Top-Illuminated In0.52Al0.48As-Based Avalanche Photodiode with Dual Charge Layers for High-Speed and Low Dark Current Performances

A novel type of top-illuminated, etch-mesa In_0.52Al_0.48As-based avalanche photodiode (APD) with high-speed (>25 Gb/s), low dark current performance has been demonstrated. The 25G APD device is composed of n-side down design with the In_0.52Al_0.48As multiplication (M) layer buried at the bottom to avoid the issues of surface breakdown and complex guard ring structure. In addition, we demonstrate that the new structure with two charge layers and triple mesas can effectively confine the electric-field within the center of M-layer and minimize the edge breakdown around the periphery of mesa. In contrast to the costly flip-chip bonding package with backside illumination, our demonstrated device is based on a simple top-illuminated structure that includes a large active diameter of 30 μm for easy optical alignment, a reasonable punch-through responsivity (0.7 A/W at 1.31 μm wavelength), and a good 3-dB optical-to-electrical (O-E) bandwidth (22.5 GHz) under low gain operations (M_G = ∼3). Furthermore, it can sustain the 3-dB bandwidth of 15 GHz over a wide range of launched optical power (-17 to +4.6 dBm) under a moderate gain (M_G = ∼5) operation at 1.31 μm wavelength. High-sensitivity (-16 dBm) for error-free 28 Gb/s operation can also be achieved at 1.55 μm wavelength.