Yimin Kang

Frequency response and bandwidth enhancement in Ge/Si avalanche photodiodes with over 840GHz gain-bandwidth-product

In this work we report a separate-absorption-charge-multiplication Ge/Si avalanche photodiode with an enhanced gain-bandwidth-product of 845 GHz at a wavelength of 1310 nm. The corresponding gain value is 65 and the electrical bandwidth is 13 GHz at an optical input power of -30 dBm. The unconventional high gain-bandwidth-product is investigated using device physical simulation and optical pulse response measurement. The analysis of the electric field distribution, electron and hole concentration and drift velocities in the device shows that the enhanced gain-bandwidth-product at high bias voltages is due to a decrease of the transit time and avalanche build-up time limitation at high fields.

Epitaxially-grown Ge/Si avalanche photodiodes for 1.3µm light detection

We designed and fabricated Ge/Si avalanche photodiodes grown on silicon substrates. The mesa-type photodiodes exhibit a responsivity at 1310nm of 0.54A/W, a breakdown voltage thermal coefficient of 0.05%/°C, a 3dBbandwidth of 10GHz. The gain-bandwidth product was measured as 153GHz. The effective k value extracted from the excess noise factor was 0.1.

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.

High performance Ge/Si avalanche photodiodes development in intel

Ge/Si avalanche photodiodes with record high gain-bandwidth and sensitivity for communication wavelength and high data rate, 10Gbps and 40Gbps, is demonstrated. These devices can be monolithically integrated with other silicon photonics components using CMOS technology.

A self-assembled microbonded germanium/silicon heterojunction photodiode for 25 Gb/s high-speed optical interconnects

A novel technique using surface tension to locally bond germanium (Ge) on silicon (Si) is presented for fabricating high performance Ge/Si photodiodes. Surface tension is a cohesive force among liquid molecules that tends to bring contiguous objects in contact to maintain a minimum surface energy. We take advantage of this phenomenon to fabricate a heterojunction optoelectronic device where the lattice constants of joined semiconductors are different. A high-speed Ge/Si heterojunction waveguide photodiode is presented by microbonding a beam-shaped Ge, first grown by rapid-melt-growth (RMG) method, on top of a Si waveguide via surface tension. Excellent device performances such as an operating bandwidth of 17 GHz and a responsivity of 0.66 and 0.70 A/W at the reverse bias of −4 and −6 V, respectively, are demonstrated. This technique can be simply implemented via modern complementary metal-oxide-semiconductor (CMOS) fabrication technologies for integrating Ge on Si devices.

Monolithic Ge/Si avalanche photodiodes

We demonstrate mesa-type and waveguide-type Ge/Si avalanche photodiodes both with high performances. The gain-bandwidth product was measured as high as 340GHz and the receiver sensitivity was −28dBm and −30.4dBm for mesa-and waveguide-type devices, respectively.

Resonant normal-incidence separate-absorption-charge-multiplication Ge/Si avalanche photodiodes.

In this work the impedance of separate-absorption-charge-multiplication Ge/Si avalanche photodiodes (APD) is characterized over a large range of bias voltage. An equivalent circuit with an inductive element is presented for modeling the Ge/Si APD. All the parameters for the elements included in the equivalent circuit are extracted by fitting the measured S(22) with the genetic algorithm optimization. Due to a resonance in the avalanche region, the frequency response of the APD has a peak enhancement when the bias voltage is relatively high, which is observed in the measurement and agrees with the theoretical calculation shown in this paper.

Derivation of the Small Signal Response and Equivalent Circuit Model for a Separate Absorption and Multiplication Layer Avalanche Photodetector

A small signal analysis for a separate-absorption-charge-multiplication (SACM) avalanche photodetector (APD) is presented for the general case when the electrons and the holes have different ionization coefficients and different velocities. The analytic expressions for the impedance and frequency response are given and a simplified equivalent circuit (including an inductance with a series resistance in parallel with a capacitance) for the APD is obtained. The calculation and experimental results show that the impedance of the APD operated at high bias voltages has a maximal value at a certain frequency due to the resonance of the LC-circuit, and this is the origin for a peak-enhancement of the frequency response.

Avalanche photodiode punch-through gain determination through excess noise analysis

A new approach to determine the multiplication gain at punch-through for an avalanche photodiode with separate absorption and multiplication regions from excess noise measurement is discussed. Correctly determining the gain at punch-through is crucial for characterizing performance parameters of this type of avalanche photodiode. In order to illustrate the viability of this technique, in this work, a Ge on Si avalanche photodiode is analyzed. At a punch-through bias of 15 V, the multiplication gain was determined to be ∼1.54 while a simulation based on the device structure yielded a punch-through gain of 1.65.

Self-Aligned Microbonded Germanium Metal–Semiconductor–Metal Photodetectors Butt-Coupled to Si Waveguides

We present a butt-coupled Germanium (Ge) metal-semiconductor-metal photodetectors on silicon (Si) waveguides. This device is implemented by a novel process using self-aligned microbonding technique and rapid-melt-growth method for monolithically integrating single-crystal Ge and Si devices on the same plane. Through inserting a thin amorphous Si (a-Si) layer between the Ge and metal contact, the Schottky barrier height is modulated, which effectively reduces the dark current and increases the operation speed. The fabricated device shows a low dark current of 0.24 μA, a 3 dB bandwidth of 15 GHz and a responsivity of 0.25 A/W, at a bias voltage of -2.6 V for wavelength 1310 nm.