dc.description.abstract | In this thesis, we demonstrated various types of High-Speed Avalanche photodiodes/Photodiodes (PDs) for Next generation ethernet system. One of them uni-traveling carrier photodiode (UTC-PD) with type-II GaAs0.5Sb0.5 (p)/In0.53Ga0.47As (i) hybrid absorber for further enhance the bandwidth-efficiency product of UTC-PD. In our proposed new UTC-PD structure, the p-type In0.53Ga0.47As absorption layer is replaced by the type-II GaAs0.5Sb0.5 (p)/In0.53Ga0.47As (i) hybrid absorber. Due to the narrowing of the bandgap and enhancement of the photo-absorption process at the type-II interface between the GaAs0.5Sb0.5 and In0.53Ga0.47As layers, our device shows an over 16.7 % improvement in the responsivity as compared to that of UTC-PD with the same thickness of pure In0.53Ga0.47As absorber (0.7 μm) and a zero optical coupling loss. Our demonstrated device with a simple top-illuminated structure offers a large active mesa (25 μm), a wide optical-to-electrical (O-E) bandwidth (33 GHz), a high responsivity (0.7 A/W), and a high saturation current (>5 mA) under 1.31 µm optical wavelength. Integration with a substrate lens for flip-chip bonding package and the application of Rx in DR-4 system. Such device can achieve a very-high responsivity (0.95 A/W), wide O-E bandwidth (33 GHz), high saturation current (4 mA), and high-sensitivity (-10 dBm OMA) without using any external lens in our package.Since this kind of receiver doesn’t have internal gain, therefore it requried strong optical local-oscillator (LO) power pumping to process the waek receive signal on the self heterodyne beating setup.In order to overcome the aforementioned isuse, a novel In0.52Al0.48As based top-illuminated avalanche photodiode (APD) is demonstrated. By combining the composite charge-layer design with a special p-side up etched mesa structure to zero the electric (E)-field at the periphery of this APD’s multiplication (M-) layer, the edge breakdown phenomenon can be eliminated. This in turn leads to the simultaneous high-speed, high-saturation-power, high responsivity, and low-dark current performance of our APDs characteristics, which are essential for high-performance coherent receiver applications. The demonstrated device with its simple top-illuminated structure exhibits a wide optical-to-electrical (O-E) bandwidth (21 GHz), high responsivity (5.5 A/W at 0.9 Vbr), and saturation current as high as 8 mA with a large active diameter of 24 μm for easy optical alignment. Furthermore, the nonlinear driving of a wavelength sweeping laser in the self-heterodyne beating setup can generate an optical pulse train like waveform, providing an effective optical modulation depth of up to 158%, which leads to a maximum photo-generated RF power (at 10 GHz) from our APD be as high as +5.5 dBm. Futhermore, in order to fulfill the bandwidth requirement for next generation ethernet systems, we require 100G APDs. We demonstrated a novel vertical-illuminated avalanche photodiode (APD) with a In0.52Al0.48As multiplication (M-) layer. The cascaded M-layer design combined with the unique p-side up mesa structure allows relaxation of the fundamental trade-off between the gain-bandwidth product and the dark current. This leads to the simultaneous high-responsivity, high-speed, high-saturation-power, and low-dark current characteristics of our APDs. At around 0.9 Vbr operation, the demonstrated device with its simple top-illuminated structure and large active window (mesa) diameter of 14 (24) μm exhibits a high responsivity (2.23 A/W), wide optical-to-electrical bandwidth (30 GHz), large gain-bandwidth product (270 GHz), low dark current (~200 nA), and a saturation current as high as 11 mA. In order to further improve Gain Bandwidth Product (GBP), flip-chip bonding APDs with 14μm window diameters are demonstrated having wide-bandwidth (36GHz), high-responsivity (3.4A/W), low dark current (175nA) and high MMW output power (-1dBm at 40GHz) can be achieved simultaneously with 12.5mA Isat under 0.9Vbr. The excellent performance of this APDs structure opens up new possibilities to further enhance the sensitivity performance of receivers for coherent communications or 106 Gbit/sec PAM-4 applications. | en_US |