Study of In1-xGaxAsyP1-y Contact Layers in In0.53Ga0.47As p-i-n Photodiodes

• Main Authors: Shih-Ming Chuang, 莊仕銘
• Other Authors: Wei-Chou Hsu
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/66720709798362012519

碩士 === 國立成功大學 === 電機工程學系專班 === 97 === In this thesis, some low series resistance p-i-n photodiodes have been successfully fabricated and investigated by metal organic chemical vapor deposition (MOCVD). At present In0.53Ga0.47As p-i-n photodiodes have been applied in the fiber-optical communication, especially in large dimension MPD (Monitor Photo-Detector). On the other hand, small aperture photo-detectors have made remarkable progress in high speed and bandwidth devices. In order to achieve a low RC constant detector and keep a simple fabrication process, we propose the p-i-n PD with suitable In1-xGaxAsyP1-y contact layer. Among the several available epitaxial techniques, MOCVD epitaxial technique has been widely studied for InP based compound semiconductor. A series of measurements, including double-crystal X-Ray diffraction (DCXRD), photoluminescence (PL), Hall measurement and electro- chemical capacitance-voltage (ECV) profile are used to check material quality. For In0.53Ga0.47As absorption layer, a very low background concentration 8.31×1013cm-3 and good electron mobility 1.3×104cm2/v-s are achieved. Furthermore, lattice mismatch of epi-layer is well controlled within ± 150ppm. First, a fundamental In0.53Ga0.47As p-i-n photodiode without contact layer is fabricated. The dark current decreases with decreasing incident light absorption aperture area. But the forward voltage increases with decreasing incident light absorption aperture diameter. On the other hand, there is large resistance at small aperture diameter of fundamental In0.53Ga0.47As p-i-n photodiode without contact layer. By decreasing the aperture diameter of the p-i-n photodiode, the capacitance is reduced apparently. But the device without contact layer can’t still satisfy high speed performance due to the large series contact resistance issue. The high doping concentration of the p-InP cap layer above 5×1018cm-3 is difficult to achieve. For 1310nm and 1550nm application of the fiber-optical communication, In0.53Ga0.47As ternary contact ring is added on cap p-InP layer. Although In0.53Ga0.47As contact layer has lower energy gap and higher p-type doping concentration than the In1-xGaxAsyP1-y quaternary material. But the incident wavelength below 1650nm will be absorbed by In0.53Ga0.47As contact layer, the In0.53Ga0.47As ternary contact ring process is necessary for high response application. However the contact ring process will add the device complication and process cost. In this thesis, we propose a series of transparent In1-xGaxAsyP1-y contact layer (λ<1.31um) to simplify the device process. In order to attain high doping concentration and low series resistance, a In1-xGaxAsyP1-y contact layer is inserted between the p-InP cap and metal. The small aperture In0.53Ga0.47As p-i-n photodiodes with In1-xGaxAsyP1-y contact layer are demonstrated with low series resistance and low junction capacitance. As the wavelength of latticed-matched In1-xGaxAsyP1-y material increases, the zinc doping concentration and diffusion speed are higher. The fast lateral diffusion of In1-xGaxAsyP1-y layer will result high large dark current due to the lateral leakage current. Low zinc diffusion concentration improves little dark current a little. Fast lateral zinc diffusion in In0.784Ga0.216As0.474P0.526 layer (PL~1.225um) layer causes large leakage current. In0.784Ga0.216As0.474P0.526 layer (PL~1.225um) contact ring process is still necessary for low dark current. Finally, a small aperture In0.53Ga0.47As p-i-n PD with an In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) contact layer have been fabricated and demonstrated to achieve low contact resistance and good responsivity without contact ring process. The In0.784Ga0.216As0.474P0.526 layer (energy gap=1.012eV, PL~1.225um) and In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) are studied for contact layers. The doping concentrations we can achieve are from 1×1019cm-3 to 3×1018cm-3. The dark current of In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) contact layer is significantly lower than In0.784Ga0.216As0.474P0.526 layer (energy gap=1.012eV, PL~1.225um). As compared with p-InP contact layer, the In0.8929Gax0.1071As0.2346P0.7654 (energy gap=1.18eV, PL wavelength=1050nm) layers also reduce the forward bias voltage and the series resistance of photo-detector. Experimentally, the capacitance also decreases with the smaller aperture size. The PD with In0.8929Gax0.1071As0.2346P0.7654 (Eg=1.18eV, PL ~1050nm) contact layer has been successfully demonstrated to achieve low contact resistance without contact ring process.