Resonant-cavity separate absorption, charge and multiplication avalanche photodiodes with high-speed and high gain-bandwidth product

Previously, it has been shown that resonant-cavity separate-absorption-and-multiplication (SAM) avalanche photodiodes (APD's) exhibit high-speed and high gain-bandwidth products. In this letter, we describe a resonant-cavity SAM APD with an additional charge layer that provides better control of the electric field profile. These devices have achieved bandwidths as high as 33 GHz in the low-gain regime and a record gain-bandwidth product of 290 GHz. We also describe the correlation between the gain-bandwidth product and the doping level in the charge layer. With width dependent ionization coefficients, the current versus voltage (I-V) and gain-bandwidth simulations agree well with the measured results and indicate that even higher gain-bandwidth should be achievable with an optimized SACM APD structure.