Characteristics and analysis of high speed InGaAs/InP uni-traveling-carrier photodiodes (UTC-PD)

With the development of broadband and high-frequency photonic systems, the photodiode with both high output power and high speed operating characteristics becomes attracti ve. The novel uni-traveling-carrier photodiode (UTC-PD) can realize these characteristics simultaneously. Compared with conventional photodiodes, this superior device improves the device performance in photonic system owing to its unique structure whose active region comprises a neutral or p-type narrow-gap light absorption layer and an undoped or slightly n-type wide-gap carrier collection layer. By adopting thi s structure, the photoresponse of UTC-PD is solely contributed by electrons whose transmit velocity is an order of magnitude faster than that of holes. As a consequence, the device demonstrates high performance of higher-speed operation as well as high-output saturation current. However, although UTC-PDs already show superior features, most of the InP-based UTC-PDs still need InGaAsP compositional graded quaternary structures at InGaAs and InP interface to smoothen the bandgap discontinuity. Consequently, the fabrication process and growth of materials will become more difficult and complicated. In order to resolve this limitation of intrinsic tradeoff between device's performance and growth as well as process complexity, a UTC-PD with dipoledoped interface layer is proposed in this work. Furthermore, a thicker collection layer of 350 nm is employed to obtain better performance. By measuring this photodiode with its dark current, series resistance, bandwidth and photocurrent, we can conclude that it shows excellent performances. To be specific, the device can reach a high 3-dB bandwidth of 570Hz under a constant optical power of 100 m Wand a reverse bias voltage of 6V.Master of Science (Electronics