Qiugui Zhou

High-Power V-Band InGaAs/InP Photodiodes

InGaAs/InP-modified uni-traveling carrier photodiodes with cliff layer were designed and fabricated for V-band (50-75 GHz) applications. The devices were flip-chip bonded on AlN submounts for efficient heat dissipation. A high-impedance transmission line was designed to compensate for the parasitic capacitance and enhance the bandwidth. Devices with 3-dB bandwidths of 50 and 65 GHz demonstrated high-output RF power of 20.3 and 15.9 dBm, respectively.

InP-based waveguide photodiodes heterogeneously integrated on silicon-on-insulator for photonic microwave generation

High-linearity modified uni-traveling carrier photodiodes on silicon-on-insulator with low AM-to-PM conversion factor are demonstrated. The devices deliver more than 2.5 dBm RF output power up to 40 GHz and have an output third order intercept point of 30 dBm at 20 GHz. Photodiode arrays exceed a saturation current-bandwidth-product of 630 mA · GHz and reach unsaturated RF output power levels of 10 dBm at 20 GHz.

High-Power and High-Linearity Photodetector Modules for Microwave Photonic Applications

We demonstrate hermetically packaged InGaAs/InP photodetector modules for high performance microwave photonic applications. The devices employ an advanced photodiode epitaxial layer known as the modified uni-traveling carrier photodiode (MUTC-PD) with superior performance in terms of output power and saturation. To further improve the thermal limitations, the MUTC-PDs were flip-chip bonded on high thermal conductivity substrates such as Aluminum Nitride (AlN) and Diamond. Modules using chips with active area diameters of 40, 28, and 20 μm were developed. The modules demonstrated a 3-dB bandwidth ranging from 17 GHz up to 30 GHz. In continuous wave mode of operation, very high RF output power was achieved with 25 dBm at 10 GHz, 22 dBm at 20 GHz, and 17 dBm at 30 GHz. In addition, the linearity of the modules was characterized by using the third order intercept point (OIP3) as a figure of merit. Very high values of OIP3 were obtained with 30 dBm at 10 GHz, 25 dBm at 20 GHz and more than 20 dBm at 30 GHz. Under short pulse illumination conditions and by selectively filtering the 10 GHz frequency component only, a saturated power of >21 dBm was also measured. A very low AM-to-PM conversion coefficient was measured, making the modules highly suitable for integration in photonic systems for ultralow phase noise RF signal generation.

High-power flip-chip mounted photodiode array

Four-element modified uni-traveling-carrier (MUTC) photodiode arrays (PDA) flip-chip bonded onto transmission lines on AlN substrates are demonstrated. High RF output powers of 26.2 dBm and 21.0 dBm are achieved at 35 GHz and 48 GHz, respectively, using a PDA with 28-μm diameter photodiodes. A systematic comparison between a PDA with four 20 μm-diameter elements and a discrete detector with the same active area (40-μm diameter) is presented. The PDA achieved higher output power and thermal dissipation compared to its discrete counterpart.

GaN/SiC avalanche photodiodes

Near ultraviolet-sensitive separate absorption and multiplication avalanche photodiodes with GaN/SiC epitaxial layers grown on SiC substrate were fabricated. Dark current < 1 pA at 90% breakdown voltage, maximum multiplication gain of ∼105, and responsivity exceeding 4.2 A/W at 365 nm were achieved.

Geiger-Mode Operation of Ge-on-Si Avalanche Photodiodes

Single-photon detection is reported for Ge-on-Si separate-absorption-charge-multiplication avalanche photodiodes. Single-photon detection efficiency of 14%, dark count rate of 108 s-1, and timing resolution of 117 ps were achieved.

Proton-Implantation-Isolated Separate Absorption Charge and Multiplication 4H-SiC Avalanche Photodiodes

We report reach-through structure 4H-SiC avalanche photodiodes isolated by proton implantation. These devices achieved low dark current (85 pA at a gain of 1000) and high external quantum efficiency ( 75% at 260 nm).

Laser-textured silicon photodiode with broadband spectral response

A femtosecond-laser-textured Si photodetector is reported. Broadband spectral optical response is detected from UV to NIR. A quantum efficiency of greater than 80% from 490  nm to 780  nm has been achieved. The quantum efficiency at 245  nm is 62%, which is comparable to UV-enhanced Si photodiodes. The bandwidth of a 250-μm-diameter device is 60  MHz.

SiC avalanche photodiode array with microlenses

A simple technique to incorporate microlenes with small photodiode arrays is demonstrated and analyzed. Using this method, the fill factor was increased from 2.6% to 22.4% for a two by two array. Simulation results are also shown. The photocurrent with microlens was approximately 8.6 times larger than without the microlens, which is consistent with simulation results.

Improved sinusoidal gating with balanced InGaAs/InP Single Photon Avalanche Diodes

We report balanced InGaAs/InP single photon avalanche diodes (SPADs) operated in sinusoidal gating mode with a tunable phase shifter to reduce common mode noise. This technique enables detection of small avalanche pulses, which results in reduced afterpulsing. For laser repletion rate of 20 MHz at 240 K, the dark count rate for photon detection efficiency of 10% is 8.9 kHz.