Yaojia Chen

Low-noise AlInAsSb avalanche photodiode

We report low-noise avalanche gain from photodiodes composed of a previously uncharacterized alloy, Al0.7In0.3As0.3Sb0.7, grown on GaSb. The bandgap energy and thus the cutoff wavelength are similar to silicon; however, since the bandgap of Al0.7In0.3As0.3Sb0.7 is direct, its absorption depth is 5 to 10 times shorter than indirect-bandgap silicon, potentially enabling significantly higher operating bandwidths. In addition, unlike other III-V avalanche photodiodes that operate in the visible or near infrared, the excess noise factor is comparable to or below that of silicon, with a k-value of approximately 0.015. Furthermore, the wide array of absorber regions compatible with GaSb substrates enable cutoff wavelengths ranging from 1u2009μm to 12u2009μm.

AlInAsSb separate absorption, charge, and multiplication avalanche photodiodes

We report Al<inf>x</inf>In<inf>1−x</inf>Asj, Sb<inf>1−y</inf>-based separate absorption, charge, and multiplication avalanche photodiodes (APDs) that operate in the short-wavelength infrared spectrum. These APDs exhibit low excess noise factor, corresponding to k = 0.01, and low dark current.

AlInAsSb/GaSb staircase avalanche photodiode

Over 30 years ago, Capasso and co-workers [IEEE Trans. Electron Devices 30, 381 (1982)] proposed the staircase avalanche photodetector (APD) as a solid-state analog of the photomultiplier tube. In this structure, electron multiplication occurs deterministically at steps in the conduction band profile, which function as the dynodes of a photomultiplier tube, leading to low excess multiplication noise. Unlike traditional APDs, the origin of staircase gain is band engineering rather than large applied electric fields. Unfortunately, the materials available at the time, principally AlxGa1−xAs/GaAs, did not offer sufficiently large conduction band offsets and energy separations between the direct and indirect valleys to realize the full potential of the staircase gain mechanism. Here, we report a true staircase APD operation using alloys of a rather underexplored material, AlxIn1−xAsySb1−y, lattice-matched to GaSb. Single step “staircase” devices exhibited a constant gain of ∼2×, over a broad range of applied ...

High-Power and High-Speed Heterogeneously Integrated Waveguide-Coupled Photodiodes on Silicon-on-Insulator

InP-based high-power and high-speed modified unitraveling carrier photodiodes heterogeneously integrated on silicon-on-insulator waveguides are demonstrated. Internal responsivity up to 0.95A/W and bandwidth up to 48 GHz have been achieved. The maximum RF output power of a 20×35 μm2 photodiode was 16.6, 15.8, and 13.5 dBm at 10, 20, and 30 GHz, respectively. The maximum output RF power of a 10×μm2 photodiode was 12 dBm at 40 GHz. Using the same integration technology, we show that balanced waveguide photodiodes reach 0.78-A/W internal responsivity, 14-GHz bandwidth, and >20-dB common-mode rejection ratio. In the differential mode, the unsaturated RF output power was 17.2 dBm at 10 GHz and 15.2 dBm at 20 GHz.

High quantum efficiency GaP avalanche photodiodes

Gallium Phosphide (GaP) reach-through avalanche photodiodes (APDs) are reported. The APDs exhibited dark current less than a pico-ampere at unity gain. A quantum efficiency of 70% was achieved with a recessed window structure; this is almost two times higher than previous work.

Solar-blind AlxGa1−xN/AlN/SiC photodiodes with a polarization-induced electron filter

