Design, Fabrication and Characterization of Hetero-PN-junction Devices for Photovoltaic and Photodetection Applications

The main objective of this dissertation's research was to develop single-photon detectors with high detection efficiencies for photodetection application, as well as solar cells with high conversion efficiencies and radiance resistance for photovoltaic space applications. Hetero-PN-junctions, which can provide unique material combinations, were utilized in order to accomplish these goals. One of research focuses is on the high efficient four-junction solar cells using AlAsSb, InP, InGaAsP and InGaAs materials for space applications. The temperature and radiation effect on these solar cells performance were discussed. The effect of cell structure on the radiation response was studied. We fabricated the 1.0 eV InGaAsP cell, which is critical for this four-junction solar cell. A heterojunction AlInAs/InP tunnel diode, which interconnects the cells, was designed, fabricated and tested with low zero-bias resistivity of 4.76×10-3 ? cm2 and high peak tunnel current of 147 A/cm2. Avalanche photodiodes (APDs) with the structure of a single-avalanche-stage were proposed to achieve high gain, high speed, and low noise operation for telecommunication applications. Simulation results show that it is possible to realize such a device with the InGaAs/InGaAlAs/InAlAs/InGaAsP/InGaAs materials system by combing the high doping with the heterojunction band discontinuity. Mesa-terminated N = 1 APDs were fabricated with the procedure developed using the equipment and facilities available at UMBC cleanroom. Multiplication gains were demonstrated at low bias voltages of ~ 7 V. The results show the dark current decreased a factor of 10 at a gain of 10 by changing the p-dopant from Zn to carbon. We believe that the high performance device can be obtained by carefully controlling the doping profile. Photon counting (PC) detection devices in the 1.0-1.6 µm wavelength range are important for LIDAR image, remote sensing, standoff chemical detection, and deep-space communications. Lacking of sufficient single photon detection efficiency (SPDE), one of the most important performance metrics, has been a primary issue for PC devices operating at the near infrared wavelength range. A method to improve single photon avalanche photodiodes (SPADs) performance was proposed by reducing the voltage difference between the punch-through and breakdown voltages of APDs. SPADs based on the proposed structure were fabricated. Results demonstrate the improvement in the leakage current and the I-V characteristics of APDs. Device's dark count probability (DCP) and SPDE were measured using our innovative gated current bias scheme under different operating conditions to obtain a maximum SPDE. We found that the SPDE can be enhanced with the proposed structure and a SPDE of ~ 25% was achieved