Photodetectors

High-power flip-chip mounted photodiode array

“…The PDA characteristic impedance, Z 0 , can be calculated by inserting the ϵ eff and the dimensions of the transmission line into the CPW design equations [6]. The PDA can be considered as a capacitively loaded transmission line with [1]: where L' cpw (Z 0 /V 0 for a lossless transmission line) and C' cpw are per unit length inductance and capacitance of the transmission line, and C pd is the photodiode junction capacitance. Utilizing C pd values extracted from S-parameter measurement of discrete detectors and a ϵ eff of 10 (calculated for a transmission line sandwiched between AlN and InP), the resulting C cpw was 220 pF/m.…”

“…Advancements in bandwidth, saturation-current, and power handling have been made in the past decade by transitioning to new materials and epitaxial structures. The development of the InP based uni-traveling-carrier (UTC) epitaxial structure has enabled high bandwidths by eliminating transport of slow moving holes across the depletion region [1]. Although the carrier transit distance for UTC diodes is typically greater than that of PIN diodes, the total carrier transit time is less since electron mobility is an order of magnitude greater than hole mobility.…”

“…However, the detector bandwidth, which is determined by a combination of resistance-capacitance (RC) time-constant and carrier transit time limitations, has a more complicated but typically inverse relationship to the physical dimensions. In practice, increased bandwidth is typically achieved by decreasing device dimensions, sacrificing RF output capabilities [1].…”