Heterogeneous n-III-nitride/i-p silicon carbide (SiC) photodetectors have been demonstrated that enable the tailoring of the spectral response in the solar blind region below 280u2009nm. The negative polarization induced charge at the aluminum gallium nitride (AlxGa1−xN)/aluminum nitride (AlN) interface in conjunction with the positive polarization charge at the AlN/SiC interface creates a large barrier to carrier transport across the interface that results in the selective collection of electrons photoexcited to the Γ and L valleys of SiC while blocking the transport of electrons generated in the M valley. In addition, the AlxGa1−xN alloys act as transparent windows that enhance the collection of carriers generated by high energy photons in the fully depleted SiC absorption regions. These two factors combine to create a peak external quantum efficiency of 76% at 242u2009nm, along with a strong suppression of the long-wavelength response from 260u2009nm to 380u2009nm.Heterogeneous n-III-nitride/i-p silicon carbide (SiC) photodetectors have been demonstrated that enable the tailoring of the spectral response in the solar blind region below 280u2009nm. The negative polarization induced charge at the aluminum gallium nitride (AlxGa1−xN)/aluminum nitride (AlN) interface in conjunction with the positive polarization charge at the AlN/SiC interface creates a large barrier to carrier transport across the interface that results in the selective collection of electrons photoexcited to the Γ and L valleys of SiC while blocking the transport of electrons generated in the M valley. In addition, the AlxGa1−xN alloys act as transparent windows that enhance the collection of carriers generated by high energy photons in the fully depleted SiC absorption regions. These two factors combine to create a peak external quantum efficiency of 76% at 242u2009nm, along with a strong suppression of the long-wavelength response from 260u2009nm to 380u2009nm.

Deep ultraviolet enhanced silicon carbide avalanche photodiodes

High sensitivity deep ultraviolet (DUV) photodetectors operating at wavelengths shorter than 280 nm are useful for various applications, including chemical and biological identification, optical wireless communications, and UV sensing systems (1). While semiconductor avalanche photodiodes (APDs) can be more compact, lower cost and more rugged than the commonly used photomultiplier tubes (PMTs), commercially available devices such as silicon (Si) single photon counting APDs have poor DUV single photon detection efficiency. In contrast, silicon carbide (SiC) APDs are ideal for high-sensitivity detection applications, as they can possess very low dark currents, small k factor, and high gain (2). However, the responsivity of these devices diminishes at wavelengths shorter than 260 nm due to increasing absorption and carrier generation in the top doped layer of this device, the short diffusion length of minority carriers in this region, and the presence of a high density of surface states.

Low-noise high-gain tunneling staircase photodetector

Avalanche photodiodes (APD) are important components in short-wave and mid-wave infrared detection systems (imaging, laser radar, communications, etc.) because their internal gain can improve receiver sensitivity and enable the detection of weak photon fluxes. However, gain originates from impact ionization, a stochastic process that results in excess noise and limits the gain-bandwidth product. The staircase APD was proposed as the solid-state analog of the photomultiplier tube where impact ionization events occur proximate to the sharp bandgap discontinuity of each step. As a result, the gain process is more deterministic, with concomitant reduction in gain fluctuations and, thus, lower excess noise. An additional advantage of the staircase structure is that the kinetic energy change required to initiate impact ionization events is supplied by band engineering and a modest applied field, rather than large bias, which is typically 10s of Volts for conventional APDs. Unfortunately, initial studies of staircase APDs used the AlxGai_xAs material system, which has inadequate band offsets and the projected noise characteristics were never achieved, We recently demonstrated the first staircase APDs, where a single step exhibits a constant gain of ~2x over a range of bias, temperature, and excitation wavelength, enabled by the digital alloy growth of high-quality AlInAsSb, lattice-matched to GaSb across the full range of direct bandgap compositions.

Enhancing the deep ultraviolet response of 4H-silicon carbide-based photodiodes between 210 nm and 255 nm

This work demonstrates two novel 4H-SiC-based photodiode structures that enhance the response from ~200 nm to 260 nm by increasing the absorption of DUV photons within the high-electric-field depletion region and more efficiently collecting photo-generated carriers through drift as opposed to diffusion, despite the presence of surface recombination. In particular, the two devices discussed in this work have replaced the heavily doped, top-illuminated, n+-layer of conventional p-n--n+ diodes by a semi-transparent metal contact to create a p-n--metal based device and by an n-type, wider bandgap AlGaN layer to create a heterojunction 4H-SiC/AlGaN p-n--n+ based device.