Fabrication and Characteristics of Si-Based Metal-Semiconductor-Metal Photodetectors

• Main Authors: Li-Hong Laih, 賴利弘
• Other Authors: Jyh-Wong Hong
• Format: Others
• Language: en_US
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/50396341267984401568

博士 === 國立中央大學 === 電機工程研究所 === 87 === The fabrication and characteristics of the Si-based planar metal-semiconductor-metal photodetectors (MSM-PD''s) had been investigated in this dissertation. These MSM-PD''s could be easily integrated into the Si optoelectronic integrated circuits (OEIC''s) for the 0.83 mm short-haul fiber communication systems. There are mainly four topics in this investigation. In the first topic, the lifetime of photo-excited carriers in semiconductor was studied with a femtosecond time-resolved reflectivity measurement. The lifetime of photo-excited carriers is closely related to the transient fall-time of high speed photodetector. In this study, the lifetime of hydrogenated n-type amorphous Si (n-a-Si:H) and porous Si (PS) were measured and discussed individually. Experimentally, it was found lifetime of photo-excited carriers in PS was about 300 fs, and that for n-a-Si:H was about 130 fs. The second topic concerned the traditional MSM-PD''s with top-electrodes on Si wafer for detecting the 0.83 mm light. To improve the device dark-current and response speed, the various amorphous films (e.g. a-SiGe:H, a-Si:H, and a-SiC:H) were employed to enhance Schottky barrier-height. Furthermore, the effects of growth temperature, film thickness, and annealing treatment for various amorphous films on the device characteristics were also been investigated. It was obvious the employed amorphous barrier layer could reduce the device dark-current and increase the response speed effectively. In the third topic, the bottom-electrode MSM-PD''s (BMSM-PD''s) were investigated. For these devices, the light was absorbed in the amorphous layer upon the electrodes, and the device could be fabricated on Corning 7059 glass or other insulator (e.g. SiO2 film) for detecting the light having wavelength from 500 to 900 nm. The BMSM-PD usually had a much higher responsivity than that of the one having top-electrodes, since the top-electrode would impede the incident light. To further increase the responsivity of BMSM-PD, the n-a-Si:H was used as the light-absorbing layer alternatively. Also, a novel MSM-PD with the bottom ridged Cr electrodes and an absorption layer of 600 nm intrinsic hydrogenated amorphous silicon-germanium (i-a-SiGe:H) was fabricated on Corning 7059 glass. The ridged electrode structure could not only increase the volume of absorption region but also cause a stronger lateral electric field in the absorption region and hence could increase the responsivity of the device effectively. Th forth topic was related to the U-grooved MSM-PD''s (UMSM-PD''s). The UMSM-PD''s having various trench depths of interdigitated electrodes and an intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer on c-Si to form a heterojunction have been fabricated successfully on p-type [100] Si wafer. The U-grooved structures on c-Si were achieved with a simple orientation-dependent etching (ODE) process. Experimentally, an UMSM-PD with a 70 nm i-a-Si:H overlayer, 1.45 mm-deep recessed electrodes, and 3 mm finger width and spacing, had a full width at half maximum (FWHM) of 50.6 ps and a fall-time of 132 ps for its temporal response under a bias of 15 V. The significant improvements of transient response for UMSM-PD, as compared to the conventional one, were attributed to the trench electrodes resulted in a stronger lateral electric field in the light absorption region of photodetector.