High-speed and high-photocurrent InP-based uni-traveling-carrier photodiode

• Main Author: Meng, Qianqian
• Other Authors: Wang Hong
• Format: Theses and Dissertations
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Semiconductors; DRNTU::Engineering::Electrical and electronic engineering::Microelectronics
• Online Access: http://hdl.handle.net/10356/72531
• Institution: Nanyang Technological University

With the rapid development of modern optical communication technology, photodiodes (PDs) with high performance have attracted intensive research interests for the application of CATV network, photonic analog-to-digital converter and optical links to phased array antenna and so on. To meet the requirements of high speed, high responsivity and high photocurrent (power) operation, various types of PDs have been investigated. Uni-traveling-carrier photodiode (UTC-PD) has attracted much attention since it was proposed in 1997. Compared to conventional PIN-PD, UTC-PD has a unique mode of operation where only faster electrons serve as the active carriers, which can reduce the space charge effect and lead to much higher current, and higher speed operations. In this thesis, a top-illuminated InGaAs/InP UTC-PD which is able to achieve high speed, high photocurrent and high responsivity simultaneously at 1.55 µm has been realized. In general, InP-based UTC-PD consists of a p-type narrow-bandgap InGaAs light absorption layer and an n-type wide-bandgap InP carrier collection layer. The abrupt energy barrier at InGaAs/InP absorption/collection interface results in the blocking of electron flow, causing a buildup of stored charge, degrade DC performance at high current densities. It also limits the high-speed, high-photocurrent performance. To overcome this problem, compositional graded InGaAsP layers were normally inserted between the InGaAs absorption and InP collection layers. However, the insertion of the InGaAsP layers often results in the difficulty in growth process as well as results in the complexity of device fabrication. In our UTC-PD structure, a novel dipole-doped structure, in combination with a setback layer were employed at the interface between InGaAs/InP absorption and collection layers to suppress the current blocking effect. The new structure eases epi-layer growth and device fabrication. The design of layer thickness and layer structure has been optimized to maximize the 3-dB bandwidth of UTC-PD with dipole-doped structure without compromising the responsivity. The UTC-PD has been fabricated and characterized with DC and RF performances at 1.55 µm wavelength. The devices show a low dark current of nA range with highest photocurrent of 160 mA and high responsivity of 0.6A/W. 3-dB bandwidth of over 40 GHz, which is due to the limitation of equipment, has been obtained. Clear eye opening at 30 Gbit/s (limitation of equipment) with output RF power of 13.2 dBm have also been realized. A semi-analytical approach has been developed to model the dipole-doped UTC-PD. A 3-dB bandwidth of 103 GHz is predicted for the top-illumination UTC-PD with diameter of 18 µm.