Ultra-fast, High Saturation Current, InGaAs/InP Photodetectors

In Phase II, we propose to develop high saturation current photodiodes that will meet the following design criteria: (a) Responsivity > 0.65 A/W, (b) 1 dB compression current > 100 mA, (c) Bandwidth DC to 18 GHz,(d) Wavelength response of 1300 to 1550 nm, and (e) OIP3 of +50 dBm. Three different photodiode designs will be tested for maximum saturation current: Partially Depleted Absorber (PDA), Dual-depletion Region (DDR), and Charge Compensated Uni Traveling Carrier (CC UTC). A comparative study of these three designs will determine which structure is more suitable for the above design goals. As saturation current levels increase above 100 mA, the problem of excessive Joule heating (multiple of voltage bias and photodiode current) creates the problem of "thermal runaway" leading to eventual device failure. We will investigate "wafer bonding" of InGaAs photodiodes to silicon wafers for better heat removal caused by Joule heating. This will ultimately lead to a more reliable photodiode. Additionally, both single and doublet Graded Index (GRIN) lenses will be used for optical beam shaping to convert a Gaussian beam to a flattop beam. This will help us achieve the above listed five goals.