of the current depends on the position of the spot. |
